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An analysis and simulation of solar water desalination systems

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An analysis and simulation of solar water desalination systems
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Ghadhban, Ahmed ( author )
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This dissertation presents theoretical analysis and simulations used to improve the performance of desalination systems and compares several solar desalination processes. This research demonstrates how to use modular approaches for the dynamic simulation and steady state analysis of desalination by using MATLAB r2016a Simulink. Data from NIST (National Institute of Standard and Technology) and from SAM Advisor (System Advisor Model) were used in this study. Three types of distilled water (pipe water, heavy water, and seawater) were used to compare the distilled fresh water produced from each solar desalination system. The potable water production rate from heating the feed water was calculated using empirical and theoretical modeling. Results of the modeling and experimental results were compared for both processes. The simulations, modeling, and optimization of desalination processes using computer design technology are discussed. The results from this research could be used to predict the operating conditions of desalination systems
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Thesis (M.S.)--University of Colorado Denver.
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Includes bibliographical references.
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by Ahmed Ghadhban.

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Full Text
AN ANALYSIS AND SIMULATION OF SOLAR WATER DESALINATION SYSTEMS
by
AHMED GHADHBAN B.S., University of Basrah, 2005
A thesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Master of Science Mechanical Engineering Program
2017


This thesis for the Master of Science degree by Ahmed Salim Hial Ghadhban has been approved for the Mechanical Engineering Program by
Peter Jenkins, Chair Kannan Permnath Maryam Derbeheshti
Date: May 13, 2017
11


Ghadhban, Ahmed (M.S., Mechanical Engineering Program)
An Analysis and Simulation of Solar Water Desalination Systems Thesis directed by Professor Peter Jenkins
ABSTRACT
This dissertation presents theoretical analysis and simulations used to improve the performance of desalination systems and compares several solar desalination processes. This research demonstrates how to use modular approaches for the dynamic simulation and steady state analysis of desalination by using MATLAB r2016a Simulink. Data from NIST (National Institute of Standard and Technology) and from SAM Advisor (System Advisor Model) were used in this study. Three types of distilled water (pipe water, heavy water, and seawater) were used to compare the distilled fresh water produced from each solar desalination system. The potable water production rate from heating the feed water was calculated using empirical and theoretical modeling. Results of the modeling and experimental results were compared for both processes. The simulations, modeling, and optimization of desalination processes using computer design technology are discussed. The results from this research could be used to predict the operating conditions of desalination systems.
The form and content of this abstract are approved. I recommend its publication.
Approved: Peter Jenkins
m


ACKNOWLEDGMENTS
I would like to thank my advisor, Professor Jenkins, for giving me the chance to work on this project. I am thankful for his help and patience. I also would like to thank my committee members: Dr. Premnath and Dr. Darbeheshti. Each one of them has provided me with opportunities to advance my study and provided encouragement along the way. Also, I appreciate the people who have supported me, especially my family, my parents, my wife and my friends. Moreover, I would like to thank the Department of Mechanical Engineering for allowing me to utilize the library and labs to complete my research. I greatly appreciate the Mechanical Department workshop for the construction of the PV Solar desalination system. Finally, I am grateful to everyone who has encouraged me to pursue my project.
IV


TABLE OF CONTENTS
CHAPTER
I INTRODUCTION.................................................1
1.1 Background..............................................1
1.2 Water Crises.............................................1
1.3 Research Motivation......................................2
1.4 Research Obj ectives.....................................2
1.4.1 Neural Networks for Modeling..........................3
1.4.2 Steady State and Dynamic Simulations..................3
1.4.3 Comparing Results.....................................3
1.5 Research Methods.........................................4
II PROPERTIES OF WATER.........................................5
2.1 ProducedW ater...........................................5
2.2 FeedWater................................................6
2.2.1 Brackish Water........................................6
2.2.2 Seawater..............................................7
III DESALINATION..............................................10
3.1 Desalination Use........................................10
3.2 Desalination Background.................................12
3.3 Desalination Process Classifications....................13
v


3.3.1 Membrane Process...........................................13
3.3.2 Thermal Process...........................................14
IV SOLAR ENERGY.....................................................20
4.1 Introduction of Solar Energy..................................20
4.2 Sun-Earth relationships.......................................20
4.3 Solar Radiation Definition....................................21
4.4 Solar Energy applications.....................................22
4.4.1 Suns energy capture ways..................................24
V PROJECT DESCRIBTION AND ANALYSIS.................................27
5.1 PV Solar Powered Desalination.................................27
5.1.1 System Outline.............................................28
5.1.2 Develop PV Solar Array and Batteries......................31
5.1.3 Size Heating Source.......................................38
5.1.4 Provide Heat to the Water.................................41
5.1.5 Condensing the Vapor......................................50
5.2 Solar Still...................................................53
5.2.1 Solar Still Elements.......................................53
5.2.2 Energy Balance............................................54
5.2.2.1 External Heat Transfer............................55
5.2.2.2 Internal Heat Transfer............................59
vi


VI RESULT
63
6.1 PV Solar Powered Desalination Results....................63
6.2 Solar Still Results......................................78
6.3 Comparing the results....................................81
VII DISCUSSION AND CONCLUSION..................................84
7.1 Discussion...............................................84
7.2 Conclusion...............................................85
7.3 Future Direction.........................................85
REFERENCES............................................................86
vii


LIST OF TABLES
TABLE
1. Drinkable water standard of water.........................................5
2. Water saline category.....................................................7
3. Major ion concentration in seawater.......................................9
4. PV solar electrical characteristics.......................................36
5. Thermophysical properties of air..........................................41
6. Feed water types yield....................................................76
viii


LIST OF FIGURES
FIGURE
2.1. Ions concentration in seawater.................................................8
3.1. Chart shows a fraction of the worldwide capacity of the desalination plants by regions. ................................................................................11
3.2. Installed desalination plants capacity in the USA and worldwide from 1950 to 200612
3.3. Thermal desalination process diagram..........................................14
3.4. Schematic diagram of multi-stage flash........................................15
3.5. Schematic diagram of multiple-effect distillation.............................16
3.6. Schematic diagram of vapor compression distillation...........................17
3.7. Global distribution of installed water desalination capacity by the technolog.18
4.1. Sun-Earth relationships.......................................................21
4.2. Variation of the solar radiation with the year................................22
4.3. Available solar energy in the United States...................................24
4.4. Photovoltaic cell panel.......................................................26
5.1. PV solar desalination system..................................................27
5.2. PV solar powered desalination schematic.......................................30
5.3. PV Module and batteries modeling in MATLAB/ Simulink..........................31
5.4. Ideal PV circuit..............................................................32
5.5. Equivalent circuit for PV module..............................................33
5.6. Typical P_V and I_V curve for PV module.......................................36
5.7. Heating source sizing in MATLAB/Simulink......................................39
5.8. Schematic of water evaporative in MATLAB/Simulink.............................45
IX


5.9. Two-Phase fluid properties block.................................................45
5.10. Water properties data (picture is taken from MATLAB)............................46
5.11. Rigid pipe block................................................................46
5.12. Heat balance for condensate.....................................................51
5.13. Schematic of water condensate in MATLAB/Simulink................................52
5.14. Solar still basin...............................................................54
5.15. Overall energy balance..........................................................55
5.16. Schematic of solar still desalination...........................................62
6.1. P-V curve characteristic..........................................................63
6.2.1-V curve characteristic...........................................................64
6.3. PV Array characteristics for P-V and I-V curves..................................65
6.4. Photovoltaic panel characteristics for different irradiance values (1000, 500, and 100)66
6.5. Actual power output in June in Denver for one PV panel............................67
6.6. Actual power output in June in Denver for three PV Panels.........................67
6.7. Water distilled flow rate for piped water.........................................68
6.8. Vapor-Water distilled temperature for piped water.................................69
6.9. Piped Water vapor fraction........................................................70
6.10. Piped Water distilled production in one hour...................................70
6.11. Piped Water distilled curve.....................................................71
6.12. Heavy Water distilled flow rate................................................71
6.13. Vapor and water distilled temperature for heavy water..........................72
6.14. Heavy Water production in one hour.............................................72
6.15. Heavy Water distilled curve.....................................................73
x


6.16. Heavy Water vapor fraction..................................................73
6.17. Seawater distilled flow rate.................................................74
6.18. Seawater distilled production in one hour...................................75
6.19. Comparing modeling results of water distilled from three water types........76
6.20. Distilled Seawater production done experimentally in one hour...............77
6.21. Comparing freshwater productivity for Seawater from experiment and modeling of PV
solar method..................................................................78
6.22. Solar Still modeling yield...................................................79
6.23. Water temperature and glass temperature......................................80
6.24. Reference experimental Solar Still distilled water..........................81
6.25. Comparing the freshwater results from the PV Solar modeling approach with the
freshwater from Solar Stills modeling for Seawater...........................82
6.26. Comparing the freshwater results from the PV Solar experimental approach with the
freshwater from Solar Stills experimental for Seawater.......................83
xi


CHAPTER I
INTRODUCTION
1.1 Background
The growing world population is rapidly increasing the demand for fresh water. Only about 2.5% of water that exists on earth is fresh water [27], and this water is not distributed equally. Groundwater constitutes 30% of the fresh water resources [4], but in arid and semi-arid areas, underground water is difficult to obtain and expensive to ship. Therefore, its necessary to develop alternatives to produce potable water from salt water. Fresh water is required for industrial, agricultural, and domestic uses. Clean water shortages are a major factor in economic development. The oceans provide 96.5% of earths water [27], but the salt concentration renders this water not suitable for human use. Salt concentration in oceans ranges from 33-37 ppt [7], Seawater desalination is considered the best option to meet the demands of fresh water globally. Desalination has already been successfully implemented in several countries: Europe, southern and western parts of the US, and North Africa.
1.2 Water Crises
Many countries lack natural sources of drinkable water, and consequently, 1 billion humans cannot access clean water [35], The potable water shortage has the worlds attention because water is necessary for the economic development and health to maintain the ecosystems [12], Continued efforts are made to develop methods to get fresh water from different sources to provide water to people, farmers, and factories. However, fresh water sources are limited, and retaining a balance in social and economic development results in an imbalance between water supply and demand, putting pressure on many countries water resources. The situation is further complicated because of the increasing rate of water
1


consumption, due to population growth and the social and economic development. Therefore, its crucial to increase the global availability of water sources.
In response to this water crisis, the desalination of seawater has become a main resource of water for the long-term, and has already been implemented in several countries. Among desalination processes, solar desalination is much more practical than other processes, especially in arid areas where many water resources are available but suffer from a lack of a power supply. In spite of its high cost, solar desalination has an advantage that satisfies a variety of demands, and it is a clean source of energy.
Because of the potential to produce fresh water and support life on earth, developing desalination processes is very important. Solar desalination, in particular, requires immediate and significant efforts to design improvements and controls for establishing the costs associated with producing this technology.
1.3 Research Motivation
The importance of desalinated water will only increase as the natural water sources are depleted. In order to solve the fresh water problem, new water resources should be discovered, and new techniques developed.
Desalination is considered a satisfactory technique for purifying conventional water sources. In several countries, fossil fuel has been used to provide power to water desalination systems. For small systems, low-cost, solar-powered water desalination may be preferred.
1.4 Research Objectives
The following topics will be analyzed in this research project:
a. Neural networks for the predictive modeling of water desalination.
b. Dynamic and steady-state simulations of a flash desalination system.
2


c. Comparison of the results between different types of solar desalination processes.
1.4.1 Neural Networks for Modeling
Applying artificial intelligence to the design and operation of desalination systems will lead to better designs and enhanced operation of these systems. This process is a good choice for neutral networks because of the complexity of the process.
The behavior is nonlinear with some degrees of freedom, and this nonlinearity is due to the physical properties of streams depending on the pressure, temperature, and salinity.
The amount of mass flow and heat transfer also contribute to the nonlinear behavior of the models in the thermal process. The neural network provides a suitable prediction model for the desalination modeling.
1.4.2 Steady State and Dynamic Simulations
The goals of simulation and modeling for the industrial processes are improved and optimized in this project. Steady state models are developed that involve algebraic equations.
The dynamic models are primarily applicable to estimate the performance and optimization of the system. The dynamic models involve differential and algebraic equations, which describe the processs time-dependent behavior. Dynamic models are appropriate for the transient behavior simulations, though they could also be used to analyze the system behavior under dynamic conditions. The motivation of system for this system simulation was to determine any enhancements to the system for increasing the production of distilled water.
1.4.3 Comparing Results
In this research, the water produced from the solar-powered desalination system was determined by two methods: PV solar-powered system and a solar still.
The methods used were:
3


1. Compare the fresh water results from PV Solar modeling simulation to the results from modeling the solar still.
2. Compare the fresh water results from PV solar experimental approach to the results from the experimental solar still.
1.5 Research Methods
This research will use two different methods for the production of the distilled water. The first method was the photovoltaic solar powered desalination system. Computer software program was used to estimate the production for three types of water systems based on the NIST (National Institute and Standards Technology) fluid properties. MATLAB Simulink was used to simulate the desalination processes, and the SAM software was used to obtain the radiation properties.
The second method was the solar still, which was simulated by using MATLAB
r2016a.
4


CHAPTER II
PROPERTIES OF WATER
2.1 Produced Water
Chemical substances may be found in drinking water supplied from pipe water, but they are not dangerous to humans.
The following table presents a list of chemical substances in drinkable water, and the approximate safe levels (the levels more than the leveTs value in the table may cause a serious trouble) [9],
Table 1 Drinkable water standard of water
Substance Nature of Trouble Level (mg/1)
Chloride Taste and corrosion in hot water systems 200-600
Nitrate Methaemoglobinaemia for infants 50-100
Copper Taste, discoloration and corrosion of pipes, and utensils 0.05-3
Iron Taste and growth of iron bacteria 0.1
Manganese Taste, discoloration, and turbidity. 0.05
Phenolic compounds Taste, particularly in chlorinated water Less than 0.001
Zinc Astringent taste, and sand like deposits 5
Magnesium Hardness taste 30-150 (or up to 250 if sulfate exists)
Sulfate Irritation when combined with magnesium or sodium 250
Hydrogen Sulfide Taste 0.05
5


2.2 Feed Water
Feed water compositions are important for several reasons:
a. They are necessary for the production of physical properties data used for design.
b. To operation the system without scale formation, the compositions of scale constituting ions are important. Seawater may have three times the salinity of brackish water, yet the some ions concentration in brackish water may be higher than seawater and produce more scale.
c. In general, desalination processes, such as reverse osmosis and electrodialysis, are dependent on salinity, and as a result, the membrane process is used with brackish water more than with seawater.
2.2.1 Brackish Water
Brackish water is water that has a higher saline concentration than fresh water but less than seawater.
Brackish water may form from the mixing of fresh water and seawater in bodies such as estuaries [34],
Generally, the make up of brackish water lies between fresh water and seawater. Brackish water could be used safely and used for an environmental advantage for crop irrigation in arid areas.
Technically, the salt concentration of slightly brackish water to brackish is between 500-2000 ppm, and it is only cautiously used for irrigation.
There are some classifications of salty water based on the salt concentration in water. Table 2 shows some of the salt water classifications based on salt concentrations [17],
6


Table 2 Water saline category
Designation Total dissolved salts (ppm) Category
Fresh water <500 Using for drinking and irrigation.
Slightly brackish 500-1000 Irrigation.
Brackish 1000-2000 Using for irrigation with caution.
Moderately saline 2000-5000 Primary drainage
Saline 5000-10000 Secondary drainage and saline groundwater.
Highly saline 1000-35000 Very saline groundwater source
Brine >35000 Seawater
2.2.2 Seawater
Precipitation contains C02 dissolved from air, whose carbonic acid causes the rainfall to be slightly acidic because of the carbonic acid that was formed from C02. As rainwater erodes rocks, acids in the rainfall breaks down the rocks. This process generates ions that flow into rivers, streams and oceans. The most dominant ions in seawater are chlorine and sodium. Together, they form a less than 90% of the dissolved ions in oceans [21], The salinity (concentration of salt in seawater) is about 35 ppt (part per thousand) [8], [13].
In most marine areas, salinity is measured as a total of all the salts dissolved in the water. 35 ppt is not a highly concentrated ratio, but the water in the oceans or seas, which have 35 ppt, is very salty. The interesting characteristic of salt concentrated in water is that the dissolved salts are made up of the same type of minerals and salts, and they always appear in the same concentration ratio to each other (even if the salt concentration is different
7


from the average concentration)^]. The majority of salt in seawater is sodium and chlorine, but other salts exist as well.
Potesium (1.13%)
Salts in Seawater
Figure 2.1 Ions concentration in seawater
Figure 2.1 shows the major ions in seawater[8]. The major ions are those components whose seawater concentration is more than 1 ppm (part per million). The reason for using this definition of major ions is that salinity is reported to 1 ppm [33], Therefore, the major
8


ions are the ones which contribute to the salinity. According to the definition, there are eleven major ions in seawater.
Table 3 indicates those ions and their concentrations (from Pilson, 1998) Table 3 Major ion concentration in seawater.
Ion Concentration (g/kg)
Na 10.781
K 0.399
Mg 1.284
Ca 0.4119
Sr 0.00794
Cl 19.353
S04 2.712
HC03 0.126
Br 0.0673
B(OH)3 0.0257
F 0.0013
Totals 35.169
9


CHAPTER III
DESALINATION
3.1 Desalination Use.
Desalination specifically refers to the removal of minerals and contaminated substances from salt water.
Water sources can include seawater, brackish, rivers and streams, process water and industrial feed, and wastewater. Because of the saline, this water is not appropriate for human usage, and it should be desalinated to use safely. Desalination is already being used internationally for the following reasons:
1. Fresh water scarcity and natural sources cannot fulfill the growing request for low salinity water.
2. The industrial requirement for pure water, such as for petroleum processing and power plants.
3. There is a deterioration of the quality of potable water resources. The rapid decrease of underground aquifers and increase of the salinity concentration in those nonrenewable resources exacerbates the global water deficiency problem.
4. As technologies develop, water desalination becomes easier, and there are many types of desalination processes.
The desalination process has improved rapidly, and it is used by several regions. It is already a satisfactory solution to water scarcity in the world, and it is now approved as a trustworthy resource for fresh water.
According to IDA (International Desalination Association), the number of desalination plants operated in the world in 2015 was 18,426. These plants provided more
10


than 22.9 billion US gallons daily, and supplied fresh water for about 300 million people in 150 countries [1],
At present, about 1% of people in the world are depending on desalinated water to for daily requirements, but according to United Nations, 14% of the people in the world will be suffering from water scarcity by 2025 [2],
Figure (3-1), shows desalination distributions in the world basing to the regions [19],
South America 0.8%
Carribean
3.5% Australia 0.8%
Middle East 49.1%
13.3%
Figure 3.1 Chart shows a fraction of the worldwide capacity of the desalination plants by regions.
11


3.2 Desalination Background
Desalination is a natural phenomenon that has already been occurring on the earth for billions of years. The natural water cycle (water evaporating from the sea and then condensing to form pure rainfall) is the clearest example of the water desalination process. Creek sailors heated water to evaporate fresh water from the saline water. In 1804, the first public water plant built in Scotland by Robert Thom was based on slow sand filtration [5], Since 1960, the worldwide capacity for desalinated water has grown exponentially [3],
The following figure shows the worldwide desalinated water capacity since 1960.
46
Figure 3.2 Installed desalination plants capacity in the USA and worldwide from 1950 to 2006 [3],
12


3.3 Desalination Process Classifications
Desalination is an energy intensive system and involves expensive infrastructures. Thus, several desalination methods have been industrialized over the years to yield potable water from saline water economically. Desalination processes can be classified, based on the separating system that is applied, into physical, thermal, and chemical processes. There are two major types of desalination methods: membrane and thermal.
3.3.1 Membrane Process
The membrane separation process includes the passage of water into a semipermeable film under a pressure. Pressurization reverses the natural transport of water that occurs from a dilute side to a more concentrated side to balance the fluids energy. The membrane process needs driving forces such as electrical potential, vapor, and pressure to overcome the natural osmotic pressures and effectively force water through membrane processes.
The membrane process is subdivided into two types [26]:
a. Reverse Osmosis (RO)
b. Electrodialysis (ED)
Reverse Osmosis is a pressure-driven process. The operating pressure range of RO is from 3.4-68 bar [10], RO was commercially presented in the 1970s, and currently, RO is the largest desalination process method used in the EISA. RO is used for desalinating feed water with a salt concentration more than 15,000 ppm [26],
Electrodialysis is a direct current-driven process. Electrical power is used to transfer the salts ions throughout a membrane, and then separate them to create potable water as a product. ED was commercialized in the 1960s [26], ED was initially considered a seawater desalination method, but it has largely been used for desalinating salty or brackish water.
13


Because of the essential features of the electrical methods used in Electrodialysis systems, ED is typically used to treat brackish water rather than seawater.
3.3.2 Thermal Process
The thermal process technology, as the term indicates, involves heating saline water to its boiling temperature to produce vapor, and then condensing the vapor to obtain fresh water. The thermal process is one of the oldest and most common techniques used. Thermal technologies are used with seawater, but have seldom been used with brackish water due to high costs.
SEA
WATER
ENERGY
I
DESALINATION
PLANT
FRESH
WATER
WASTE
BRINE

t>
Figure 3.3 Thermal desalination process diagram
In the thermal process, thermal energy could be obtained from conventional
hydrocarbon sources or nonconventional solar energy sources. Therefore, the thermal process involves a source of energy to give the system enough power for operation. The source could be a fossil fuel source, or a renewable energy source such as solar power.
14


I. Conventional Hydrocarbon Sources
The thermal process uses fossil fuels to heat saline water and form a vapor. There are many types of desalination processes which use the conventional energy, such as [26]:
a. Multi-Stage Flash Distillation (MSF).
b. Multiple-Effect Distillation (MED).
c. Vapor Compression Distillation (VCD).
Multi-Stage Flash Distillation
MSF is one of the thermal desalination types which has been in use since about the 1950s. MSF facilities involve a number of chambers connected together. MSF is the process which has a stream that flows through a bottom of stages (chambers), with each successive stage operating at a sequentially lower pressure [26], A proportion of the stream of brine flashes into vapor and will be condensed and collected as fresh water. In MSF distillation, feed water is heated in sequenced stages. A MSF plant could contain from 4 to 40 stages [24], [36],
Steam Elector
Condensate Bar* to Baler
Figure 3.4 Schematic diagram of multi-stage flash [36],
15


Multiple-Effect Distillation
The MED is a thermal process method which has been used over 100 years, making it the oldest desalination technique which is still used. The MED desalination technique occurs in series of effects (vessels) and it reduces the pressure in successive steps. In a typical plant, there are from 8 to 16 steps [24], The Multiple-Effect distillation is similar to Multi-Stage Flash distillation, which uses an evaporative technique that occurs in a series of effects or chambers. However, the MED differs from the MSF in which the steam formed in one step condenses in the next one. Also, in a multi-effect distillation, feed water could be sprayed onto a tube bundle or flow onto vertical surfaces to promote a fast boiling and evaporation. Vapor, which is generated in the first step, heats up the second step for evaporation and is condensed in the tubes. These evaporation and condensation processes occur continuously for several steps.
Figure 3.5 Schematic diagram of multiple-effect distillation.
16


Vapor Compression Distillation
The VCD has been used for medium and small scale units, and it is based on the principles of decreasing the boiling point temperature by reducing the pressure. The heat used to evaporate the feed water comes from compressing the vapor. Steam jets and mechanical compression systems are commonly used to condense steam to produce enough energy to evaporate the incoming feed water.
Vapor compression distillation has a comparatively high thermal performance and could be applied in the desalination of highly concentrated salt water. VCD is typically used in medium and small capacity applications. The following diagram provides a simple illustration of the vapor compression desalination system. The VCD is used in combination with another thermal distillation process [24], [11], [36],
Preheated SW
Figure 3.6 Schematic diagram of vapor compression distillation [36],
17


The following figure shows the global desalination capacity distribution according to
the technology that is used.
Figure 3.7 Global distribution of installed water desalination capacity by technology [37],
II. Nonconventional Solar Sources.
Solar desalination or solar distillation is one of the available methods that is currently satisfying global water needs in several regions. Solar desalination is a suitable solution for small communities where sources of electricity are not available, and there is a plenty of solar radiation. Furthermore, solar energy is considered a clean source of power, and it is an environmentally friendly and a highly promising technology. Solar desalination has the advantage of cost savings due to the fact that solar energy is a limitless power source and is easily accessible.
18


Solar energy is an appropriate energy source for water desalination and is currently a popular area of research. Therefore, its important for solar-powered water desalination to be considered in the techniques for salt water desalination. Solar energy is one of a number forms of thermal energy that could be used for providing power for desalination processes. The Performance of solar desalination systems depends upon the design and climate conditions. Several efforts have been made to improve and develop the performance of solar distillation. Solar energy can be used for desalinating water in an indirect way, where the power from a solar energy device system is supplied to a distilled unit, or in a direct way through solar stills.
There are two processes for the solar powered desalination techniques:
a. Using photovoltaic cells to get the enough energy to heat the feed water.
b. Solar stills
Using photovoltaic cells (PV)
The PV system is a simple approach involving the use of PV solar cells to generate enough electricity to supply power to a heating source to heat the feed water. The PV solar desalination technique uses solar energy as an indirect energy source. Photovoltaic cells can convert solar energy to electricity to heat feed water which can then be combined with storage batteries.
Solar Stills
The solar still is one of the solar desalination methods that is used for distilled water from salt water. Solar stills use direct sun radiation to evaporate feed water, and can be used with a large or small system. A solar still may be designed to meet the water needs of a single family, and it is relatively inexpensive systems, especially when used for small groups.
19


CHAPTER IV
SOLAR ENERGY
4.1 Introduction of Solar Energy
Solar radiation is a term for electromagnetic radiation, which is received from the sun. Solar radiation can be converted to useful energy such as electricity or heat.
The Total Solar Irradiance (TSI) depends only on the distance between the sun and the earth and the total sun energy per second (time) [29],
Not all of the suns radiation are absorbed by the earth: 29% of the energy is reflected, and the other 71% is absorbed by the oceans, land, buildings, and atmosphere [42],
4.2 Sun-Earth relationships
The sun is a sphere of hot gasses, and its temperature is 5777 K. The mean distance between the earth and the sun is 1.495 1011 m [29],
The radiation emitted from the sun to the earth is a nearly constant amount, and it is called the solar constant (G) [29],
The solar constant is the energy which is emitted from the sun per a time unit that is receive on the unit area of a surface perpendicular to a direction of the spread of the radiation at the mean earth-sun distance. The absorbed radiation contains visible light and infrared radiation.
According to the World Radiation Center (WRC), the value of the Solar Constant (G) is 1367 w/m2 [29],
The following figure shows the solar constant, and the average distance between the sun and the earth. As well as, the figure 4.1 shows the angle of solar radiation on the earth.
20


Sun 1.27 x 107 m
4.3 Solar Radiation Definition
For engineering purposes, it is important to understand the differences between types of solar radiation such as beam radiation, diffuse radiation, total solar radiation, and irradiance [29],
Beam radiation is received directly from the sun without have been changed by scattering over the earths atmosphere, and it is also referred to as direct radiation. To avoid confusion between the direct solar radiation and diffuse radiation, the term of beam radiation is used [29],
Diffuse radiation is the radiation that is received from the sun after it is scattered by the earths atmosphere. In some meteorological literature, diffuse radiation refers to sky radiation [29],
21


Total solar radiation is a sum of the solar diffuse radiation and the solar beam
radiation on a horizontal surface. Total solar radiation is also known as global radiation [29], Irradiance is the rate at which the radiant energy is incident on a unit area of a surface The Solar radiation which is received from the sun to the earth is a variety with a time of the year. The following figure appears the variation of the extraterrestrial solar radiation with time.
Month
Figure 4.2 Variation of the solar radiation with the year [29],
For engineering purposes, the energy that is received from the sun could be considered constant [29],
4.4 Solar Energy Applications
Solar energy or solar power is a form of energy harnessed from the heat and power of the sun. Solar energy is renewable, and thus a green (eco-friendly) energy source, just like wind power. These green energies are virtually inexhaustible, unlike expendable fossil fuels.
22


However, solar power is reliant upon the weather and the sunshine present in a location. Areas which lack sunlight or experience cloudy weather may have difficulties using solar power effectively.
Fortunately, most areas that suffer from water scarcity are located in regions that have an abundance of sunshine. Every hour, the sun emits enough power to deliver enough energy for a whole year across the globe [45], Solar energy is used to create large amounts of power on a utility scale and to provide individual businesses and residences with electricity.
Because sunlight is available almost everywhere, and it does not require fuel or connection to a power grid, solar energy is useful for providing power to remote regions and for various portable devices.
A common way of harnessing power from the suns rays is through photovoltaic (PV) panels. The PV panels operate as conductors that take the suns lights, heat up, and generate energy (and electricity). Since technologies are developing and the ingredients of the materials used in the photovoltaic panels are becoming greener, the PV technique is becoming more accessible.
Most solar panels that are used today have an average life expectancy of 20-40 years [45], However, solar power generation is not a new technology; it has been used for more than 50 years.
Most of solar energy use is on a small scale, and most of the large-scale generation was developed in the 1970s and 1980s [32],
There are many applications for using the solar energy:
1. Heating residential buildings.
2. Electric power generation
23


3. Water heating uses.
Some areas in the United States are more apt for solar power than others. In 2009, California had the most solar power capacity, followed by New Jersey.
Almost all states in the USA receive sunlight per square mile more than German
[32],
Figure 4.3 Available solar energy in the United States [32],
4.4.1 Suns energy capture ways
Solar rays are distinguished according to their wavelengths. Infrared rays constitute around 50% of light, while the visible light accounts for 40%. The remaining rays are ultraviolet, which make up about 10%. Because most of the infrared rays are short waves, they are not considered warm radiation rays. The wavelength of infrared rays is less than 3000 nanometers [38],
24


Using sunlight in buildings has the potential to significantly decrease energy consumption. This area of development is called day-lighting, and it is one of the methods used to decrease energy consumption in buildings.
Solar energy is easily converted into heat through absorption by liquid, gaseous or solid materials. Heat can then be used in sanitary water heating, water evaporation, and other purposes. Heat can also easily be converted into electricity, and it could run or facilitate physical or chemical transformations.
Solar radiation could also be observed as a flux of photons or electromagnetic particles. Photons that come from the sun are highly energetic, and they could promote photoreactions such as generating electrons conduction in semiconductors or enabling the transformation of sunlight into electricity. Note that the two fundamental approaches to capture the suns energy photoreaction and heat could also be combined in a number of methods to provide combined energy vectors, e.g. electricity and heat. Therefore, from the two basic methods (heat and photoreaction), we can distinguish some main domains of applications such as photovoltaic electricity and thermal power.
Solar cells are made from semiconductor materials. When the sunlight is incident on the PV arrays, it knocks electrons in the PV cells material atoms. As the electrons flow throughout the cells, electricity is generated [32],
Modem PV solar cells were developed in the 40s and 50s from the last century, and the technology has improved over the past years. The space programs of some countries such as the United States use photovoltaic solar cells as an energy source to generate power for spacecraft and satellites [32], PV panels have also been used for supplying electricity to remote areas that lack local electricity, such as arid areas.
25


Solar cells are organized onto the solar panel. This solar panel is coated to protect the solar cells (usually coated on glass). Several panels are organized into an array that can be scaled to give enough energy. A single cell can produce electricity to power an emergency telephone, though larger arrays are needed to power buildings
High transprency PV glass
EVA FILM
(Ethylene Vinyl Acetate)
Frame Aluminum
EVA FILM
(Ethylene Vinyl Acetate)
Solar Cells
Sheet TPT
(Tedlar/PET/Tedlar)
Figure 4.4 Photovoltaic cell panel.
26


CHAPTER V
PROJECT DE SCRIBTION AND ANALYSIS
5.1 PV Solar Powered Desalination
PV Solar Desalination is a simple method which uses a Photovoltaic cell (PV) to generate electricity. The PVs supply enough power for the heating source (heater) to deliver a required thermal energy to boil the feed water to generate vapor and then this vapor is condensed to produce fresh water. The sun radiation is collected by the PV solar cells for producing the electricity which is stored in batteries.
The purpose of using the batteries with this system is to store extra power for use at night or in cloudy days.
Photovoltaic
Panels
Water
Storage
Desalination
Figure 5.1 PV solar desalination system.
27


5.1.1 System Outline
Compared with other desalination systems, the PV Solar desalination has several differences. Because prototyping testing is costly and time consuming, it is difficult to predict the performance of the system.
Therefore, modeling and simulation are important for concept evaluation, prototyping, and analysis of PV solar desalination systems. Furthermore, the modeling process could model not only the thermally simulated modules, but also the embedded software which was used to control all the required components.
MATLAB/Simulink is a general-purpose modeling and simulation package used in science and engineering design and research for the modeling of engineering systems.
MATLAB, Simulink, and Simscape were used for modeling the desalination system. Simscape enables the designer to build models of physical systems in the Simulink environment rapidly. Simscape could also be used to build component models based on a physical connection which directly integrates with other modeling diagrams. Simscape provides a complex component and analysis capability. It also helps to test the system and develop the systems control. The models can be parameterized using MATLAB r2016a expressions and variables [6],
The inputs for running this project after completing the design depend on weather conditions and the amount of feed water. The weather conditions include the suns radiation and the temperature of the day.
To design and test the solar desalination, the PV panel, heat system, and condensate system were modeled in MATLAB r2016a and the Simulink environment. The model was
28


developed using physical principles and empirical data. Emphasis was given on maintain simple component models.
The model was developed to determine the distilled water production from feed water by using Matlabr2016a Simulink/Simscape simulation.
To facilitate the modeling process, the project was divided into four steps to simulate the process.
Develop PV Solar Array and Batteries.
Size Heating Source (Heater).
Provide Heat to the Water.
Vapor Condensing.
The following schematic represents the outline of the system that was designed using MATLAB r2016 Simulink/Simscape.
The design depends on the physical properties of water according to the National Institute of Standard and Technology (NIST) software, which is related to MATLAB r2016a environment software.
Each of the four outlines steps were connected with each other by Simulink blocks obtained from the Simscape library, which was especially useful for simulating thermal fluids. Some data of the components that exist in the MATLAB library were used.
The process (modeling) was arranged with successive steps from the modeling of the photovoltaic system to the production of water.
Simulink models were assembled as connected blocks which were structured hierarchically.
29


simulating of water distillation
Wfer Twiparaturo
vty-f qualrty

-3PO-B
-dlaHg
r
EH3 x~
Fo*f Jti I^'SI r-->^^
heating & evaporate
condensate
Figure 5.2 PV solar powered desalination schematic


5.1.2 Develop PV Solar Array and Batteries
The PV Solar panel was the main component in the solar power system which generated electricity that was stored in batteries. The panels were integrated with charged batteries to give the system stability and continuity. As a result, the production of water was more consistent.
Constant3
Constart4
Voto;e meaa-re Vo|mter
Figure 5.3 PV module and batteries modeling in MATLAB/ Simulink
31


The first step was to determine the Photovoltaic solar module data.
1. For an ideal PV Circuit, the following parameters are used in the model:
Figure 5.4 Ideal PV circuit
I = Ipv-ID [16], [18] h>=*>* [exp (^) l] [16]
(1)
(2)
VT =
Ns KT
[16]
I is the PV output current.
Vxis the thermal voltage
K is the Boltzmanns constant, and it is equal to 1.398 *10"23 J/K. q = 1.602 *10"19 coulomb.
Ns is the PV cells number.
T is the PV cells temperature.
(3)
32


a is modified ideality factor.
Ipv is the current generated by the incidence of light. Io is the diode reverse bias saturation current.
At a short circuit;
I = ISc, and I = Ipv V = 0
At an open circuit; 1=0
V = Voc= aVT*ln (l+^) [16]
2. For an equivalent circuit with series and parallel resistances:
Figure 5.5 Equivalent circuit for PV module
The power output from the electrical circuit is expresses by the relation; P = IV [29]
I = II Id Ish [29]
(4)
(5)
33


V+I*Rs
[29]
(6)
lsh
Rsh
II is the current generated by the incidence of light.
Ishis the shunt current.
Rs is the series resistance.
Rsh is the shunt resistance.
Id is expressed in the same way of the equation (2)
Thus, the circuit needs five parameters to operate (II, Id, Rs, Rsh, and a)
Modified ideality factor a is related to the known physical parameters (k, T, Ns, and q) and the unknown parameter n by the equation [29];
nkTNs
a =
[29]
(7)
n is the ideality factor.
For an ideal diode, n=l.
For real diode, n is between 1 and 2.
The five parameters (II, Id, Rs, Rsh, and a) were obtained by using the measured characteristics of the voltage and current of the module at the reference conditions that are supplied by a manufacturer.
The power-voltage measurements were made at a cell temperature 25 C, incident radiation 1000 W/m2, and spectral air mass equal to 1.5 [29],
The current-voltage measurements at the reference conditions were available from the manufacturer at maximum power, short circuit conditions, and open-circuit conditions. The manufacturer also supplied the temperature coefficient ([1 /, sc) of short-circuit current, and
the temperature coefficient ([IV, oc) of open circuit voltage [29]
34


(8)
II = Sref 0L'ref + SC (X- ^(c.ref))) [29]
Tc is the PV cell temperature.
Tc ref is the PV cell reference temperature.
s
: is the effective absorbed solar ratio.
Sref
S = Sref [29],
The value of the diode current is given by [29];
lo ( Tc V /Eg , _ Eg , \
Io, ref [t(Ci0/ eXpVkT k T 1 Tl .J
Eg is a bandgap energy of a material which is;
Eg/(Eg,ref )= 1- C (T-Tc,ref) [29] (10)
For silicon;
Eg= 1.794 10'19 J.
C= 0.0002677.
The series resistance Rs does not depend on the temperature or the solar radiation; Rs=Rs,ref [29], The shunt resistance Rsh depends on the absorbed solar radiation and does not depend on the temperature;
Rsh/R(sh,ref) =Sref/S [29] (11)
Based on Rauschenbach (1980), the negative inverse of the shunt resistance was approximately equal to the slope of I-V curve at the condition of open circuit voltage.
dl/dV = 1/Rsh [29] (12)
a/a ref = Tc/Tc,ref [29] (13)
The following table presents the PV module electrical characteristics that were obtained from the manufacturer.
35


Table 4 PV solar electrical characteristics
Maximum Power Pmax. 320 w
Vmp 54.7 V
Imp 5.86 A
Voc 64.8 V
Isc 6.24 A
Efficiency 19.6 %
Total number of series cell Ns 96
PV Solar module data for Sunpower SPR-E19-320.
For this project, the data which shows in Table 5.1 were used to design the PV Array, and it was chosen because of the high module efficiency, which was more than 19%.
70
eo
50
40 g
30 % o CL
20 10 0
0 5 10 15 20 25
Voltage (V)
Figure 5.6 Typical P V and I V curve for PV module [29],
For estimating the PV solar panel daily operation, it was important to know the daily peak sunshine hour (PSSH) for the location where the PV Array was installed.
36


PSSH refers to the solar radiation which a particular location could receive if the sun is shining at its maximum rate for a certain number of hours.
The average PSSH in Denver, Co. =5.5 hour/day for fixed tilted array at latitude [41],
The following parameters were used;
The required load energy for operating the desalination system per day is El.
The PV array losses efficiencies are r|.
The PV array thermal factor is Fth.
Then,
El
Peak Power for PV Array (kW) = ------------ [22] (14)
y v 7 PSSH r| Fth L J v '
Equation (14) expresses the power that the PV array should generate for a desalination system that operates with El energy per day.
For estimating the number of PV arrays that is required for systems operating, it should know the power that is generated from the PV array module which was used in the desalination system.
Peak Power for PV Array
Number of PV Array =------- -------------- (15)
PV Module Power
Because of the variations in the PV power resulting from the change in weather, the system could have operational problems.
Thus, the battery storage was necessary to stabilize the energy input to the system, especially when the desired systems operation was longer than the daily peak sunshine hour.
For sizing the batteries, there were two parameters to be estimated: the battery capacity rating (AH) and the battery voltage.
The maximum depth of discharge for battery is DOD [23],
37


Battery Capacity (kW h)
El
(16)
DOD*r|b
[23]
Where; r|b is the battery efficiency.
The output voltage which was required from the battery was Vr.
Thus,
The battery capacity (AH) was given by;
Battery Capacity (kw h)
Battery Capacity (AH) =----------------------- [23] (17)
For the project, the output voltage which was required from the battery was 24 volts. Therefore, the battery capacity could be obtained with only a 24-volt battery or two of 12-volt batteries.
However, using four batteries with 6-volt battery was preferred since the 12-volt, and 24-volt batteries were heavy.
Using more than four batteries might cause an unbalance in the battery charging and discharging.
5.1.3 Size Heating Source
The electric heater was designed as a cylinder around a pipe to generate a uniform heat at a specified temperature.
The initial temperature was the ambient temperature, and a thermostat was designed to limit the heaters temperature.
By controlling the power input to the heater, a uniform heat production of the heater was also obtained. Therefore, the heaters temperature to the feed water was constant with the time.
The following figure is a schematic diagram which illustrates the heater modeling in MATLAB/Simulink.
38


Heater Sizing
Figure 5.7 Heating source sizing in MATLAB/Simulink
The Power comes from the PV Array and Batteries storage assembly. The final
temperature was the temperature which was delivered to heat the feed water.
This heating simulation was built using the following analysis which represents the heat production by the coil heater with a uniform heat generation and a constant temperature.
The cylinder heater has diameter Dh, and length Lh in (m). The heat capacity (specific heat) is Cp.h in (j/kg.C), and the heaters density is p in kg/m3.
The heater surface area, S, was for an open sided cylinder with a thin thickness (th) and given
as: S=7i*Dh*Lh
Thus;
Vol =
it *
Dh ~ (Dh ~ th)2
4
* Lh
(18)
Vol is the heaters volume in m3,
m = p Vol
Where;
(19)
39


m was the heaters mass.
The useful heat which was generated by the heater was Qh,
Qh = m Cp h AT (20)
AT = Th T} (21)
The power inputs to the heater was P, and it was the same power that was delivered by the batteries.
The total heat which was generated from the power P was Q.
Q = P *t (22)
The heaters losses to the ambient was Ls.
Thus,
Q = Qh + Ls (23)
Ls = ha A (Th Ta) (24)
Where;
Th is the heaters temperature.
T; is the heaters initial temperature.
Ta is the ambient temperature.
A is the heaters surface area.
ha is the heat convective coefficient of the ambient air.
Nu Ka
ha = ------- (25)
uh
Ka is the heat conductive coefficient of air.
Nu = 1.15 R*7d (Pr)3 [20] (26)
For Pr > 0.6 [20]
40


Pr is Prandtl number, and Re is Reynolds number.
Re,D = (Va*Dh)/v [29] (27)
Va is the wind speed, v is the air kinematic viscosity.
Thus,
P* t = m Cp h (Th Tj) + haA(Th-Ti) (28)
The Pr, Ka, and v of air are taking according to the bellow table Table 5 Thermophysical properties of air [20],
Temperature (k) v.106 2 m K.103 w (-*) m Pr
100 2.00 9.34 0.786
150 4.426 13.8 0.758
200 7.59 18.1 0.737
250 11.44 22.3 0.720
300 15.89 26.3 0.707
350 20.92 30 0.7
400 26.41 33.8 0.69
Incropera, Frank P.; DeWitt, David P. (2002) 5.1.4 Provide Heat to the Water
Heat that transfers from the heater to the pipe by radiation, and it is expressed by Stefan-Boltzmann law:
Q = Eff AAT4 [20] (29)
Assume the shape factor was equal to one [14],
The heat that transfers between the coil heater and the feed waters pipe was given by
[20];
41


Qrad. (T A
(30)
Where;
g = 5.6703 10"8 is the Stefan-Boltzmann constant.
S is the emissivity coefficient.
Dp is the feed waters pipe outer diameter.
Tp is the pipes outer wall temperature.
The heat that transfers into the pipe to heat the feed water was transferred by conduction and convection.
A. The energy conducted through the pipe was expressed by Fouriers law
Assuming the heat transfer is in one dimension and steady state and has constant properties.
Thus, Fourier law in one dimension is:
Assuming the heat transfers in (r) dimension.
K is the heat transfer conductive coefficient of the pipe
For Quasi-steady state without heat generation for cylindrical coordinates;
q = -K AT [20]
(31)
[20]
(32)
q = -KA- [20]
(33)
[20]
(34)
By solving the above equation, we get;
42


T(r) = Cl In r + C2
(35)
Where;
Cl and C2 are constants.
Solving equation (35) at the boundary conditions,
T(r) = Tpo at r0 and T(r) = Tp; at n.
After solving the values of constants (Cl and C2), the temperature distribution equation in the pipe is;
T(r) =
+ Tpo
(36)
Thus, equation (33) will become
2it Lp K (Tp0 Tpi)
(37)
Tpo, and Tp, are the pipes outer wall temperature, and inside wall temperature. r0, and n, are the pipes outer radius, and inner radius.
Lp is the pipes length.
B. The energy which is transferred by convection from the pipe to feed water is expressed by Newtons law;
Q = hw A AT (38)
_Nu*Kw (39)
AT is the temperature difference between the water before heating and after heating. Kwis waters heat transfer conductive coefficient. hw is waters heat transfer convective coefficient.
A is the pipes inside surface area.
43


D; is the pipes inner diameter.
For calculation Nusselt number Nu, Re must be determined as,
Re =
(40)
Vw is the waters velocity.
vw is the waters kinematic viscosity.
Water flux or water flow rate is equal to water velocity multiplying the areas cross section.
From equation (41), the water velocity Vw is obtained (water flow rate is known). Choosing the tube wetting ratio perimeter for the flow between 0.03-0.14,
wr is the wetting rate, which is the feed water flow rate per pipe unit length.
For laminar flow with a constant surface temperature, the Nusselt number could be estimated as follow:
Nu=3.66 for Re<2300 [20],
For turbulent flow,
Nu = 0.023Re 8 Pr04 for Re>2300 [20],
The required heat energy for evaporating the m mass of water is given by,
(41)
(42)
Qre = mw Cpw(Tb T) + mw L
(43)
Qre is the required energy to evaporate the mass of water.
T is the water temperature in the initial state.
Tb is the water boiling temperature.
Cpwis the water specific heat j/kg.C.
44


L is the latent heat evaporation of water j/kg.
mw is the water flow rate kg/s.
A AAA
Figure 5.8 Schematic of water evaporative in MATLAB/Simulink
The above figure presents the heating water assembly schematic which was simulated in MATALB/Simulink.
The process was simulated in MATLAB/Simulink by using the water properties based on the NIST software.
Two-Phase Fluid Properties (2P)1
Figure 5.9 Two-Phase fluid properties block
The block above was used to determine fluid properties in the MATLAB/Simulink. It provides thermo-physical properties of two-phase fluid. This block parameterizes the properties of fluid in terms of a normalize internal energy and pressure.
45


Un = u min--------1 (From MATLAB)
uLsat(p)-umin
Un is the normalize internal energy, u is the fluid specific internal energy, uLsat(p) is the fluid specific internal energy of the liquid phase at saturated, umin is the minimum internal energy of the fluid in the 2 phase state
Settings
Parameters Liquid Properties Vapor Properties
Minimum valid specific internal energy:
Maximum valid specific internal energy:
Pressure vector:
waterProperty_Tables.u_min kl/kg

waterProperty_Tables.u_max kl/kg

waterProperty_Tables.p MPa
Figure 5.10 Water properties data (picture is taken from MATLAB). The following models the water flow inside the rigid pipe.
I-A-,
o o,0) U. ^ Q
+L
Figure 5.11 Rigid pipe block
The ports A and B represent the inlet and outlet of the pipe. The port H represents the thermal port for the heat transfer between the pipe and the surroundings.
The total thermal energy is equal to the sum of internal energy and kinetic energy.
E = M (ul + i pjSpf) (From MATLAB)
46


E is the total energy of water, ul is the water internal energy, M is the total water mass in the pipe, ml is the water mass flow rate into the pipe through the port A and B (the above equation is from MATLAB).
For understand the evaporation state, it is important to understand the Vapor-Liquid Equilibrium concept.
The Vapor-Liquid Equilibrium (VLE) condition is that the Gibbs energy is minimized at a known pressure and temperature. This means that the Gibbs energy is constant for any small perturbation [44],
(dG)T, p = 0
dG = (Ggw Glw)dnw = 0 [44] (44)
So, Ggw Gw.
Ggw is the Gibbs energy in a vapor (gas) phase, Gw is the Gibbs energy in a liquid phase, and dnw is the small water amount.
When the temperature increases, the water molecules in the liquid phase move more rapidly and it becomes more likely to convert into the gas (vapor) phase. Thus, the pressure of the vapor increases with temperature.
The relation between vapor temperature and pressure is given by Clapeyron equation;
dPsat L
dT TAV
[44]
(45)
AV= Vg Vi
Psatis the saturated vapor pressure. Vg is the volume of the vapor phase. Vi is the volume of the liquid phase.
47


In most cases, Vg is greater than Vi, and for ideal gas pV = RT(treated the vapor as
an ideal gas) [44],
So, the Clapeyron equation becomes;
dPsat L dT T2 R P
[44]
R is the ideal gas constant.
dlnp(T) L(T) dT ~~ T2R
[44]
(46)
(47)
Since 1/p dp= d lnp.
Equation (47) is Clausius Clapeyron equation, which applies at low pressures (less than 10 bar). It is used to calculate the vapor pressure at a given temperature.
A more practical equation that is used for computing the vapor pressure is the Antoine Equation;
lnpsa,(T)= A-^ [44] (48)
A, B, and C are the Antoine parameters for fluid.
Seawater is a mixture of water and several compositions (more than 85% of the mixture is sodium and chloride, as shown in Figure 2.1).
For any seawater component, the partial pressure of any component equals to the vapor pressure of the component multiplied by its mole fraction [44],
Pi = Xj Pi,sat(T) [44] (49)
Pi = y} p [44] (50)
p and pi are the seawater pressure and component partial pressure in the liquid phase.
48


x; and yi are the mole fraction of the component in the liquid phase and the vapor phase in vapor-liquid equilibrium.
Also,
Yi P = Pi,sat (T) [44] (51)
Equation (51) is the Raoults law.
The variable Kvaiue equals to yi / x.
Substitute Kvaiue in Raoults law and rearranged it.
Kvaiue = P',5p(T) [44] (52)
The sum of the all vapor components mole fraction is equal to 1.
Also,
Si yt = 1 [44]
For ideal gas;
Ei lvalue xi 1 [44]
Si Pi = p [44]
(53)
(54)
(55)
For any component, the feed water (F) fraction is z. The heated feed water has a vapor (V) fraction y and residual liquid (L) fraction x.
Fzi = Lxi + Vyi [44]
Substitute Kvaiue value in equation (56).
F Zj = L Xj + V (Kvalue x}) [44]
xi =
Fzj
L + V Kvalue
[44]
Since L= F-V, Then;
(56)
(57)
(58)
49


Xi =
1 + (j) (Kvalue 1)
Since ^jXj 1 and yj J]j KvaiueXj 1 Use the relation (y} x}) = 1 1 = 0. ,
(^value l)^i
(59)
I-
= 0 [44]
(60)
ri + (Kvalue -1)
The above expression is Rachford-Rice equation.
The boiling point of mixture fluid such as seawater is different from the boiling point of pure fluid such as water.
Therefore, the boiling point elevation of seawater is given by the following equation;
R(Tb)2xb
ATh =
[44]
(61)
ATb is the boiling point elevation.
Tb is the normal water boiling point temperature.
xb is the mole fraction of the compositions that exist in the sweater.
L is the waters latent heat evaporation.
R is the ideal gas constant.
5.1.5 Condensing the Vapor.
Condensation is a process in which water vapor is converted to liquid when the temperature of the vapor falls below its saturation temperature.
The condensation process occurs when vapor molecules come in contact with cooler molecules. The vapor will lose energy when the heat transfer of energy occurs and the vapor will convert to liquid. The energy balance of condensate the vapor is the same energy balance for evaporated the water but in the opposite direction.
50


COM fluid
n. 1 ^ 7V,
?r *AMr-*-AVWV-*-AVy-*
1 int^rt) __j_
A}2X rjL 2XtL kj2KrX
Figure 5.12 Heat balance for condensate [20],
The energy that is released from condensation process is expressed by [20]:
Qrel = UA (Too! Too2 ) [20]
qrei is the energy released.
T*)i is the water condensed temperature. T2 is the cooling temperature.
U = R
Ktotal
Rtotai is the total heat transfer resistances.
[20]
R
total

+
[20]
2 it irLpli! 2tt KwLp 2 it r2Lp h2
ri and r2 are the inner and outer pipe radius,
hi and h2 are the heat convective coefficient of water and air respectively.
Nu K
h1 =
Di
[20]
For constant temperature equals and Pr > 0.6.
(62)
(63)
(64)
(65)
51


Nu= 3.66 [20],
h?
Nil Ks
~dT
[20]
(66)
Nu is estimated in the same way in the equation (26).
Nu = 1.15 R*7d (Pr)3 VaD2
PeD
V
(67)
Figure 5.13 Schematic of water condensate in MATLAB/Simulink. The Raoults law is expressed by [44];
ZiXi = 1 (69)
Also, considering the following equation.
52


(70)
Zir!_=1 [44]
lvalue
Replace pi.sat(T) in the Antoine equation (equation (48)):
So, Antoine equation will become;
Pi,sat(T)= 10a"tTc [44] (71)
Substituting the above equation into Raoults law (equation (68)) to estimate the condensation temperature, and this condensation temperature is used to calculate the saturated pressure pi.Sat(T).
Finally, the condensate mole fraction is given by,
Xi
Yi Pi,sat(T)
[44]
(72)
5.2 Solar Still
The basic principles of solar still distillation are simple but effective, as the sun's energy heats the feed water to the point of evaporation. As the water evaporates, this vapor rises and condenses on the solar stills cover for collection. This process eliminates impurities such as minerals, and removes microbiological organisms. The result is fresh water. Thus, the solar stills desalination process uses the suns radiation to evaporate the salt water and then condenses it. The clean water is collected as drinkable water. Modeling was used to predict the operation of the thermal system design for the solar still desalination process.
5.2.1 Solar Still Elements
The essential elements of Solar Still are:
1) Feed water basin.
2) Incoming radiation.
53


3) A transparent cover (glass or plastic).
4) Collection pipes that collect the condensate water.
5) Other miscellaneous parts such as sensors
The suns radiation heats the water in the basin and evaporates the water. The water then condenses under the transparent cover as droplets. These droplets flow down into the collecting pipes
Distillate
or
condensate
through
Sasic elements in a solar still
1) Incoming radiation (energy)
2) Water vapor production from brine
3) Condensation of water vapor (condensate)
4) Collection of condensate
Colection of condensate
Figure 5.14 Solar still basin
5.2.2 Energy Balance
To model the energy balance of the solar still, the following process was followed. The sunlight passes through the cover of the still and is absorbed in the seawater layer and by the black cover in the basin, heating the basin and seawater. Also, the seawater is heated by
54


the black surface by conduction heat transfer. As a result, the seawater temperature increases. Vaporization will take place on the surface of the seawater. The seawater surface is semi-permeable which that means the mass flux of one component is zero. For example, the water that evaporates from the surface evaporates into an adjoining air stream. Therefore, the saturated air at the interface is transported by diffusion because of the partial pressure differences and by convection because of the natural convection of the air from the feed water interface into the air inside the basin. Based on a quasi-steady state energy balance, the air inside the basin is also saturated. Thus, the saturated air inside the basin will condense at the cover.
5.2.2.1 External Heat Transfer
The external energy balance on the solar still includes the cover and the basin bottom losses. Assume there is no temperature gradient along the cover.
Figure 5.15 Overall energy balance
I(t) = I(t)Rg + I(t)ag + I(t)Rw + I(t)aw + I(t)ab (73)
I (t), aw, Rw, ag, Rg, and ab are the solar radiation intensity, water absorptivity and reflectivity, the glass cover absorptivity and reflectivity, and basin bottom absorptivity.
55


I(t) g T ( Qew 1" Qcw T Qrw ) (^Irg + ^icg) [39]
(74)
I(t) aw = mw Cpw + qew + qcw + q. w qb [39]
(75)
(76)
Where;
Cpw is water specific heat capacity. mw is the distilled water mass.
qb is the basin heat transfer, qcb is the basin bottom heat losses, and qs is the heat losses from the side.
The heat losses from the solar still occur on the cover, the bottom, and sides to the ambient by convection, radiation, and conduction.
The heat losses from the solar still that occur on the cover, the bottom, and sides to the ambient are by convection, radiation, and conduction.
I. Losses from the cover:
The covers losses are by convection and radiation.
Convection heat transfer losses from the cover to the ambient is given by,
qcg hcg(Tg Ta) [39]
(77)
Ta is the ambient temperature.
Tg is the glass cover temperature.
hcg is the glass cover heat transfer convective coefficient.
Radiation heat losses are given by [39],
qrg hrg(Tg Ta) [39]
(78)
hrg is the heat transfer radiative coefficient.
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[39]
(79)
hrg
((Tg)4 (Tsky)4) T T
lg
Tsky is the sky temperature which is given by [28],
Tsky = 0.0552(Ta)15 [28]
8 is the glass cover emissivity. o is the Stefan-Boltzmann constant.
The overall glass heat transfer by radiating and convection is qg.
Qg = htg(Tg Ta) [39]
Qg Qcg T qrg [39]
And;
(80)
(81)
(82)
htg = hcg + hrg [39] (83)
Where;
htg is the total heat transfer losses coefficient from ambient to glass. It expressed according to J. H. Watmuff, 1977.
htg= 2.8 +3Va [31], [15]
(84)
II. Losses from the bottom and sides:
Losses from the bottom and sides are by radiation, conduction, and convection.
Qbs = Qb + Qcb + qs Qbs = U0(Tb Ta)
(85)
(86)
qbs is the total losses from bottom and sides.
Tb and Ta are the temperature of the basin and ambient respectively. Uo is the basin overall heat loss coefficient.
U0 = ub + Ue
(87)
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Where;
Ub and Ue are the heat loss coefficient of bottom and sides respectively.
Uh =
(hj + (hb)
[39]
(88)
hb =
1
Lins _|_ hcb f hrb ^ins hcbhrb
[39]
(89)
Where;
Lins and Kins are the stills insulation thickness and thermal conductive coefficient, hcb and hrb are the basin heat transfer convective and radiative coefficient.
On the bottom, there is no wind speed, thus, hcb+hrb=htb and it estimated such as equation (84) with wind speed is zero. Therefore, hcb+hrb= 2.8 w/m2 hw is the water heat transfer convective coefficient.
The Nusselt number inside the still between the water and glass cover is given by Dunkle
[30], [43],
Nu = C(Gr Pr)n [30], [43] (90)
C and n depend on the Gr.
C=0.21, n= 1/4 for 104 < Gr < 3.2 105
C=0.075, n=l/3 for 3.2 105 < Gr < 107
Gr is Grashof number and is expressed by,
Gr =
gBAT (Lb); v2
[20]
(91)
B, g, Lb, and v are the volumetric coefficient of expansion, gravitational constant, space between the glass cover and water, and the kinematic viscosity respectively.
58


AT = (Tw Tgi)
Pr = v/aa [20]
aa is the thermal diffusivity.
Ue=Ub(^) [39]
(92)
Ab and As are the basin bottom area and the basin side area.
With As Ab, the Ue was ignored [39],
5.2.2.1 Internal Heat Transfer
Internal energy balance means that the heat transfer occurs inside the solar still between the feed water surface and the cover by radiation, convection, and evaporation [39], Figure 5.14 shows the model of the distilled water in a typical solar still I. Irradiative heat transfer
The rate of heat radiation from the water surface to the cover is,
q, w hrw(Tw Tg) [39]
(93)
hrw is the irradiative heat coefficient, and it is given by [39],
[39]
(94)
The effective emissivity is given by,
1
[39]
(95)
sw and sg are the water and the glass cover emissivity.
II. Convective heat transfer
The general convective heat transfer equation is given by,
qCw hcw(Tw Tg) [28], [39]
(96)
59


hcw is the heat convective coefficient between the basin bottom and ambient, and it is given by [30],
hcw = 0.884
(Tw Tg) +
'(Pw-Pg)(Tw + 273.15)' , 286.9 103 pw ,
Where,
pw is the partial pressure at the water surface. pg is the partial pressure at the glass cover.
III. Evaporative heat transfer
The general evaporative heat transfer equation is given by,
qew = heva(Tw Tg) [39]
(97)
25.317-(^i^) pu = e v Tw > [28], [39] (98)
25.317-(^idl) [28], [39] (99)
pg = e v 1
(100)
heva is the evaporative heat transfer and it is given by (based on Dunkles) [30], [39],
heva = 16. 273 10-3hcw (y *gJ [30], [39] (101)
The hourly yield is given by [18];
m = * 3600 [18] (102)
Where;
m is the hourly distilled water from the solar still.
L is the latent heat vaporization.
The overall heat coefficient loss between the glass cover and water surface given by;
htw = hrw + hcw + heVa [39] (103)
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Solar still overall loss (U) is given by following equations [39];
u = ut + ub
Ut the solar stills top overall losses.
1
u'=s;
l l
Rt = r- + r-
ntw ntg
Thus,
Ut =
htvvhtg htw T htg
The water temperature Tw is given by [39];
Tw = [1 exp(aa t) + Two exp(- aa t)] aa
Where, f is a function, and it is given by;
f = (t)eff.I(t)+UTa
mC
pw
The value of (ax)eff is obtained from the following equation.
[39]
(ax)eff. = ab
+ aw + aD
*tw
hw + hh w 8 htg + htw
[39]
*w 1 b
Where;
aa is constant and equal to U/(mw* Cpw).
Two is the initial basin water temperature at time t=0
The glass temperature is assumed to have no gradient and expressed by [39];
I(t)ag + htwTw + htgTa
T = lg
htw T htg
[39]
Where;
(104)
(105)
(106)
(107)
(108)
(109)
(110)
(111)
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Tw is the water temperature.
Tgis the glass cover temperature.
For the theoretical calculation, assume there is no temperature gradient in the glass cover and water.
The following figure represents the modeling of the solar still desalination system that was designed using MATLAB r2016 Simulink.
Figure 5.16 Schematic of solar still desalination
62


CHAPTER VI
RESULT
In this section, it will show the simulated results which were developed by MATLABr2016a and compare the simulation with the experimental results of the project. Also, a comparison is made between the several solar desalination processes.
6.1 PV Solar Powered Desalination Results
The simulated results for the Photovoltaic Array were based on the information from Sunpowers Company for their SPR-E19-320 module. The following figures show the relation between the output power with the voltage (P-V Curve) and the Ampere-Voltage relation (I-V Curve).
P-V Graph
Figure 6.1 P-V curve characteristic
63


Figure 6.1 illustrates the relation between the power output from the PV Solar and Voltage.
The maximum power output (Pmax.) occurs at the voltage (Vmp.) and Current (Imp). For this module,
Pmax. =320.27 W at the Vmp = 54.6.
I-V Graph
Figure 6.2 I-V curve characteristic.
As seen in the following figure, Voltage (Vmp.) occurs at a Current Imp=5.86.
Pmax-= Imp Vmp [29] (112)
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The following figure shows the relationship among the Pmax, Imp-, and Vmp, for a PV
Array.
Photovoltaic charcteristic
Figure 6.3 PV Array characteristics for P-V and I-V curves
The above figures are based on a 1000 irradiance. However, the solar irradiance is not constant throughout the day.
Figure 6.4 shows the PV Array characteristics for three irradiance values 1000, 500, and 100^. In this project the theoretical calculations used the maximum operating point characteristics for estimating the output power.
65


I-V Graph
V (volt)
0 10 20 30 40 50 60 70
V (volt)
Figure 6.4 Photovoltaic panel characteristics for different irradiance values (1000,
500, and 100)
The following figure shows the PV Solar output power for an average June day in Denver, Colorado, USA. The values for that day were obtained from the System Advisor Model (SAM) program. It is clear that the actual power output from the PV solar was not adequate to give the required estimated power of 320 W. Thus, using more than one PV panel was needed to provide the required power. In this project, three PV panels were used
66


Power in day (W) e Power in day (W)
Power in day
6.5 Actual power output in June in Denver for one PV panel.
Power in day
Figure 6.6 Actual power output in June in Denver for three PV panels
67


From figure 6.6, it is clear that the PVs Array does not provide enough power to operate the system from about 6 pm to 8 am. Therefore, batteries were needed to keep the system working continuously. The batteries were charged from the PV during the period from 8 am to 6 pm and discharged from 6 pm to 8 am. to give the system the continuous required operating power.
The distilled water obtained from the piped water, heavy water, and sea water are shown in the following figures.
In the figures for the distilled feed water, production flow rate was for a sample of 6 minutes.
The distilled water was measured in kg/s or (liter/s) and with time in seconds.
Water Production
Figure 6.7 Water distilled flow rate for Piped Water.
As shown in the above figure the production started after about 50 seconds. Initially, the distilled water flow rate was high and then decreased over time. The reason for the initial
68


high value was that the condensation pipe at the beginning of the operation was not warm and because of the vacuum pressure that occurred during the starting of the distillation process. Thus, this initial period was neglected in estimating the production of the water.
Figure 6.8 shows the vapor and water temperatures inside the heating and condensation pipes.
Figure 6.8 Vapor-Water distilled temperature for Piped Water.
In Figure 6.8, the difference in temperature between the vapor (red line) and the water distilled (blue line) at the beginning of production was the largest. Also, the difference in the temperature of the water and vapor throughout the period when the unstable production occurred was zero. Therefore, the vacuum pressure caused the unstable production.
69


The system stabilized after about 70 seconds and started to give stable distilled water. Figure 6.7 shows the uniform system flow rate measured in kg/s. The production of uniform
water was the goal of using this system which was connected to batteries.
Vapor Quality
after heating after condcn
sate


/
/

0 50 100 150 200 250 300 350
Time (seconds)
Figure 6.9 Piped Water vapor fraction.
Figure 6.9 shows the ratio of the vapor after heating and condensation process. The red line refers to the vapor ratio after the heating process while the blue line refers to the vapor ratio after condensation process.
The production for one hour is shown in the figure 6.10.
Droduct

1.843
Product (liter)
Figure 6.10 Piped Water distilled production in one hour.
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The amount of production of uniform distilled water is shown in figure 6.11. The
amount of water was about 1.843 liters per hour.
Water Production
Figure 6.11 Piped Water distilled curve.
For heavy water, the feed water was preheated.
Water Product
<5 0 007
W)
3
S3
u
£ 0.005 0
£
Time (seconds)
Figure 6.12 Heavy Water distilled flow rate.
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440
Vapor-Water Temperature
hot vapor distilled water
^400
w
0
u
3 380
c3
320
0 50 100 150 200 250 300 350
Time (seconds)
Figure 6.13 Vapor and water distilled temperature for heavy water.
As seen in the above figure, the temperature of the water distilled was the same temperature of the vapor which means the system was operating in the vapor-liquid equilibrium (VLE) zone.
The water distilled in one hour was about 1.773 liters.
Product (liter)
Figure 6.14 Heavy Water production in one hour.
The heavy water distilled curve was also uniform and is shown in the following
figure.
72


Water Production
0 500 1000 1500 2000 2500 3000 3500
Time (seconds)
Figure 6.15 Heavy Water distilled curve.
Vapor Quality
i ~ -after heating -after condensate-

r
r





0 50 100 150 200 250 300 350
Time (seconds)
Figure 6.16 Heavy water vapor fraction.
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The vapor fraction was uniform for the heavy water desalination.
The seawater desalination behavior was similar to the previous water desalination types. The distilled sea water flow rate was less than the other, which resulted from its higher boiling temperature.
Tbb = ATb+373.15.
Tbb is the seawater boiling temperature, and ATb is the boiling point elevation (the difference between normal water boiling temperature and seawater boiling temperature).
ATb =0.5942 Thus, Tbb = 373.74
Sea water distilled production flow rate was constant with the time.
Distilled Water Flowrate
time(sec)
Figure 6.17 Seawater distilled flow rate.
74


From the above figure, it can be seen the time to start the desalination production was longer than for the piped and heavy water. The reason for this delay is that the seawater consists of more compositions than the piped and heavy water.
The hourly production was 1.409 liters per hour.
Water Distilled in 1hr
Figure 6.18 Seawater distilled production in one hour.
The distilled water curves for piped water, heavy water, and seawater per hour are a linear relation, and the expression could be written mathematically as,
Y= C (X-td)
Where;
td is the time when the distilled starts.
C is a constant.
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Table 6 Feed water types yield
Feed Water Desalination starts Time (s) Yield water per hour (liter)
Piped water 50 1.843
Heavy water 64 1.773
Seawater 107 1.409
For piped water, the boundary condition at X= 3600 and Y= 1.843 C= 1.843/(3600-50) = 0.00519.
And for heavy water, the boundary condition at X=3600 and Y=1.773 C=l.773/(3600-64) = 0.00501
And for seawater, the boundary condition at X=3600 and Y= 1.409 C= 1.409/(3600-107) = 0.00403.
water distilled comparing
3
2.5
I 2
! 1.5
1
0.5
0
Piped water Heavy water Seawater
0 500 1000 1500 2000 2500 3000 3500
time (5)
Figure 6.19 comparing modeling results of water distilled from three water types.
The experiment was done for seawater, and the results are shown in the following figure.
76


distilled water

X 1.8 1.6 ? 14 Il2 i 1 1 -8 1 0.6 0.4 A A


Linear (distilled water)
0.965 ^
0. 8 >
0.553 ^^
0.407
0.1 171^
^OMOj39^ n
0 600 1200 1800 2400 3000 3600
tune (s)
Figure 6.20 Distilled Seawater production done experimentally in one hour.
The experimental water production had an approximate linear behavior. There was a difference between the theoretical solution of the distilled water production which was obtained from simulation of the MATLAB software and the experiment. This difference was because the software simulation had the assumption that the weather conditions such as constant wind speed and temperature during one hour, while in actual testing, there were differences in the weather conditions during one hour. The difference in wind speed was not taken into account in the numerical estimation. The average wind speed was taken as 5 m/s. The distilled water from the experiment was about 1.19 liter per hour.
The following figure shows the difference between the modeling and experimental distillation of seawater. It shows a small difference in the linear relation for the production of
77


water. Both production curves might be more similar if the testing had been done indoor without the effects of wind.
experiment
rm doling
0 600 1200 1SOO 2400 3000 3600
time(s)
Figure 6.21 Comparing fresh water productivity for Seawater from experiment and modeling ofPV solar method.
6.2 Solar Still Results
The data used in theoretical calculation which was made by the MATLAB simulation were taken from 8 am to 5 pm.
The calculation does not estimate the data from 5 pm to 8 am since there was not enough solar energy available. It was assumed that there was no temperature gradient throughout the cover due to a small thickness of the cover. The testing was done for sea water only.
78


water
Figure 6.22 Solar Still modeling yield.
From the above figure it can be seen that the distilled water increased with time until it reached a peak value, and then decreased. The reason for the increase was that the solar energy was increasing in the morning and that led to an increase in the water production, while in the afternoon there was a decrease in production according to the change in solar energy.
When the solar energy was increasing, the energy absorbed by the system increased, which led more heat transfer to the feed water. This increased heat transfer consequently increased the water temperature, causing the rate of evaporated water to increase, resulting in
79


an overall increase in distilled water. Increasing the difference between the water temperature and cover temperature led to an increase in the distilled water.
Figure 6.23 Water temperature and glass temperature.
For the experiment, reference data was taken as, Experiment time is from 9 am to 4 pm.
Feed water depth in the basin=l cm.
Glass cover slope = 38 degrees.
The basin box was 2 m length and 0.5 m width;
Area of the basin =2*0.5=lm2.
The glass cover area was 1,4m2.
80


The glass cover thickness was 4 mm.
There was no temperature gradient through the cover due to the small thickness. The experiment was done on a cloudy day.
distilled water
0
9 10 11 12 13 14 15 16 17
time
Figure 6.24 Reference experimental Solar Still distilled water [40],
The distilled water in this reference experiment fluctuated due to fluctuation in the weather conditions during the experiment. The data taken was in (ml) per hour
6.3 Comparing the results
Comparison of the modeling results of the PV solar powered desalination approach and Solar Still approach are given in the figure 6.25, and the comparison of the experimental results of the both approaches are shown in the figure 6.26.
The mass of the feed water used in the solar still approach was constant; mf = 0.01 m 1 m2 = 0.1 m3.
= 10 liters.
81


While, the feed water flow rate in the PV powered desalination approach was 0.018
kg/s.
rhf =0.018 kg/s 3600 s/hr= 64.8 kg/hr. = 64.8 liter/hr. in one hour.
water
Figure 6.25 Comparing the freshwater results from the PV solar modeling approach with the freshwater from Solar Stills modeling for Seawater.
The modeling of the distilled water of PV-powered approach was done in the same period that the modeling of the solar still was done (8 am to 5 pm). It can be seen that the two approaches have a different behavior with time. The water production from the PV powered system method was not affected by ambient conditions because it was connected to the batteries, which compensated for the solar energy available. On the other hand, in the solar still method, the systems capacity was affected by change in the solar energy available.
82


In the experiment, the difference between the two approaches was observed. The experiments for both methods were done in the same weather conditions.The experiments were made in a cloudy day to study the systems performance.
1.4
1.2
c l
| 1
Â¥ 0.8
"O ,
g,06
£
g 0.4 0.2 0
10 11 12 13 14 15 16
hr
Figure 6.26 Comparing the freshwater results from the PV solar experimental approach with the freshwater from Solar Stills experimental for Seawater.
As seen in the above figure, each approach had difference results. The difference
between the two methods was caused by a variation in the weather conditions during the day.
It can also be seen that the fresh water production from the PV-powered desalination method
was approximately linear and gave a steady daily production, while the solar still daily
production fluctuated with the time due to the weather conditions.
Experiment result







83


CHAPTER VII
DISCUSSION AND CONCLUSION
7.1 Discussion
In this research project, the numerical analysis of the basic solar desalination approaches was established and the theoretical results were compared with results obtained from the experiment.
Using the results from this research, the following could be concluded:
The essential factor affecting the productivity of the solar still was the available solar energy. The water from the solar still increased in proportion to the amount of available solar energy. The performance of the PV solar-powered desalination method was not affected by the variation of solar radiation, because it was connected to batteries to compensate the variation in available solar energy. When the temperature differences between the water interface and the glass cover in the solar still increased, the amount of the fresh water production increased.
The maximum amount of the fresh water obtained from the solar still occurred during the period when the solar radiation was highest, while the distilled water from the PV solar method was approximately constant.
The deviation between the experimental and theoretical results for the solar desalination was due to the following reasons. The equations that were used in the calculations did not consider the heat losses due to the saturated water leakage from the solar still. When the vapor pressure in the solar still was more than the ambient pressure, the saturated air leaked to the outside. The incoming air from the surroundings to the still was not saturated and it took time to be heated and then saturated. This led to a reducution of the
84


distilled water of solar still. This was not considered in the numerical solution that predicted the production rates. And the numerical calculations of the PV solar approach did not consider the changes in wind speed during the one hour testing period.
7.2 Conclusion
Using the PV solar desalination system could provide a steady quantity of drinkable water for a small community and for people who live in regions with impure water sources. Additionally, communities having difficulty in accessing local electricity or a lack of electrical power would benefit from solar desalination. Also, the PV solar desalination was a continuously operating system throughout the day and it could be running continuously throughout the year.
7.3 Future Direction
This research represents a basic step and study towards the development of a solar desalination system. In the future, the study should consider the following points:
Scaling the systems to increase the water flow rate produces from the system.
Determine the systems efficiencies.
Calculate and comparing the systems cost.
85


REFERENCES
[1] "Desalination by the Numbers," International Desalination Association, [Online], Available: http://idadesal.org/desalination-101/desalination-by-the-numbers/. [Accessed 28 January 2017],
[2] "Desalination industry enjoys growth spurt as scarcity starts to bite," Global Water Intelligence, [Online], Available: https://www.globalwaterintel.com/desalination-industry-enjoys-growth-spurt-scarcity-starts-bite/. [Accessed 26 January 2017],
[3] "Desalination: A National Perspective," National Academy of Sciences Press, Washington, D.C., 2008.
[4] "Drinking Water Sources, Sanitation and Safeguarding," The Swedish Research Council Formas, 2009.
[5] "History of water treatment," Lenntech, [Online], Available: http://www.lenntech.com/history-water-treatment.htm. [Accessed 27 January 2017],
[6] Math Works, "Simscape/ Model and simulate multidomain physical systems," Math Works, 2016. [Online], Available:
https://www.mathworks.com/products/simscape.html. [Accessed 5 January 2017],
[7] "National Weather Service, Sea Water," US Dept, of Commerce, National Oceanic and Atmospheric Administration, [Online], Available:
http://www.srh.noaa.gov/srh/jetstream/ocean/seawater.html. [Accessed 9 January 2017],
[8] "Ocean Health-Chemistry of Sea Water," Ocean plasma, [Online], Available: http://oceanplasma.org/documents/chemistry.html. [Accessed 7 February 2017],
[9] "Physical and Chemical examination," in European Standards for drinking-Water, 2nd ed., Geneva, World Health Organization, 1970, pp. 36-37.
[10] "Water Desalination Processes," American Membrane Technology Association (AMTA). ,2016. [Online], Available:
http://www.amtaorg.com/Water_Desalination_Processes.html. [Accessed 28 January 2017],
[11] "Water Desalination using Renewable Energy | Technology Brief," 2012. [Online], Available:
http://www.irena.org/DocumentDownloads/Publications/Water_Desalination_Using_ Renewable_Energy_-_Technology_Brief.pdf. [Accessed 5 February 2017],
[12] "Water Scarcity, water & poverty, an issue of life & livelihoods," FAO Water, 2015. [Online], Available: http://www.fao.org/nr/water/issues/topics_scarcity_poverty.html. [Accessed 12 January 2017],
86


[13] "Why is the ocean salty?," National Ocean Service, National Oceanic and Atmospheric Administration U. S. Department of Commerce, [Online], Available: http://oceanservice.noaa.gov/facts/whysalty.html. [Accessed 5 February 2017],
[14] [Online], Available: http://www.cfdyna.com/Notes/ViewFactors.pdf. [Accessed 6 January 2017],
[15] B. D. Gupta, T. K. Mandraha, P. j. Edla and M. Pandya, "Thermal Modeling and Efficiency of Solar Water Distillation: A Review," American Journal of Engineering Research (AJER), vol. 02, no. 12, pp. 203-213, 2013.
[16] D. Bonkoungou, Z. Koalaga and D. Njomo, "Modelling and Simulation of photovoltaic module considering single-diode equivalent circuit model in MATLAB," International Journal of Emerging Technology and Advanced Engineering, vol. 3, no. 3, pp. 493-502, 2013.
[17] D. Hillel and E. Feinerman, "Salinity Management for Sustainable Irrigation: Integrating Science, Environment, and Economics," The International Bank for Reconstruction and Development/ The World Bank, Washington D.C., 2000.
[18] D. Mowla and G. Karimi, "Mathematical modelling of solar stills in Iran," Solar Energy, vol. 55, no. 5, pp. 389-393, 1995.
[19] DAVID H. MARKS et al, Committee to Review the Desalination and Water Purification Technology Roadmap, Washington, D.C.: THE NATIONAL ACADEMIES PRESS, 2003.
[20] F. P. INCROPERA, D. P. DEWITT, A. S. LAVINE and T. L. BERGMAN, Fundamentals of Heat and Mass Transfer, Hoboken: John Wiley & Sons, Inc., 2011.
[21] G. Anderson, "Seawater Composition," Marine Science, 8 October 2008. [Online], Available: http://www.marinebio.net/marinescience/02ocean/swcomposition.htm. [Accessed 28 December 2016],
[22] G. E. Ahmad and J. Schmidb, "Feasibility study of brackish water desalination in the Egyptian deserts and rural regions using PV systems," Energy Conversion and Management, vol. 43, no. 18, p. 2641-2649, 2002.
[23] G. E. Ahmed and M. A. Mohamad, "Use of PV systems in remote car filling stations," Energy Conversion & Management, vol. 41, no. 12, pp. 1293-1301, 2000.
[24] H. Cooley, P. H. Gleick and G. Wolff, "DESALINATION, WITH A GRAIN OF SALT A CALIFORNIA PERSPECTIVE-Appendix A," PACIFIC INSTITUTE, Okland, 2006.
[25] H. Ettouney, "Conventional Thermal Processes," in Seawater Desalination, Springer Berlin Heidelberg, 2009, pp. 17-40.
87


[26] H. J. Krishna, "Introduction to Desalination Technologies," [Online], Available: http://www.twdb.texas.gov/publications/reports/numbered_reports/doc/r363/cl.pdf. [Accessed 24 January 2017],
[27] H. Perlman, "The USGS Water Science School-The World's Water," USGS, 2 December 2016. [Online], Available: http://water.usgs.gov/edu/earthwherewater.html. [Accessed 1 January 2017],
[28] I. U. Haruna, M. Yerima, A. D. Pukuma and I. I. Sambo, "Experimental Investigation of the Performance," INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH, vol. 3, no. 3, pp. 169-174, 2014.
[29] J. A. Duffie and W. A. Beckman, Solar Engineering of Thermal Process, Hoboken: John Wiley and Sons Inc., 2013.
[30] J. C.-d.-G. M. A. P.-G. J C. Torchia-Nunez, "Thermodynamics of a Shallow Solar Still," Scientific Research Publishing Inc., vol. 6, pp. 246-265.
[31] J. H. Watmuff, W. W. Charters and D. Proctor, "Solar and wind induced external coefficients Solar collectors," Revue Internationale d'Heliotechnique, vol. 2, p. 56, 1977.
[32] J. Hamilton, "Careers in Solar Power," U.S. Bureau of Labor Statistics, June, 2011.
[33] J. Murray, Chpt 4: Major Ions Of Seawater, University of Washington: Lecture, 2004.
[34] L. D. Paulson, "What Is Brackish Water," RWL Water, 29 September 2014. [Online], Available: https://www.rwlwater.com/brackish-water/. [Accessed 28 December 2016],
[35] LINDASTCYR, "WORLD WATER DAY: 10 PLACES MOST IN NEED OF CLEAN WATER," ecorazzi, 22 March 2012. [Online], Available:
http ://www. ecorazzi. com/2012/03/22/world-water-day-10-places-most-in-need-of-clean-water/. [Accessed 30 December 2016],
[36] M. A. Eltawil, Z. Zhengming and L. Yuan, "RENEWABLE ENERGY POWERED DESALINATION SYSTEMS: TECHNOLOGIES AND ECONOMICS-STATE OF THE ART," in Twelfth International Water Technology Conference, IWTC12 2008,, Alexandria, Egypt, 2008.
[37] M. G. Buonomenna, "Membrane processes for a sustainable industrial growth," The Royal Society of Chemistry, vol. 3, no. 17, pp. 5694-5740, 2013.
[38] M. van der Hoeven, Solar Energy Perspectives, INTERNATIONAL ENERGY AGENCY, 2011.
[39] O. O. Badran and M. M. Abu-Khader, "Evaluating thermal performance of a single slope solar still," in Heat and Mass Transfer, Verlag, Springer, 2007, p. 985=995.
88


[40] P. i. ALKAN. (2003). Theoretical and Experimental Investigations on Solar Distillation of IYTE Giilbah9e Campus Area Seawater (Unpublished masters thesis).izmir Institute of Technology, Izmir, Turkey.
[41] R. A. Messenger and J. Ventre photovoltaic Systems Engineering, 2nd ed., Boca Raton; London; New York; Washington, D.C.: CRC Press LLC, 2004.
[42] R. Lindsey, "Climate and Earths Energy Budget," NASA, 14 January 2009. [Online], Available: http://earthobservatory.nasa.gov/Features/EnergyBalance/page4.php. [Accessed 11 February 2017],
[43] R. V. Dunkle, "Solar water distillation: the roof type still and a multiple-effect diffusion still," International Development in Heat Transfer, vol. 5, pp. 895-902, 1961.
[44] S. Skogestad, CHEMICAL AND ENERGY PROCESS ENGINEERING, Boca Raton: CRC Press, 2009.
[45] Susan, "Shine On: An Introduction to Solar Power," Just Energy, 20 June 2013. [Online], Available: http://www.justenergy.com/blog/shine-on-an-introduction-to-solar-power/. [Accessed 7 February 2017],
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DISS_para This dissertation presents theoretical analysis and simulations used to improve the performance of desalination systems and compares several solar desalination processes. This research demonstrates how to use modular approaches for the dynamic simulation and steady state analysis of desalination by using MATLAB r2016a Simulink. Data from NIST (National Institute of Standard and Technology) and from SAM Advisor (System Advisor Model) were used in this study. Three types of distilled water (pipe water, heavy water, and seawater) were used to compare the distilled fresh water produced from each solar desalination system. The potable water production rate from heating the feed water was calculated using empirical and theoretical modeling. Results of the modeling and experimental results were compared for both processes. The simulations, modeling, and optimization of desalination processes using computer design technology are discussed. The results from this research could be used to predict the operating conditions of desalination systems.
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AN ANALYSIS AND SIMULATION OF SOLAR WATER DESALINATION SYSTEMS b y AHMED GHADHBAN B.S., University of Basrah, 2005 A t hesis submitted to the Faculty of the Graduate School of the University of Colorado in partial fulfillment of the requirements for the degree of Master of Science Mechanical Engineering Program 2017

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ii This thesis for the Master of Science degree by Ahmed Salim Hial Ghadhban has been approved for the Mechanical Engineering Program by Peter Jenkins, Chair Kannan Permnat h Maryam Derbeheshti Date: May 13, 2017

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iii Ghadhban, Ahmed (M.S., Mechanical Engineering Program ) An Analysis and Simulation of Solar Water Desalination Systems Thesis dire cted by Professor Peter Jenkins ABSTRACT This dissertation presents theoretical analysis and simulations used to improve the performance of desalination systems and compares several solar desalination processes. This research demonstrate s how to use modular approaches for the dynamic simulation and steady state analysis of desalination by using MATLAB r2016a Simulink D ata from NIST (National Institute of Standard and Technology) and from SAM Advisor (System Advisor Model) were used in this study. Th ree types of distilled wa ter (pipe water, heavy water, and seawater) were used to compare the distilled fresh water produced from each solar desalination system. The potable water production rate from heating the feed water was calculated using empirical a nd theoretical modeling. Results of the modeling and experimental results were compared for both processes The simulations, modeling, and optimization of desalination processes using computer design technology are discussed. The results from this researc h could be used to predict the operating co nditions of desalination systems. The form and content of this abstract are approved. I recommend its publication. Approved: Pete r Jenkins

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iv ACKNOWLEDGMENTS I would like to thank my advisor, Professor Jenkins, for giving me the chance to work on this project. I am thankful for his help and patience. I also would like to thank my committee members: Dr. Premnath and Dr. Darbeheshti Each one of them has provided me with opportunities to advance my study and provided encouragement along the way. Also, I appreciate the people who have supported me, especially my family, my parents, my wife and my friends. Moreover, I would like to thank the Department of Mechanical Engineering for allowing me to utilize the library and labs to complete my research. I greatly appreciate the Mechanical Department workshop for the construction of the PV Solar desalination system. Finally, I am grateful to everyone who has encouraged me to pursue my project.

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v TABLE OF CONTENTS CHAPTER I INTRODUCTION ................................ ................................ ........................ 1 1.1 Background ................................ ................................ ........................... 1 1.2 Water Crises ................................ ................................ .......................... 1 1.3 Research Motivation ................................ ................................ ............. 2 1.4 Research Objectives ................................ ................................ .............. 2 1.4.1 Neural Networks for Modeling ................................ ........................ 3 1.4.2 Steady State and Dynamic Simulations ................................ ........... 3 1.4.3 Comparing Results ................................ ................................ .......... 3 1.5 Research Methods ................................ ................................ ................. 4 II PROPERTIES OF WATER ................................ ................................ ......... 5 2.1 Produced Water ................................ ................................ ..................... 5 2.2 Feed Water ................................ ................................ ............................ 6 2.2.1 Brackish Water ................................ ................................ ................ 6 2.2.2 Seawater ................................ ................................ ........................... 7 III DESALINATION ................................ ................................ ..................... 10 3.1 Desalination Use. ................................ ................................ ................ 10 3.2 Desalination Background ................................ ................................ .... 12 3.3 Desalination Process Classifications ................................ ................... 13

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vi 3.3.1 Membrane Process ................................ ................................ ......... 13 3.3.2 Thermal Process ................................ ................................ ............ 14 IV SOLAR ENERGY ................................ ................................ .................... 20 4.1 Introduction of Solar Energy ................................ ............................... 20 4.2 Sun Earth relationships ................................ ................................ ....... 20 4.3 Solar Radiation Definition ................................ ................................ .. 21 4.4 Solar Energy applications ................................ ................................ .... 22 ................................ ............................ 24 V PROJECT DESCRIBTION AND ANALYSIS ................................ ......... 27 5.1 PV Solar Powered Desalination ................................ ............................. 27 5.1.1 System Outline ................................ ................................ ................ 28 5.1.2 Develop PV Solar Array and Batteries ................................ ............ 31 5.1.3 Size Heating Source ................................ ................................ ......... 38 5.1.4 Provide Heat to the Water ................................ ............................... 41 5.1.5 Condensing the Vapor. ................................ ................................ .... 50 5.2 Solar Still ................................ ................................ ................................ 53 5.2.1 Solar Still Elements ................................ ................................ ......... 53 5.2.2 Energy Balance ................................ ................................ ................ 54 5.2.2.1 External Heat Transfer ................................ ....................... 55 5.2.2.2 Internal Heat Transfer ................................ ........................ 59

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vii VI RESULT ................................ ................................ ................................ ... 63 6.1 PV Solar Powered Desalination Results ................................ .............. 63 6.2 Solar Still Results ................................ ................................ ................... 78 6.3 Comparing the results ................................ ................................ ............. 81 VII DISCUSSION AND CONCLUSION ................................ ..................... 84 7.1 Discussion ................................ ................................ .............................. 84 7.2 Conclusion ................................ ................................ .............................. 85 7.3 Future Direction ................................ ................................ ..................... 85 REFERENCES 86

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viii LIST OF TABLES TABLE 1 Drinkable water standard of water ................................ ................................ ............ 5 2. Water saline category ................................ ................................ ................................ 7 3 Major ion concentration in seawater ................................ ................................ ........ 9 4. PV solar electrical characteristics ................................ ................................ .......... 36 5. Thermophysical properties of air ................................ ................................ ............ 41 6. Feed water types yield ................................ ................................ ............................ 76

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ix LIST OF FIGURES FIGURE 2.1 Ions concentration in seawater ................................ ................................ ...................... 8 3.1 Chart shows a fraction of the worldwide capacity of the desalination plants by regions. ................................ ................................ ................................ ................................ .... 11 3 .2 Installed desalina a nd w orldwide from 1950 to 2006 12 3.3 Thermal desalination process diagram ................................ ................................ ........ 14 3.4 Schematic diagram of multi stage flash ................................ ................................ ...... 15 3.5 Schematic diagram of multiple effect distillation ................................ ...................... 16 3.6 Schematic diagram of vapor compression distillation ................................ ................ 17 3.7 Global distribution of installed water desalination capacity by the technolog .. ......... 18 4.1 Sun Earth r elationships ................................ ................................ ............................... 21 4 .2 Variation of the solar radiation with the year ................................ ............................. 22 4.3 Available solar energy in the United States ................................ ................................ 24 4 .4 Photovoltaic cell panel. ................................ ................................ ............................... 26 5.1 PV solar desalination system. ................................ ................................ ..................... 27 5.2 PV solar powered desalination schematic ................................ ................................ ... 30 5.3 PV Module and batteries modeling in MATLAB/ Simulink ................................ ...... 31 5.4 Ideal PV c ircuit ................................ ................................ ................................ ........... 32 5.5 Equivalent circuit for PV m odule ................................ ................................ ............... 33 5.6 Typical P_V a nd I_V curve for PV m odule ................................ ................................ 36 5.7 Heating source sizing in MATLAB/Simulink ................................ ............................ 39 5.8 Schematic of water evaporative in MATLAB/Simulink ................................ ............ 45

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x 5.9 Two Phase fluid properties block 5.10 Water properties data (picture is taken from MATLAB). ................................ ........ 46 5.11 Rigid pipe block 5.12 H eat balance for condensate ................................ ................................ ..................... 51 5.13 Schematic of water condensate in MATLAB/Simulink. ................................ .......... 52 5.14 Solar still basin ................................ ................................ ................................ .......... 54 5.15 Overall energy balance ................................ ................................ ............................. 55 5.16 Schematic of solar still desalination ................................ ................................ ......... 62 6.1 P V curve characteristic ................................ ................................ .............................. 63 6.2 I V curve characteristic ................................ ................................ .............................. 64 6.3 PV Array characteristics for P V and I V c urves ................................ ....................... 65 6.4 Photovoltaic panel characteristics for different irradiance value s (1000, 500, and 100) 66 6.5 Actual power output in June in Denver for one PV p anel. ................................ ......... 67 6.6 Actual powe r output in June in Denver for t hree PV Panels ................................ ...... 67 6.7 Water distilled flow rate for piped water. ................................ ................................ ... 68 6.8 Vapor Water distilled temperature for piped water. ................................ ................... 69 6.9 Piped Water vapor fraction ................................ ................................ ........................ 70 6.10 Piped Water distilled production in one hour. ................................ .......................... 70 6.11 Piped Water distilled curve ................................ ................................ ...................... 71 6.12 Heavy Water distilled flow rate. ................................ ................................ ............... 71 6.13 Vapor and water distilled temperature for heavy water. ................................ ........... 72 6.14 Heavy Water production in one hour. ................................ ................................ ....... 72 6.15 Heavy Water distilled curve. ................................ ................................ ..................... 73

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xi 6.16 Heavy Water vapor fraction ................................ ................................ ..................... 73 6.17 Seawater d istilled flow rate. ................................ ................................ ...................... 74 6.18 Seawater distilled production in one hour ................................ ............................... 75 6.19 Comparing modeling r esults of water distilled from three water types ................... 76 6.20 Distilled Seaw ater production done experimentally in one hour. ............................. 77 6.21 Comparing fresh water productivity for Sea water from exper iment and modeling of PV solar m ethod. ................................ ................................ ................................ .............. 78 6.22 Solar Still modeling yield. ................................ ................................ ........................ 79 6.23 Water temperature and glass temperature ................................ ................................ 80 6.24 Reference e xperimental Solar Stil l distilled water ................................ .................... 81 6.25 Comparing the freshwater results from the PV Solar modeling approach with th e freshwater from Solar Stills m odeling for Seawater. ................................ ................. 82 6.26 Comparing the freshwater results from the PV Solar experimental approach with th e freshwater from Solar Stills e xperimental for Seawater. ................................ ........... 83

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1 CHAPTER I INTRODUCTION 1.1 Background The growing world population is rapidly increasing the demand for fresh water Only a bout 2.5% of water that exists on earth is fresh water [27], and this water is not distributed equally. G roundwater constitutes 30% of the fresh water resources [4] but i n arid and semi arid areas underground water is difficult to obtain and expensive to shi p Therefore, it s necessary to develop alternative s to produce potable water from salt water. Fresh water is required for industrial, agricultural, and domestic uses. C lean water shortages are a major factor in economic development. The oceans provide 96.5 % but the salt concentration renders this water not suitable for human use. S a lt concentration in oceans ranges from 33 37 ppt [7]. Seawater desalination is consider ed the best option to meet the demands of fresh water globally Desalination ha s already been successfully implemented i n several countries: Europe, southern and w estern parts of the US, and North Africa 1.2 Water Crises Many countries l ack natural sources of drinkable water and consequently, 1 billion humans cannot access clean water [35]. The potable water shortage has the world attention because water is necessary for the economic development and health to maintain the ecosystems [12]. Continued efforts are made to develop method s to get fresh water from d ifferent sources to provide water to people, farmers, and factories. However, fresh water sources are limited and retaining a balance in social and economic development result s in an imbalance between water supply and demand putting pressure on many coun resources The situation is further complicated because of the increasing rate of water

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2 consumption, due to population growth and the social and economic development Therefore, increase the global availability of water sources In response to this water crisis the desalination of seawater has become a main resource of water for the long term, and has already been implemented in several countries Among desalination processes, solar desalination is much more practical than oth er processes especially in arid areas where many water resources are available but suffer from a lack of a power supply. In spite of its high cost, solar desalination has a n advantage that satisf ies a variety of demands, and it is a clean source of energy Because of the potential to produce fresh water and support life on earth, developing desalination processes is very important. S olar desalination, in particular, requires immediate and significant efforts to design improvement s and control s for establishing the cost s associated with producing this technology 1.3 Research Motivation The importance of desalinated water will only increase as the natural water sources are deplete d In order to solve the fresh water problem, new water resources s hould be discovered, and new techniques developed. Desalination is considered a satisfactory technique for purifying conventional water sources. In several countries, fossil fuel has been used to provide power to water desalination system s For small syst ems low cost, solar powered water desalination may be preferred 1.4 Research Objectives The following topics will be analyzed in this research project: a. Neural networks for the predictive modeling of water desalination. b. Dynamic and steady state simul ations of a flash desalination system.

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3 c. Compar ison of the results between different types of solar desalination processes. 1.4.1 Neural Networks for Modeling A pplying a rtificial intelligence to the design and operation of desalination system s will lead to better design s and enhance d operation of these systems This process is a good choice for neutral networks because of the complexity of the process. The behavior is nonlinear with some degrees of freedom and this nonlinearity is due to the physical prop erties of streams depend ing on the pressure, temperature, and salinity. The amount of mass flow and heat transfer also contribute to the nonlinear behavior of the models in the thermal process. The neural network provides a suitable prediction model for the desalination modeling. 1.4.2 Steady S tate and D ynamic S imulations The goa ls of simulation and modeling for the industrial process es are improved and optimized in this project Steady state models are developed that involve algebraic equations. The d ynamic mod els are primarily applicable to estimate the performance and opti mization of the system. The d ynamic models involve differential and algebraic equations dependent behavior. Dynamic models are appropriate for the transient behavior simulations though they could also be used to analyze the system behavior under dynamic conditions. The motivation of system for this system simulation was to determine any enhancement s to the system for increasing the production of di stilled water. 1.4.3 Compar ing R esults In this research, the water produc ed from the solar powered desalination system was determined by two method s : PV s olar powered system and a s olar still. The methods used were:

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4 1. Compar e the fresh water results from PV Solar modeling simulation to the results from modeling the s olar still 2. Compare the fresh water results from PV solar experimental approach to the results from the experimental solar still 1.5 Research Methods T his research will use tw o different methods for the production of the distilled water. The first method was the photovoltaic solar powered desalination system. C omputer software program was used to estimate the production for three types of water systems based on the NIST (National Institute and Standards Technology) fluid properties. MATLAB Simulink was used to simulate the desalination process es and the SAM software was used to obtain the radiation properties The second method was the s olar still which was simula ted by using MATLAB r2016a.

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5 CHAPTER II PROPERTIES OF WATER 2.1 Produced Water Chemical substances may be found in drinking water supplie d from pipe water, but they are not dangerous to humans The following table presents a list of chemical substances in drinkable water, and the approximate safe levels (the levels more than the value in the table may cause a serious trouble) [9]. Table 1 D rinkable water standard of water Substance Nature of T rouble Level (mg/l) Chloride Taste and corrosion in hot water systems 200 600 Nitrate Methaemoglobinaemia for infants 50 100 Copper Taste discoloration and corrosion of pipes, and utensils 0.05 3 Iron Taste and growth of iron bacteria 0.1 Manganese Taste discoloration, and turbidity. 0.05 Phenolic compounds Taste, particularly in chlorinated water Less than 0.001 Zinc Astringent taste and sand like deposits 5 Magnesium Hardness taste 30 150 (or up to 250 if sulfate exists) Sulfate Irritation when combined with magnesium or sodium 250 Hydrogen Sulfide Taste 0.05

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6 2.2 Feed Water Feed water compositions are important for several reasons : a. They are necessary for the production of physical properties data used for design. b. To operation the system without scale formation, the compositions of scale constituting ions are important Seawater may have three times the salinity of brackish water, yet the some ion s concent ration in brackish water may be higher than seawater and produce more scale. c. In general, desalination processes such as reverse osmosis and electrodialysis are dependent on salinity and as a result, t he membrane process is used with brackish water more than with seawater. 2.2.1 Brackish W ater Brackish water is water that has a higher saline concentration than fresh water but less than seawater Brackish water may form from the mixing of fresh water and seawater in bodies such as estuaries [34]. Gen erally, the make up of brackish water lies between fresh water and seawater. B rackish water could be used safely and used for an environmental advantage for crop irrigation in arid areas. Technically, the salt concentration of slightly brackish water to brackish is between 500 2000 ppm, and it is only cautiously used for irrigation There are some classifications of salty water based on the salt c oncentration in water. Table 2 shows some of the salt water classifications based on salt concentrations [17].

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7 Table 2 W ater saline category Designation Total dissolved salts (ppm) Category Fresh water <500 Using for d rinking and irrigation. Slightly brackish 500 1000 Irrigation. Brackish 1000 2000 Using for i rrigation with caution. Moderately saline 2000 5000 Primary drainage Saline 5000 10000 Secondary drainage and saline groundwater. Highly saline 1000 35000 Very saline groundwater source Brine >35000 Seawater 2.2.2 Seawater P recipitation contains CO2 dissolved from air, whose carbonic acid causes the rainfall to be slightly acidic because of the carbonic acid that was formed from CO2 As rainwater erodes rocks, acids in the rainfall break s down the rocks T his process generates ions that flow in to rivers streams and ocea ns. The most dominant ions in seawater are chlorin e and sodium. Together, they form a less than 90 % of the dissolved ions in oceans [21]. The salinity (concentration of salt in seawater) is about 35 ppt (part per thousand) [8], [13]. In most marine areas, salinity is measure d as a total of all the salts dissolved in the water. 35 ppt is not a highly concentrated ratio, but the water in the o ceans or seas which have 35 ppt is very salty. The interesting characteristic of salt concentrated in water is that the dissolved salts are made up of the same type of minerals and salts, and they always appear in the same concentrat ion ratio to each other (even if the salt concentrat ion is different

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8 from the average concentrat ion )[8] The majority of sa lt in seawater is sodium and chlorin e, but other salts exist as well. Figure 2.1 I ons c oncentration in s eawater Figure 2.1 shows the major ions in s eawater[8]. The m ajor ions are those components whose s eawater concentration is more than 1 ppm (part per million). The reason for using this definition of major ions is that salinity is reported to 1 ppm [33]. Therefore, the major

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9 ions are the ones which contribute to the salinity. According to the definition, there are eleven major ions in seawater. Table 3 indicate s those ions and their concentration s (from Pilson, 1998) Table 3 M ajor ion concentration in seawater. Ion Concentration (g/kg) Na 10.781 K 0.399 Mg 1.284 Ca 0.4119 Sr 0.00794 Cl 19.353 SO4 2.712 HCO3 0.126 Br 0.0673 B(OH)3 0.0257 F 0.0013 Totals 35.169

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10 CHAPTER III DESALINATION 3.1 Desalination Use. D esalination specifically refers to the remov al of minerals and c ontaminated substances from salt water. Water sources can include seawater, brackish, rivers and streams, process water and industrial feed, and wastewater. Because of the saline this water is not appropriate for human usage, and it should be desalinated to use safely Desalination is already being used interna tionally for the following reasons : 1. Fresh water scarcity and natural sources can not fulfill the growing request for low salinity water. 2. The industrial requirement for pure water, such as for petroleum processing and power plants. 3. There is a deterioration of the quality of potable water resources. The rapid decreas e of underground aquifers and increas e of the salinity concentration in those non renewable resources exacerbate s the global water deficiency problem. 4. As technologies develop, water desalination becomes easier, and there are many types of desalination processes The d esalination process has improved rapidly, and it is used by several regions. It is already a satisfactory solution to water scarcity in the world, and it is now approved as a trustworthy resource for fresh water. According to IDA (International Desalination Association) the number of desalination plants operated in the world in 2015 wa s 18,426 These plants provided more

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11 than 22.9 billion US gallons daily, and s upplied fresh water for about 300 million people in 150 countries [1]. At present, about 1% of people in the world are depending on desalinated water to for daily requirements, but according to United Nations, 14% of the people in the world will be suffer ing from water scarcity by 2025 [2]. Figure (3 1), shows desalination distributions in the world basing to the regions [19]. Figure 3. 1 C hart shows a fraction of the worldwide capacity of the desalination plants by regions

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12 3.2 Desalination Background Desalination is a natural phenomenon that has already been occurring on the earth for billions of years. The natural water cycle ( water evaporat ing from the sea and then condens ing to form pure rainfall ) is the clearest example of the water desalination pr ocess Creek sailors heat ed water to evaporate fresh water from the saline water. In 1804, the first public water plant built in Scotland by Robert Thom was based on slow sand filtration [5]. Since 1960, the worldwide capacity for desalinated water has grown exponentially [3]. The following figure shows the worldwide desalinated water capacity since 1960 Figure 3. 2 I nstalled desa USA and worldwide from 1950 to 2006 [3].

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13 3.3 Desalination Process Classifications Desalination is an energy intensive system and involves expensive infrastructures. Thus, several desalination methods have been industrialized over the years to yield potable water from saline water economically. Desalination processes can be classified based on the separating system that is appl ied into physical, thermal, and chemical processes. There are two major types of de salination methods: membrane and thermal. 3.3.1 Membrane Process The m embrane separation process includes the passage of water into a semipermeable film under a pressure P ressurization reverses the natural transport of water that occurs from a dilute side to a more concentrated The m embrane process needs driving forces such as electrical potential, vapor and pressure to overcom e the n atural osmotic pressures and effectively force water through membrane processes The m embrane pr ocess is subdivided into two types [26]: a. Reverse Osmosis (RO) b. Electrodialysis (ED) Reverse Osmosis is a pressure driven process. The operating pressure range of RO is from 3.4 68 bar [10] RO was commercially presented in the 1970s and currently, RO is the largest desalination process method used in the USA. RO is used for desalinating feed water with a salt concentration more than 15,000 ppm [26]. Electrodialysis is a direct current driven process. Electrical power is used to transfer the rane and then separate them to create potable water as a product. ED was commercialized in the 1960s [26]. ED was initially considered a seawater desalination method, but it has largely been used for desalinating salt y or brackish water

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14 Because of the essential features of the electrical methods used in Electrodialysis sy stems ED is typically used to treat brackish water rather than seawater. 3.3.2 Thermal Process T he thermal process technology, as the term indicates, involves heating saline water to its boiling temperature to produce vapor, and then condensing the vap or to obtain fresh water. The thermal process is one of the oldest and most common technique s used Thermal technologies are used with seawater, but have seldom been used with brackish water due to high costs. In the thermal process thermal energy could be obtained from conventional hydrocarbon sources or nonconventional solar energy sources. Therefore, the thermal process involves a source of ener gy to give the system enoug h power for operation The source could be a fossil fuel source, or a renewable energy source such as solar power Figure 3 3 T hermal desalination process diagram

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15 I. Conventional Hydrocarbon Sources The thermal process us es fossil fuel s to heat saline water and form a vapor. There are many types of desalination processes which use the conventional energy such as [26] : a. Multi Stage Flash Distillation (MSF). b. Multiple Effect Distillation (MED). c. Vapor Compression Distillation (VCD). Multi Stage Flash Distillation MSF is one of the thermal desalination types which has been in use since about the 1950s. MSF facilities involve a number of chambers connected together MSF is the process which has a stream that flows through a bottom of stages (chambers), with each successive stage operating at a s equentially lower pressure [26]. A proportion of the s tream of brine flashes into vapor and will be condensed and collect ed as fresh water. In MSF distillation, feed water is heated in sequence d stages. A MSF plant could c ontain from 4 to 40 stages [24], [36]. Figure 3.4 Schematic Diagram of Multi Stage Flash [36]. Figure 3 4 Schematic diagram of multi stage flash [36].

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16 Multiple Effect Distillation The MED is a thermal process method which has been used over 100 years, making it the oldest desalination technique which is still used. The MED desalination technique occurs in series of effects (vessels) and it reduces the pressure in successive steps In a typical plant, there are from 8 to 16 steps [24]. The Multiple Effect distillation is similar to Multi Stage Flash distillation, which uses an evaporative technique that occurs in a series of effects o r chambers. However, the MED differs from the MSF in wh ich the steam formed in one step condenses in the next one. Also, in a multi effect distillation, feed water could be sprayed onto a tube bundle or flow onto vertical surfaces to promote a fast boiling and evaporation. Vapor which is generated in the fir st step, heat s up the second step for evaporation and is condensed in the tubes. These evaporation and condens ation process es occur continuously for several steps Figure 3 5 Schematic diagram of multiple effect distillation.

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17 Vapor Compression Distillation The VCD has been used for medium and small scale units, and it is based on the principles of decreasing the boiling point temperature by reducing the pressure. The heat used to evaporate the feed water comes from compress ing the vapor. Steam jets and mechanical compression systems are commonly used to condense steam to produce enough energy t o evaporate the incoming feed water Vapor compression di stillation has a comparatively high thermal performance and could be applied in the desalination of highly concentrated salt water. VCD is typically used in medium and small capacity applications. The following diagram provides a simple illustration of the vapor compression desalination system. The VCD is used in combination with an other thermal distillation process [24], [11], [36] Figure 3 6 Schematic diagram of vapor compression distillation [36].

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18 The following figure shows the global desalination capacity distribution according to the technology that is used II. Nonconventional Solar Sources. Sola r desalination or solar distillation is one of the available methods that is currently satisfying global water needs in several regions. Solar desalination is a suitable solution for small communities where sources of electricity are not available, and there is a plenty of solar radiation Furthermore, solar energy is consider ed a clean sour ce of power, and it is an environmentally friendly and a highly promising techno logy. Solar desalination has the advantage of cost saving s due to the fact that solar energy is a limitless power source and is easily accessible. Figure 3.7 Global Distribution of Installed Water Desalination Capacity by Technology [37]. Figure 3 7 Global distribution of installed water desalination capacity by technology [37].

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19 Solar energy is an appropriat e energy source for water desalination and is currently a popular area of research. T solar powered water desalination to be considered in the techniques for salt water desalination. Solar energy is one of a number forms of ther mal energy that could be used for providing power for desalination processes. The P erformance of solar desalination systems depends upon the design and climate conditions. Several efforts have been made to improve and develop the performance of solar disti llation. Solar energy can be used for desalinating water in an indirect way where the power from a solar energy device system is supplied to a distilled unit or in a direct way through solar stills There are two processes for the solar powered desalination techniques: a. Using photovoltaic cells to get the enough energy to heat the feed water. b. Solar stills Using photovoltaic cells (PV) The PV system is a simple approach involv ing the use of PV solar cells to generate enough electricity to supply power to a heating source to heat the feed water. The PV solar desalination technique uses solar energy as an indirect energy source. Photovoltaic cells can convert solar energy to electric ity to heat feed water which can then be combined with storage batteries. Solar Stills The solar still is one of the solar desalination methods that is used for distilled water from salt water. Solar still s use direct s un radiation to evaporate feed wate r, and can be used with a large or small system. A s olar still may be design ed to meet the water needs of a single family, and it is relatively inexpensive system s especially when use d for small groups.

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20 CHAPTER IV SOLAR ENERGY 4.1 Introduction of Solar Energy Solar radiation is a term for electromagnetic radiation, which is received from the sun. Solar radiation can be converted to useful energy such as electricity or heat. The Total Solar Irradiance (TSI) depends only on the distance between the sun and the earth and the total sun energy per second (time) [29] Not all of the sun radiation are absorbed by the earth : 29% of the energy is reflected, and the other 71% is absorbed by the oceans, lan d, buildings, and atmosphere [42 ]. 4.2 Sun Earth relationships The s un is a sphere of hot gasses, and its temperature is 5777 K. The mean distance between the earth and the sun is 1.495 10 11 m [29] The radiation emitted from the sun to the earth is a nearly constant amount, and it is called the sola r constant ( G ) [29]. The solar constant is the energy which is emitted from the sun per a time unit that is receive on the unit area of a surface perpendicular to a direction of the spread of the radiation at the mean earth sun distance. The absorbed radi ation contains visible light and infrared radiation. According to the World Radiation Center (WRC), the value of the Solar Constant (G) is 1367 w/m 2 [29]. The following figure shows the solar constant, and the average distance between the sun and the earth. As well as, the figure 4.1 shows the angle of solar radiation on the earth.

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21 Figure 4 1 Sun Earth r elationships [29]. 4.3 Solar Radiation Definition For engineering purposes, i t is important to understand the differences between types of solar radiation such as beam r adiation, diffuse radiation, to tal solar radiation, and irradiance [ 29]. Beam r adiation is received directly from the sun without have been changed by scattering over is also referred to a s direct radiation. T o avoid confusion between the direct solar radiation and d iffuse r adiation, the term of b eam r adiation is used [29]. Diffuse r adiation is the radiation that is received from the sun after it is scattered by diffuse radiation refers to sky radiation [29]

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22 Total s olar r adiation is a sum of the solar diffuse radiation and the solar beam radiation on a horizontal surface. Total s olar r adiation is also known as global radiation [29] Irradiance is the rate at which the radiant energy is incident on a unit area of a surface The Solar radiation which is received from the sun to the earth is a variety with a time of the year. The foll owing figure appears the variation of the extraterrestrial solar radiation with time. For engineering purposes, the energy that is received from the sun could be considered constant [29]. 4.4 Solar Energy A pplications Solar energy or solar power is a form of energy harnessed from the heat and power of (e co friendly ) energy source j ust like wind pow er These green energies are virtually inexhaustible unlike expendable fossil fuels Figure 4. 2 Variation of the solar radiation with the year [29].

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23 However, solar power is reliant upon the weather and the sunshine present in a location. Areas which lack sunlight or experience cloudy weather may have difficult ies us i ng solar power effectively Fortunately, most areas that suffer from water scarcity are located in regions that have an abundance of sunshine. Every hour, the sun emits enough power to deliver enough energy for a whole year across the globe [45]. Solar energy is used to create large amounts of power on a utility scale and to provide individual businesses and residences with electricity. Because sunlight is available almost everywhere, and it doe s not require fuel or connection to a power grid, solar ene rgy is useful for providing power to remote regions and for various portable devices. photovoltaic (PV) panels. The PV panels operate as conductors that take erat e energy (and electricity). Since technologies are developing and the ingredients of the materials used in the photovoltaic panels are becoming greener, the PV technique is becoming more accessible Most solar panels that are used today have an averag e life expectancy of 20 40 years [45]. However, s olar power generation is not a new technology; it has been used for more than 50 years. Most of solar energy use is on a small scale, and m ost of the large scale generation was developed in the 1970s and 1980s [32]. There are many applications for us ing the solar energy: 1. Heating residential buildings. 2. Electric power generation

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24 3. Water heating uses. Some areas in the United States are more apt for solar power than others. In 2009, California had the most solar power capacity, followed by New Jersey Almost all states in the U SA receive sunlight per squ are mile more than German [32]. 4.4.1 Solar rays are distinguished according to their wavelength s Infrared rays constitute around 50 % of light, while the visible light accounts for 40 %. T he remaining rays are ultraviolet which make up about 1 0 % Because most of the infrared rays are short waves, they are not considered warm radiation rays. The wavelength of infrared rays is less than 3000 nanometers [38]. Figure 4 3 Available solar energy in the United States [32].

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25 Using sunlight in buildings has the potential to significantly de crease energy consumption. This area of development is called day lighting, and it is one of the methods used to decrease energy consumption in buildings. Solar energy is easily converted into heat through absorption by liquid, gaseous or solid materials. Heat can then be used in sanitary water heating, water evaporati on and other purposes. Heat can also easily be converted into electricity and it could run or facilitate physical or chemical transformations. Solar radiation could also be observed as a flux of photons or electromagnetic particles. Photons that come from the sun are highly energetic, and they could promote photoreactions such as generating electron enabling the transformation of sunlight into electr icity. Note that the two fundamental approaches to capture the photoreaction and heat could also be combined in a number of methods to provide combined energy vectors e.g. electricity and heat Therefore, from the two basic methods (heat and photoreaction), we can distinguish some main domains of applications such as photovoltaic electricity and thermal power. Solar cells are made from semiconductor materials. When the sunlight is incident on the PV arrays, it knocks electrons in the PV ce throughout the cells, electricity is generated [32]. Modern PV solar cells were developed in the 40s and 50s from the last century, and the technology has improved over the past years The space programs of some countries such as the United States use photovoltaic solar cells as an energy source to generate power for spacecraft and satellites [32] PV panels have also been used for supplying electricity to remote areas that lack local electricity such as arid areas

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26 Solar cells are organized onto the solar panel. This solar panel is coated to protect the solar cells (usually coated on glass). Several panels are organized into an array that can be scaled to give enough energy. A single cell can pr oduce electricity to power an emergency telephone, though larger arrays are needed to power building s Figure 4. 4 Photovoltaic cell panel.

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27 CHAPTER V PROJECT DESCRIBTION AND ANALYSI S 5.1 PV Solar Powered Desalination PV Solar Desalination is a simple method which uses a Photovoltaic cell (PV) to generate electricity. The PVs supply enough power for the heating source (heater) to deliver a required thermal ener gy to boil the feed water to generate vapor and then this vapor is condensed to produce fresh water. The sun radiation is collected by the PV solar cells for producing the electricity which is stored in batteries The purpose of using the batteries with this system is to store extra power for use at night or in cloudy days. Figure 5 1 PV solar desalination system.

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28 5.1.1 System Outline Compared with other desali nation systems, the PV Solar desalination has several differences Because prototyping testing is cost ly and time consuming it is difficult to predict the performance of the system. Therefore, modeling and simulation are important for concept evaluation, prototyping, and an alysis of PV solar desalination sy stems. Furthermor e, the modeling process could model not only the thermally simulated modules but also the embedded software which was used to control all the required components MATLAB/Simulink is a general purpose modeling and simulation package used in science and e ngineering design and research for the modeling of engineering systems. MATLAB, Simulink, and Simscape were used for modeling the desalination system Simscape enables the designer to build models of physical systems in the Simulink envir onment rapidly. Simscape could also be used to build component models based on a physical connection which directly integrates with other modeling diagrams Simscape provides a complex component and analysis capability It also help s to test the system and develop the The models can be parameterize d using MATLAB r2016a expressions and variables [6]. The inputs for run ning this project after completing the design depend on weather conditions and the amount of feed wa ter. The weather conditions include and the temperature of the day. T o design and test the solar desalination, the PV panel, heat system, and condensate system were modeled in MATLAB r2016a and the Simulink environment The model was

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29 developed using physical principles and empirical data. Emp hasis was given o n maintain simple component models The model was developed to determine the distilled water production from feed water by using Matlabr2016a Simulink/Simscape simulation. To faci litate the modeling process t he project was divided into four steps to simulate the process Develop PV Solar Array and Batteries. Size Heating Source (Heater). Provide Heat to the Water. Vapor Condensing. The following schematic represents the outline of the system that was design ed using MATLAB r2016 Simulink/Simscape. The design depends on the physical properties of water according to the National Institute of Standard and Technology (NIST) software whi ch i s related to MATLAB r2016a environment software. Each s were connected with each other by Simulink blocks obtained from the Simscape library which was especially useful for simulating thermal fluids. Some data of the comp onents t hat exist in the MATLAB library were used. T he process (modeling) was arranged with successive steps from the modeling of the photovoltaic system to the production of water. Simulink models were assembled as connected blocks which were structured hierarchically.

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30 Figure 5 2 PV solar powered desalination schematic

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31 5.1.2 Develop PV Solar Array and Batteries The PV Solar panel was the main component in the solar power system which generated electricity that was stored in batteries. The panels were integrated with charged batteries to give the system stability and continuity. As a result, the production of water wa s more consistent. Figure 5 3 PV module and batteries modeling in MATLAB/ Simulink

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32 The first step was to determine the Photovoltaic solar module data. 1. For an ideal PV Circuit, the following parameters are used in the model : [16], [18] ( 1 ) [16] ( 2 ) [16] ( 3 ) I is the PV output current. is the thermal voltage K is the 23 J/K. = 1.602 *10 19 coulomb. Figure 5 4 Ideal PV c ircuit

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33 is m odified ideality factor is the current generated by the incidence of light is the diode reverse bias saturation current. At a short circuit; and At an open circuit; I=0 [16] ( 4 ) 2. For an equivalent circuit with series and parallel resistances : The power output from the electrical circuit is expresses by the relation; [29] [29] ( 5 ) Figure 5 5 Equivalent circuit for PV m odule

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34 [29] ( 6 ) I L is the current generated by the incidence of light. I Sh is the shunt current. Rs is the series resistance Rsh is the shunt resistance I D is expressed in the same way of the equation (2) Thus the circuit needs five parameters to operate (I L I D Rs, Rsh, and a ) Modified ideality factor a is related to the known physical parameters (k, T, Ns and q) and the unknown parameter n by the equation [29]; ( 7 ) n is the ideality factor For an ideal diode, n=1. For real diode, n is between 1 and 2. The five parameters (I L I D were obtained by using the measured characteristics of the voltage and current of the module at the reference conditions that are supplied by a manufacturer. The power voltage measurement s were made at a cell temperature 25 o C, incident radiation 1000 W/m 2 and spectral air mass equal to 1.5 [29]. The current voltage measurements at the reference conditions were available from the manufacturer at maximum power, short circuit conditions, an d open circuit conditions. The manufacturer also supplied the temperature coefficient ( ) of short circuit current, and the temperature coefficient ( ) of open circuit voltage [29]

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35 [29] ( 8 ) is the PV cell temperature. is the PV cell reference temperature. is the effective absorbed solar ratio. [29]. The value of the diode current is given by [29]; ( 9 ) is a bandgap energy of a material w hich is ; E g / (E g,ref ) (T T c,ref ) [29] ( 10 ) For silicon; E g = 1.794 10 19 J. C= 0.0002677. The series resistance Rs does not depend on the temperature or the solar radiation; Rs=Rs,ref [29]. The shunt resistance Rsh depends on the absorbed solar radiation and does not depend on the temperature; R sh R ( sh,ref ) S ref [29] ( 11 ) Based on Rauschenbach (1980), the negative inverse of the shunt resistance was approximately equal to the slope of I V curve at the condition of open circuit voltage. [29] ( 12 ) a/a ref = T c /T c,ref [29] ( 13 ) The following table presents the PV module electrical characteristics that were obtained from the manufacturer.

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36 Table 4 PV solar electrical characteristics Maximum Power P max. 320 w V mp 54.7 V I mp 5.86 A V oc 64.8 V I sc 6.24 A Efficiency 19.6 % Total number of series cell Ns 96 PV Solar module data for Sunpower SPR E19 320. For this project the data which shows in T able 5.1 were used to design the PV Array, and it was chosen because of the high module efficiency which was more than 19 %. For estimating the PV solar panel daily operation, it was important to know the daily peak sunshine hour (PSSH) for the location where the PV Array wa s installed. Figure 5 6 Typical P_V and I_V curve for PV m odule [29].

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37 PSSH refers to the solar radiation which a particular location could receive if the sun is shining at its maximum rate for a certain number of hours. The average PSSH in Denver, Co. =5.5 hour/day for fixed tilted array at latitude [41]. The following parameters were used ; The required load energy for operating the desalination system per day is El. The PV array thermal factor is Fth Then, Equation (14) expresses the power that the PV array should generate for a desalination system that operates with El energy per day. For estimating should know the power that is generated from the PV array module which was used in the desalination system. ( 15 ) Because of the variations in the PV power resulting from the change in weather, the system could have operational problems. Thus the battery storage was necessary to stabilize the energy input to the system especially For sizing the batteries there were two parameters to be estimated: the battery capacity rating (AH) and the battery voltage. The maximum depth of discharge for battery is D OD [23]. Peak Power for PV Array (kW) [22] ( 14 )

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38 Battery Capacity ( kW h) = [23] ( 16 ) The output voltage which was required from the battery was Vr. T hus, T he battery capacity (AH) wa s given by; Battery Capacity (AH) = [23] ( 17 ) For the project, the output voltage which was required from the battery was 24 volt s Therefore, the battery capacity could be obtained with only a 24 volt battery or two of 12 volt batteries How ever, using four batteries with 6 volt battery was preferred since the 12 volt, and 24 volt batteries were heavy Using more than four batteries might cause an unbalance in the battery charging and discharging. 5.1.3 Size Heating Source The electric heater was designed as a cylinder around a pipe to generate a uniform heat at a specified temperature. The initial temperatur e was the ambient temperature, and a thermostat was designed to limit the By controlli ng the power input to the heater a uniform heat production of the heater the time. The following figure is a schematic diagram which illustrates the heater mo deling in MATLAB/Simulink.

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39 The Power comes from the PV Array and Batteries storage assembly. The final temperature was the temperature which was delivered to heat the feed water. This heating simulation was built using the following analysis which represent s the heat production by the coil heater with a uniform heat generation and a constant temperature. The cylinder heater has diameter D h and length L h in (m). The heat capacity (specific heat) is C p,h kg/m 3 The heater surface area, S, was for an open sided cylinder with a thin thickness ( th ) and given h *L h Thus; 3 ( 19 ) W here ; ( 18 ) Figure 5 7 Heating source sizing in MATLAB/Simulink

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40 m was The useful heat which was generated by the heater was Q h ( 20 ) ( 21 ) The power input s to the heater was P, and it was the same power that was delivere d by the batteries The total heat which was generated from the power P wa s Q. ( 22 ) to the ambient wa s Ls. Thus, ( 23 ) ( 24 ) Where; T h s temperature T i T a is the ambient temperature. h a is the heat convective coefficient of the ambient air. ( 25 ) Ka is the heat conductive coefficient of air. [20] ( 26 )

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41 Pr is Prandtl number, and Re is Reynolds number. [29] ( 27 ) kinematic viscosity. Thus, ( 28 ) Table 5 Thermophysical properties of air [20]. Temperature (k) Pr 100 2.00 9.34 0.786 150 4.426 13.8 0.758 200 7.59 18.1 0.737 250 11.44 22.3 0.720 300 15.89 26.3 0.707 350 20.92 30 0.7 400 26.41 33.8 0.69 Incropera, Frank P.; DeWi tt, David P. (2002) 5.1.4 Provide Heat to the Water Heat that transfers from the heater to the pipe by radiation, and it is expressed by Stefan Boltzmann law : [20] ( 29 ) Assume the shape factor was equal to one [14]. The was given by [20];

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42 ( 30 ) W here ; 8 is the Stefan Boltzmann constant. is the emissivity coefficient. D p is the feed w T p The heat that transfers into t he pipe to heat the feed water wa s transferred by conduction and convection. A. Th e energy conducted through the pipe wa [20] ( 31 ) ( 32 ) Assuming the heat transfer is in one dimension and steady state and has constant properties. Thus, : [20] ( 33 ) A ssuming the heat transfer s in (r ) dimension. K is the heat transfer conductive coefficient of the pipe For Quasi steady state without heat generat ion for cylindrical coordinates ; ( 34 ) By solving the above equation, we get;

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43 ( 35 ) Where; C1 and C2 are constants. Solving equation (35) at the boundary conditions, T(r) = T po at r o and T(r) = T pi at r i. After solving the values of constants (C1 and C2), the temperature distribution equation in the pipe is; ( 36 ) Thus, equation (33) will become ( 37 ) T po and T pi er wall temperature, and inside wall temperature. r o and r i outer r adius, and inner radius. L p B. The energy which is transferred by convection from the pipe to feed water is expressed ( 38 ) ( 39 ) is the temperature differen ce between the water before heating and after heating. K w h w convective coefficient area.

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44 D i For calculation Nusselt number Nu, Re mus t be determined as, ( 40 ) V w w kinematic viscosity. Water flux or water flow rate is equal to water velocity multiplying the area cross section. ( 41 ) From equation (41), the water velocity V w is obtained (water flow rate is known) Choosing the tube wetting ratio perimeter for the flow between 0.03 0.14 ( 42 ) w r is the wetting rate, which is the feed water flow rate per pipe unit length. For laminar flow with a constant surface temperature, the Nusselt number could be estimated as follow: For turbulent flow, for Re>2300 [20]. The required heat energy for evaporating the m mass of water is given by, ( 43 ) Q re is the required energy to evaporate the mass of water. T is the water temperature in the initial state. T b is the water boiling temperature C pw is the water specific heat j/ kg.C.

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45 L is the latent heat evaporation of water j/kg. is the water flow rate kg/s. The above figure presents the heating water assembly schematic which was simulated in MATALB/Simulink. The process was simulated in MATLAB/Simulink by using the water properties based on the NIST software. Figure 5.9 Two Phase fluid properties block The block above was used to determine fluid properties in the MATLAB/Simulink. It provides thermo physical properties of two phase fluid. This block parameterizes the properties of fluid in terms of a normalize internal energy and pressure. Figure 5 8 Schematic of water evaporative in MATLAB/Simulink

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46 (From MATLAB) is the normalize internal energy, is the fluid specific internal energy, is the fluid specific internal energy of the liquid phase at saturated, is the minimum internal energy of the fluid in the 2 phase state The following models the water flow inside the rigid pipe. Figure 5.11 Rigid pipe block The ports A and B represent the inlet and outlet of the pipe The port H represents the thermal port for the heat transfer between the pipe and the surroundings. The total thermal energy is equal to the sum of internal energy and kinetic energy. (From MATLAB) Figure 5 10 Water properties data (picture is taken from MATLAB).

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47 is the total energy of water, u1 is the water internal energy, is the total water mass in the pipe, is the water mass flow rate into the pipe through the port A and B (the above equation is from MATLAB ). For understand the evaporation state, it is im portant to understand the V apor Liquid Equilibrium concept The Vapor Liquid Equilibrium (VLE) condition is that the Gibbs energy is minimized at a known pressure and temperature. This means that the Gibbs energy is constant for any small perturbation [44] [44] ( 44 ) So, G gw = G lw G gw is the Gibbs energy in a vapor (gas) phase, G lw is the Gibbs energy in a liquid phase, and dn w is the small water amount. When the temperature increases, the water molecules in the liquid phase move more rapidly and it becomes more likely to convert into the gas (vapor) phase. Thus, the pressure of the vapor increases with temperature. The relation between vapor temperature a nd pressure is given by Clapeyron equation; ( 45 ) V= V g V l P sat is the saturated vapor pressure V g is the volume of the vapor phase. V l is the volume of the liquid phase

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48 In most cases, V g is greater than V l and for ideal gas (treated the vapor as an ideal gas) [44] So, the Clapeyron equation becomes; ( 46 ) R is the ideal gas constant. ( 47 ) Since 1/p dp= d lnp. E quation (47) is Clausius Clapeyron equation, which applies at low pressure s (less than 10 bar ). It is used to calculate the vapor pressure at a given temperature. A more practical equation that is used for computing the vapor pressure is the Antoine Equation; ( 48 ) A, B, and C are the Antoine parameters for fluid. Seawater is a mixture of water and several compositions ( more than 85% of the mixture is sodium and chloride as shown in Figure 2.1). For any seawate r component, the partial pressure of any component equals to the vapor pressure of the component multiplied by its mole fraction [44]. ( 49 ) ( 50 ) p and p i are the seawater pressure and component partial pressu re in the liquid phase.

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49 x i and y i are the mole fraction of the component in the liquid phase and the vapor phase in vapor liquid equilibrium Also ( 51 ) Equation (51) is T he variable K value equals to y i / x i Substitute K value d it. ( 52 ) The s um of the all vapor components mole fraction is equal to 1. ( 53 ) Also, ( 54 ) For ideal gas; ( 55 ) For any component, the feed water (F) fraction is z. The heated feed water has a vapor (V) fraction y and residual liquid (L) fraction x. ( 56 ) Substitute K value value in equation (56). ( 57 ) ( 58 ) Since L= F V, Then ;

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50 Since and Use the relation ( 60 ) The above expression is Rachford Rice equation. The boiling point of mixture fluid such as seawater is different from the boiling point of pure fluid such as water. Ther efore the boiling point elevation of seawater is given by the following equation ; T b is the boiling point elevation. T b is the normal wate r boiling point temperature. x b is the mole fraction of the compositions that exist in the sweater. L is the R is the ideal gas constant. 5.1.5 Condensing the Vapor. Condens ation is a process in which water vapor is converted to liquid when the temperature of the vapor falls below its saturation temperature. The condensation process occurs when vapor molecules come in contact with cooler molecules. The vapor will lose energy when the heat transfer of energy occurs and the vapor will convert to liquid. The energy balance of condensate the vapor is the same energy balance for evaporated the water but in the opposite direction. ( 59 ) ( 61 )

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51 Figure 5 12 Heat balance for condensate [20]. The energy that is released from condensation process is expressed by [20]: ( 62 ) q rel is the energy released. T 1 is the water condensed temperature. T 2 is the cooling temperature. ( 63 ) R total is the total heat transfer resistances. ( 64 ) r 1 and r 2 are the inner and outer pipe radius, h 1 and h 2 are the heat convective coefficient of water and air respectively ( 65 ) F or constant temperature equals and

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52 Nu= 3.66 [20]. ( 66 ) Nu is estimated in the same way in the equation (26). ( 67 ) Th is expressed by [44]; ( 68 ) Also, considering the following equation. ( 69 ) Figure 5 13 Schematic of water condensate in MATLAB/Simulink

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53 ( 70 ) Replace p i,sat (T) in the Antoine equation (equation (48)) : So, Antoine equation will become; ( 71 ) Substituting the above equation in to (equation (68)) to estimate the condensation temperature, and this condensation temperature is used to c alculate the saturated pressure p i,sat (T). Finally, the condensate mole fraction is given by, ( 72 ) 5.2 Solar Still The basic principles of solar still distillation ar e simple but effect ive, as t he sun's energy heats the feed water to the point of evaporation. As the water evaporates, this vapor rises and condens es s process eliminates impurities such as minerals, and removes microbiological organisms. The re sult is fresh water. Thus, the solar stills desalination process uses wa ter and then condenses it. T he clean water is collected as drinkable water. Modeling was used to predict the operation of the thermal system design for the solar still desalination process. 5.2.1 Solar Still Elements The essential elements of Solar Still are : 1) F eed water basin. 2) Incoming radiation.

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54 3) A transparent cover (glass or plastic). 4) Collection pipes that collect the condensate water. 5) Other miscellaneous parts such as sensors s the water in the basin and evaporates the water. The water then condenses under the transparent cover as droplets. These droplets flow down into the collecting pipes Figure 5. 14 Solar still basin 5.2.2 Energy Balance To model the energy balance of the solar still, the following process was followed. The sunlight passes through the cover of the still and is absorbed in the seawater layer and by the black cover in the basin, heating the basin and seawater. Also, the seawat er is he ated by

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55 the black surface by conduction heat transfer. As a result the seawater temperature increases. Vaporization will take place on the surface of the seawater. The seawater surface is semi permeable which that means the mass flux of one compon ent is zero. For e xample, the water that evaporates from the surface evaporat es into an adjoining air stream. Therefore, the saturated air at the interface is transported by diffusion because of the partial pressure difference s and by convection because of the natural convection of the air from the feed water interface into the air inside the basin. Based on a quasi steady state energy balance the air inside the basin is also saturated. Thus, the saturated air inside the basin will condense at the cover 5 .2.2.1 External Heat Transfer The external energy balance on the solar still includes the cover and the basin bottom losses. A ssume there is no temperature gradient along the cover ( 73 ) I w R w g R g b are the solar radiation intensity, water absorptivity and reflectivity, the glass cover absorptivity and reflectivity, and basin bottom absorptivity. Figure 5. 15 Overall energy balance

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56 ( 74 ) ( 75 ) ( 76 ) Where; C pw is water specific heat capacity. is the distilled water mass. q b is the basin heat transfer, q cb is the basin bottom heat losses, and q s is the heat losses from the side. The heat losses from the solar still occur on the c over, the bottom, and sides to the ambient by convection, radiation, and conduction. The heat losses from the solar still that occur on the c over, the bottom, and sides to the ambient are by convection, radiation, and conduction. I. Losses from the cover : by convection and radiation. Convection heat transfer losses from th e cover to the ambient is given by, ( 77 ) T a is the ambient temperature. T g is the glass cover temperature. h cg is the glass cover heat transfer convective coefficient. Radiation heat losses are given by [39 ], ( 78 ) h rg is the heat transfer radiative coefficient.

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57 ( 79 ) T sky is the sky temperature which is given by [28] ( 80 ) emissivity Boltzmann constant. The overall glass heat transfer by radiating and convection is q g [39] ( 81 ) ( 82 ) And; [39] ( 83 ) W here ; h tg is the total heat transfer losses coefficient from ambient to glass It expressed according to J. H. Watmuff, 1977 ( 84 ) II. Losses from the bottom and sides: Losses from the bottom and sides are by radiation, conduction, and convection. ( 85 ) ( 86 ) q bs is the total losses from bottom and sides. T b and T a are the temperature of the basin and ambient respectively. U o is the basin overall heat loss coefficient. ( 87 )

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58 W here ; U b and U e are the heat loss coefficient of bottom and sides respectively. ( 88 ) ( 8 9 ) Where; L ins and K ins s insulation thickness and thermal conductive coefficient h cb and h rb are th e basin heat transfer convective and radiative coefficient. On the bottom, there is no wind speed, th us, h cb +h rb =h tb and it estimate d such as equation (84) with wind speed is zero. Therefore, h cb +h r b = 2.8 w/m 2 h w is the water heat tran sfer convective coefficient. The Nusselt number inside the still between the water and glass cover is given by Dunkle [30], [43 ], ( 90 ) C and n depend on the Gr. C=0.21, n= 1/4 for C=0.075, n=1/3 for Gr is Grashof number and is expressed by, ( 91 ) B, g, L b coefficient of expansion, gravitational constant, space between the glass cover and water, and the kinematic vis cosity respectively.

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59 [20 ] is the thermal diffusivity. ( 92 ) A b and A s are the basin bottom area and the basin side area. With A s A b the U e was ignore d [39]. 5.2.2.2 Internal Heat Transfer I nternal e nergy b alance means that the heat transfer occurs inside the solar still between the f eed water surface and the cover by radiation, convection, and evaporation [39]. Figure 5.14 shows the model of the distilled water in a typical solar still I. Irradiative heat transfer The rate of heat radiation from the water surface to the cover is, ( 93 ) h rw is the irradiative heat coefficient and it is given by [39] ( 94 ) The effective emissivity is given by ( 95 ) w g are the wate r and the glass cover emissivity II. Convective heat transfer The general convec tive heat transfer equation is given by, ( 96 )

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60 h cw is the heat convective coefficient betwe en the basin bottom and amb ient and it is given by [30 ]. ( 97 ) W here is the partial pressure at the water surface is the partial pressure at the glass cover. ( 98 ) ( 99 ) III. Evaporative heat transfer The general evaporative heat transfer equation is given by ( 100 ) [39] ( 101 ) The hourly yield is given by [18 ] ; ( 102 ) Where; m is the hourly distilled water from the solar still. L is the latent heat vaporization. The overall heat coefficient loss between the glass cover and water surface given by; ( 103 )

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61 Solar still overall loss (U) is given by following equations [39] ; ( 104 ) U t the top overall losses. ( 105 ) ( 106 ) Thus, ( 107 ) The water t emperature T w is given by [39]; ( 108 ) Where, f is a function, and it is given by; ( 109 ) The value of eff is obtained from the following equation. ( 110 ) Where; a a is constant and equal to U/(m w C pw ). T wo is the initial basin water temperature at time t=0 The glass temperature is assumed to have no gradient and expressed by [39]; ( 111 ) Where;

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62 T w is the water temperature. T g is the glass cover temperature. For the theoretical calculation, assume there is no temperature gradient in the glass cover and water. The following figure r epresents the modeling of the solar still desalination system that was design ed using MATLAB r2016 Simulink. Figure 5 .16 Schematic of solar still desalination

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6 3 CHAPTER VI RESULT In this section it will show the simulated results which were developed by MATLABr2016a and compare the simulation with the experimental results of the project Also, a comparison is made between the several solar desalination processes. 6.1 PV Solar Powered Desalination Results The simulated results for the Photovoltaic Array were b ased on the information from Sunpowers Company for their SPR E19 320 module. The following figures show t he relation between the output power with the v oltage (P V Curve) and the Ampere Voltage relation (I V Curve ). Figure 6 1 P V curve characterist ic

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64 Figure 6.1 illustrates the relation between the power output from the PV Solar and Voltage. The maximum power output ( P max .) occurs at the voltage (V mp .) and Current (I mp ). For this module, P max =320.27 W at the V mp = 54.6. As seen in the following figure, Voltage (V mp .) occurs at a Current I mp =5.86. ( 112 ) Figure 6 2 I V curve characteristic.

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65 T he following figure shows the relationship among the P max I mp ., and V mp for a PV Array. The above figures are based on a 1000 irradiance However, the solar irradiance is not constant throughout the day. Figure 6.4 shows the PV Array characteristics for three irrad iance values 1000, 500, and 100 In this project the theoretical calculations used the maximum operating point characteristics for estimating t he output power. Figure 6 3 PV Array characteristics for P V and I V c urves

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66 The following figure shows the PV Solar output power for an average June day in Denver, Colorado USA The values for that day were obtained from the System Advisor Model (SAM) program. It is clear that the actual power output from the PV solar was not adequate to give the required estimated power of 320 W Thus, using more than one PV panel was needed to provide the required power. In this project, three PV panels were used. Figure 6 4 Photovoltaic panel characteristics for different irradiance values (1000, 500, and 100)

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67 Figure 6 5 Actual power output in June in Denver for one PV p anel. Figure 6 6 Actual power output in June in Denver for t hree PV p anels

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68 From figure 6.6, it is clear that the PVs Array does not provide enough power to operate the system from about 6 pm to 8 am Therefore, batteries were needed to keep the system work ing continuously. The batteries were charged from t he PV during the period from 8 am to 6 pm and discharged from 6 pm to 8 am to give the system the continuous required operating power. The distilled water obtained from the piped water, heavy water, and sea water are shown in the following figures. In the f igures for the distilled feed water production flow rate was for a sample of 6 minutes. The distilled water was measured in kg/s or (liter/s) and with time in seconds. Figure 6 7 Water distilled flow rate for Piped W ater. As shown in the above figure the production started after about 50 seconds. Initially, t he distilled water flow rate was high and then decreased over time. The reason for the initial

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69 high value was that the condensation pipe at the beginning of the ope ration was not warm and because of the vacuum pressure that occurred during the starting of the distillation process. Thus, this initial period was neglected in estimating the production of the water. Figure 6.8 shows the vapor and water temperature s i nside the heating and condensation pipes Figure 6 8 Vapor Water distilled temperature for Piped W ater In Figure 6.8, the difference in temperature between the vapor (red line) and the water distilled (blue line) at the beginning of production was the largest. Also, the difference in the temperature of the water and vapor through out the period when the unstable production occur red was zero. Therefore the vacuum pressure cause d the unstable production.

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70 The system stabilized after about 70 seconds and start ed to give stable distilled water. Figure 6.7 shows the uniform system flow rate measured in kg/s. The production of u niform water was the goal of using this system which was connected to batteries Fi gure 6 9 Piped W ater vapor f raction. Figure 6.9 shows the ratio of t he vapor after heating and condensation process The red line refers to the vapor ratio after the heating process while the blue line refers to the vapor ratio after condensation process Th e production for one hour is shown in the figure 6.10. Figure 6 10 Piped W ater distilled production in one hour

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71 The amount of production of u niform distilled water is shown in figure 6.11. The amount of water was about 1.843 liters per hour Figure 6 11 Piped W ater distilled curve For heavy water, the feed water was preheat ed Figure 6 12 Heavy W ater distilled flow rate.

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72 Figure 6 13 Vapor and water distilled temperature for heavy water As seen in the above figure the temperature of the water distilled was the same temperature of the vapo r which means the system was operating in the vapor liquid equilibrium (VLE) zone. The water distilled in one hour was about 1.773 liters. Figure 6 14 Heavy Water production in one hour The heavy water distilled c urve was also uniform and is shown in the following figure

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73 Figure 6 15 Heavy Water distilled curve Figure 6 16 Heavy water vapor fraction.

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74 The vapor fraction was uniform for the heavy w ater desalination. The seawater desalination behavior was similar to the previous water desalination types The distilled sea water flow rate was les s than the other, which resulted from its higher boiling temperature. T bb b +373.15. T bb b is the boiling point elevation (the difference between normal water boiling temperature and seawater boiling temperature) T b =0.5942 Thus, T bb = 3 73.74 Sea water distilled production flow rate wa s constant with the time. Figure 6 17 Seawater d istilled flow rate.

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75 From the above figure, it can be seen the time to start the desalination production was longer than for the piped and heavy water. The reason for this delay is that the seawater consists of more compositions than the piped and heavy water. The hourly production was 1.409 liters per hour. Figure 6 18 Seawater distilled production in one hour. The distilled water curves for piped water, heavy water, and seawater per hour are a linear relation, and the expression could be written mathematically as, Y= C (X t d ) Where; t d is the time when the distilled starts. C is a constant.

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76 Table 6 Feed water types y ield For piped water, the boundary condition at X= 3600 and Y=1.843 C= 1.843/(3600 50) = 0.00519. And for heavy water, the boundary condition at X=3600 and Y=1.773 C=1.773/(3600 64) = 0.00501 And for seawater, the boundary condition at X=3600 and Y=1.409 C = 1.409/(3600 107) = 0.00403. Figure 6 19 comparing modeling results of water distilled from three water types The experiment was done for seawater, and the result s are shown in the following figure Feed Water Desalination starts Time (s) Yield water per hour ( liter ) Piped water 50 1.843 Heavy water 64 1.773 Seawater 107 1.409

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77 Figure 6 20 Distilled Sea water production done experimentally in one hour. The experimental w a ter production had an approximate linear behavior. There was a difference between the theoretical solution of the distilled water production which was obtained from simulation of the MATLAB software and the experiment. This difference was because the sof tware simulation ha d the assumption that the weather conditions such as constant wind speed and temperature during one hour, while in actual testing there were differences in the weather conditions during one hour. The difference in wind speed was not tak en into account in the numerical estimation. The average wind speed was taken as 5 m/s. The distilled water from the experiment was about 1.19 liter per hour. The following figure shows the difference between the modeling and experimental distillation of seawater It shows a small differen ce in the linear relation for the production of

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78 water. B oth production curves might be more similar if the testing had been done indoor without the effects of wind. Figure 6 21 Comparing f resh water productivity for Sea water fr om experiment and modeling of PV solar method. 6.2 Solar Still Results The data used in theoretical calculation which was made by the MATLAB simulation were taken from 8 am to 5 pm The calculation does not estimate the data from 5 pm to 8 am since there was not enough solar energy available It was a ssumed that there was no temperature gradient throughout the cover due to a small thickness of the cover. The testing was done for sea w ater only.

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79 Figure 6 22 Solar Still modeling yield. From the above figure it can be seen that the distilled water increas ed with time until it reache d a peak value and then decreas ed. The reason for the increase was that the solar energy was increasing in the morning and that le d to an increase in the water production, while in the afternoon there was a decrease in producti on according to the change in solar energy. When the solar energy was increasing the energy absorbed by the system increased, which led more heat transfer to the feed water. This increased heat transfer consequently i ncreas ed the water temperature, causing the rate of evaporated water to increase, resulting in

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80 an overall increase in distilled water. I ncreasing the difference between the water tempe rature and cover temperature le d to an increase in the distilled water. Figure 6 23 Water temperature and glass temperature. For the experiment, reference data was taken as, Experiment time is from 9 am to 4 pm Feed water depth in the basin=1 cm. Glass cover slope = 38 degrees. The basin box wa s 2 m length and 0.5 m width; Area of the basin =2*0.5=1m 2 The g lass cover area wa s 1.4m 2

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81 The glass cover thickness wa s 4 mm. There was no temperature gradient through the cover due to the small thickness The experiment was done on a cloudy day. Figure 6 24 Reference experimental Solar Still distilled water [40]. The distilled water in this reference experiment fluctuate d due to fluctuation in the weather conditions during the experiment. The data taken was in (ml) per hour 6.3 Comparing the results C omparison of the modeling results of the PV solar powered desalination approach and Solar St ill approach are given in the figure 6.25, and the comparison of the experimental results of the both approaches are shown in the figure 6.26 The mass of the feed water use d in the solar still approa ch was constant; = 0.01 m 1 m 2 = 0.1 m 3 = 10 liters.

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82 While, t he feed water flow rate in the PV powered desalination approach was 0.018 kg/s =0.018 kg/s 3600 s/hr= 64.8 kg/hr = 64.8 liter/hr. in one hour. Figure 6 25 Comparing the freshwater results from the PV solar modeling approach with th e freshwater from Solar Stills m odeling for Seawater. The modeling of the distilled water of PV p owered approach was done in the same period that the modeling of the solar still was done ( 8 am to 5 pm ). It can be seen that the two approaches have a different behavior with time. The water production from the PV powered system method was not affected by ambient conditions because it was connecte d to the batt eries, which compensat ed for the solar energy available. On the other hand, in the solar was affected by change in the solar energy available.

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83 In the experiment, the differ ence between the two approaches was observed. The experiments for both methods were done in the same weather conditions .The experiments were made in a Figure 6 26 Comparing the freshwater results from the PV solar experimental approach with th e freshwater from Solar Stills e xperimental for Seawater As seen in the above figure, each approach had difference results. The difference between the two methods was caused by a variation in the weather conditions durin g the day. It can also be seen that the fresh water production from the PV powered desalination method was approximately linear and gave a steady daily production while the solar still daily production fluctuated with the time due to the weather conditions

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84 CHAPTER VII DISCUSSION AND CONCLUSION 7.1 Discussion In this research project, the numerical analysis of the basic solar desalination approaches was established and the theoretical results were compared with results obtained from the experimen t. Using the results from this research, the following could be concluded : The essential factor affecting the productivity of the solar still was the available solar energy. The water from the solar still increased in proportion to the amount of available solar energy. The performance of the PV solar powered desalination method was not affected by the variation of solar radiation, because it was connected to batteries to compensate the varia tion in available solar energy. When the temperature differences between the water interface and the glass cover in the solar still increased, the amount of the fresh water production increased. The maximum amount of the fresh water obtained from the solar still occurred during the period w hen the solar radiation was high est while the distilled water from the PV solar method was approximately constant. The deviation between the experimental and theoretical results for the solar desalination was due to the following reasons. The equations t hat were used in the calculations did not cons ider the heat losses due to the saturated water leakage from the solar still When the vapor pressure in the solar still was more than the ambient pressure, the saturated air leaked to the outside. The in coming air from the surroundings to the still was not saturated and it took time to be heated and then saturated This le d to a reducution of the

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85 distilled water of solar still. This was not considered in the numerical solution that p redicted the production rate s. And t he numerical calculations of the PV solar approach did not consider the changes in wind speed during the one hour testing period. 7.2 Conclusion Using the PV solar desalination system could provide a steady quantity of drinkable water for a small community and for people who live in regions with impure water sources. Add itionally, communities having difficulty in accessing local electricity or a lack of electrical power would benefit from solar desalinatio n Also, the PV solar desalination was a co ntinuously operating system throughout the day and it could be running continuously throughout the year. 7.3 Future Direction This research represents a basic step and study towards the development of a solar desalination system In the future, the study should consider the following points: Scaling the systems to increase the water flow rate produces from the system.

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86 REFERENCES [1] "Desalination by the Numbers," International Desalination Association, [Online]. Available: http://idadesal.org/desalination 101/desalination by the numbers/. [Accessed 28 January 2017]. [2] "Desalination industry enjoys growth spurt as scarcity starts to bite," Global Water Intelligence, [Online]. Available: https://www.globalwaterintel.com/desalination industry enjoys growth spurt scarcity starts bite/. [Accessed 26 January 2017]. [3] "Desalination: A National Perspective," National Academy of Sciences Press, Washington, D .C., 2008. [4] "Drinking Water Sources, Sanitation and Safeguarding," The Swedish Research Council Formas, 2009. [5] "History of water treatment," Lenntech, [Online]. Available: http://www.lenntech.com/history water treatment.htm. [Accessed 27 Janua ry 2017]. [6] Math Works, "Simscape/ Model and simulate multidomain physical systems," Math Works, 2016. [Online]. Available: https://www.mathworks.com/products/simscape.html. [Accessed 5 January 2017]. [7] "National Weather Service, Sea Water," US Dept. of Commerce, National Oceanic and Atmospheric Administration, [Online]. Available: http://www.srh.noaa.gov/srh/jetstream/ocean/seawater.html. [Accessed 9 January 2017]. [8] "Ocean Health Chemistry of Sea W ater," Ocean plasma, [Online]. Available: http://oceanplasma.org/documents/chemistry.html. [Accessed 7 February 2017]. [9] "Physical and Chemical examination," in European Standards for drinking Water, 2nd ed., Geneva, World Health Organization, 1970, pp 36 37. [10] "Water Desalination Processes," American Membrane Technology Association (AMTA). 2016. [Online]. Available: http://www.amtaorg.com/Water_Desalination_Processes.html. [Accessed 28 January 2017]. [11] "Water Desalination using Renewable E nergy | Technology Brief," 2012. [Online]. Available: http://www.irena.org/DocumentDownloads/Publications/Water_Desalination_Using_ Renewable_Energy_ _Technology_Brief.pdf. [Accessed 5 February 2017]. [12] "Water Scarcity, water & poverty, an issue of li fe & livelihoods," FAO Water, 2015. [Online]. Available: http://www.fao.org/nr/water/issues/topics_scarcity_poverty.html. [Accessed 12 January 2017].

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87 [13] "Why is the ocean salty?," National Ocean Service, National Oceanic and Atmospheric Administration U. S. Department of Commerce, [Online]. Available: http://oceanservice.noaa.gov/facts/whysalty.html. [Accessed 5 February 2017]. [14] [Online]. Available: http://www.cfdyna.com/Notes/ViewFactors.pdf. [Accessed 6 January 2017]. [15] B. D. Gupta, T. K. Mandraha, P. j. Edla and M. Pandya, "Thermal Modeling and Efficiency of Solar Water Distillation: A Review," American Journal of Engineering Research (AJER), vol. 02, no. 12, pp. 203 213, 2013. [16] D. Bonkoungou, Z. Koalaga and D. Nj omo, "Modelling and Simulation of photovoltaic module considering single diode equivalent circuit model in MATLAB," International Journal of Emerging Technology and Advanced Engineering, vol. 3, no. 3, pp. 493 502, 2013. [17] D. Hillel and E. Feinerman "Salinity Management for Sustainable Irrigation: Integrating Scie nce, Environment, and Economics ," The International Bank for Reconstruction and Development/ The World Bank, Washington D.C., 2000. [18] D. Mowla and G. Karimi, "Mathematical modelling of solar stills in Iran," Solar Energy, vol. 55, no. 5, pp. 389 393, 1995. [19] DAVID H. MARKS et al, Committee to Review the Desalination and Water Purification Technology Roadmap, Washington, D.C.: THE NATIONAL ACADEMIES PRESS, 2003. [20] F. P. INCROPERA, D. P. DEWITT, A. S. LAVINE and T. L. BERGMAN, Fundamentals of Heat and Mass Transfer, Hoboken: John Wiley & Sons, Inc., 2011. [21] G. Anderson, "Seawater Composition," Marine Science, 8 October 2008. [Online]. Available: http://www.mari nebio.net/marinescience/02ocean/swcomposition.htm. [Accessed 28 December 2016]. [22] G. E. Ahmad and J. Schmidb, "Feasibility study of brackish water desalination in the Egyptian deserts and rural regions using PV systems," Energy Conversion and Managem ent, vol. 43, no. 18, p. 2641 2649, 2002. [23] G. E. Ahmed and M. A. Mohamad, "Use of PV systems in remote car filling stations," Energy Conversion & Management, vol. 41, no. 12, pp. 1293 1301, 2000. [24] H. Cooley, P. H. Gleick and G. Wolff, "DESALINATION, WITH A GRAIN OF SALT A CALIFORNIA PERSPECTIVE Appendix A," PACIFIC INSTITUTE, Okland, 2006. [25] H. Ettouney, "Conventional Thermal Processes," in Seawater Desalination, Springer Berlin Heidelberg, 2009, pp. 17 40.

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88 [26] H. J. Krishna, "Introduction to Desalination Technologies," [Online]. Available: http://www.twdb.texas.gov/publications/reports/numbered_reports/doc/r363/c1.pdf. [Accessed 24 January 2017]. [27] H. Perlman, "The USGS Water Science School The World's Water," USGS, 2 De cember 2016. [Online]. Available: http://water.usgs.gov/edu/earthwherewater.html. [Accessed 1 January 2017]. [28] I. U. Haruna, M. Yerima, A. D. Pukuma and I. I. Sambo, "Experimental Investigation o f t he Performance," INTERNATIONAL JOURNAL OF SCIENTIFIC & TECHNOLOGY RESEARCH, vol. 3, no. 3, pp. 169 174, 2014. [29] J. A. Duffie and W. A. Beckman, Solar Engineering of Thermal Process, Hoboken: John Wiley and Sons Inc., 2013. [30] J. C. d. G. M. A. P. G. J C. Torchia Nez, "Thermodynamics of a Shallow Solar Still," Scientific Research Publishing Inc., vol. 6, pp. 246 265. [31] J. H. Watmuff, W. W. Charters and D. Proctor, "Solar and wind induced external coefficients Solar collectors," Revue Internationale d'Heliotechnique, vol. 2, p. 56, 1977. [ 32] J. Hamilton, "Careers in Solar Power," U.S. Bureau of Labor Statistics, June, 2011. [33] J. Murray, Chpt 4: Major Ions Of Seawater, University of Washington: Lecture, 2004. [34] L. D. Paulson, "What Is Brackish Water," RWL Water, 29 September 2014. [Online]. Available: https://www.rwlwater.com/brackish water/. [Accessed 28 December 2016]. [35] LINDASTCYR, "WORLD WATER DAY: 10 PLACES MOST IN NEED OF CLEAN WATER," ecorazzi, 22 March 2012. [Online]. Available: http://www.ecorazzi.com/2012/03/22/ world water day 10 places most in need of clean water/. [Accessed 30 December 2016]. [36] M. A. Eltawil, Z. Zhengming and L. Yuan, "RENEWABLE ENERGY POWERED DESALINATION SYSTEMS: TECHNOLOGIES AND ECONOMICS STATE OF THE ART," in Twelfth International Wat er Technology Conference, IWTC12 2008,, Alexandria, Egypt, 2008. [37] M. G. Buonomenna, "Membrane processes for a sustainable industrial growth," The Royal Society of Chemistry, vol. 3, no. 17, pp. 5694 5740, 2013. [38] M. van der Hoeven, Solar Energy Perspectives, INTERNATIONAL ENERGY AGENCY, 2011. [39] O. O. Badran and M. M. Abu Khader, "Evaluating thermal performance of a single slope solar still," in Heat and Mass Transfer, Verlag, Springer, 2007, p. 985=995.

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89 [40] of Technology, Izmir, Turkey. [41] R. A. Messenger and J. Ventre photovoltaic S ystems Engineering, 2nd ed., Boca Raton; London; New York; Washington, D.C.: CRC Press LLC, 2004. [42] Available: http://earthobservatory.nasa.gov/Features/EnergyBalance/p age4.php. [Accessed 11 February 2017]. [43] R. V. Dunkle, "Solar water distillation: the roof type still and a multiple effect diffusion still," International Development in Heat Transfer, vol. 5, pp. 895 902, 1961. [44] S. Skogestad, CHEMICAL AND ENERGY PROCESS ENGINEERING, Boca Raton: CRC Press, 2009. [45] Susan, "Shine On: An Introduction to Solar Power," Just Energy, 20 June 2013. [Online]. Available: http://www.justenergy.com/blog/shine on an introduction to solar power/. [Accessed 7 February 2017].