Citation
Design and evaluation of a self positioning mechanical solar concentrator to boil water and to produce work

Material Information

Title:
Design and evaluation of a self positioning mechanical solar concentrator to boil water and to produce work
Creator:
Yu, Hang ( author )
Place of Publication:
Denver, CO
Publisher:
University of Colorado Denver
Publication Date:
Language:
English
Physical Description:
1 electronic file (51 pages). : ;

Subjects

Subjects / Keywords:
Solar concentrators -- Efficiency ( lcsh )
Genre:
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )

Notes

Review:
This work consists of a new design of a solar concentrator tailored to two main applications: (1) to boil and produce drinking water; (ii) to evaluate the energy balance done by the system. This research includes a design of the tracking system used to focus the solar rays. The tracking system is intended to run unattended and automatically tracking the sun exclusively through mechanical means without requiring electric power. The design consists of a Fresnel lens, a moving frame, a track, a retaining mechanism, and a solar collector. The Fresnel lens focuses the solar energy into a circular spot at the collector; the frame holds the collector, keeping it aligned as it rotates with the lens; the track guides the farm keeping it oriented perpendicular to the sun; the solar collector receives the sun rays and releases the retaining mechanism, allowing the lens to rotate to the next location. The cycle repeats and the farm tacks the sun along the day. This work studies the performance of the solar collector. The collector receives the energy of the sun and produces steam by boiling water inside the collector. The pressure build up from the steam can be used to produce work, and after vented to the atmosphere, the steam can collected as drinking water. The system was evaluated experimentally and the results may serve as a basis for more comprehensive modeling and optimization to be performed in the future.
Thesis:
Thesis (M.S.)--University of Colorado Denver. Mechanical engineering
Bibliography:
Includes bibliographic references.
General Note:
Department of Mechanical Engineering
Statement of Responsibility:
by Hang Yu.

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University of Colorado Denver
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|Auraria Library
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903215491 ( OCLC )
ocn903215491

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Full Text
DESIGN AND EVALUATION OF A SELF POSITIONING MECHANICAL SOLAR
CONCENTRATOR TO BOIL WATER AND TO PRODUCE WORK
by
HANG YU
B.E., Xihua University, China, 2012
A thesis submitted to the
Faculty of the Graduate School of the
University of Colorado Denver in partial fulfillment of
the requirements for the degree of
Master of Science
Mechanical Engineering Program
2014


This thesis for the Master of Science degree by
Hang Yu
has been approved for the
Mechanical Engineering Program
by
L. Rafael Sanchez Vega, Chair
Marc Ingber
Kannan Premnath
7/24/2014


Yu, Hang (MS, Mechanical Engineering)
Design and Evaluation of a Self Positioning Mechanical Solar Concentrator to Boil Water
and to Produce Work
Thesis directed by Associate Professor L. Rafael Sanchez Vega
ABSTRACT
This work consists of a new design of a solar concentrator tailored to two main
applications: (i) to boil and produce drinking water; (ii) to evaluate the energy balance
done by the system. This research includes a design of the tracking system used to focus
the solar rays. The tracking system is intended to run unattended and automatically
tracking the sun exclusively through mechanical means without requiring electric power.
The design consists of a Fresnel lens, a moving frame, a track, a retaining
mechanism, and a solar collector. The Fresnel lens focuses the solar energy into a circular
spot at the collector; The frame holds the collector, keeping it aligned as it rotates with
the lens; The track guides the frame keeping it oriented perpendicular to the sun; The
solar collector receives the sun rays and releases the retaining mechanism, allowing the
lens to rotate to the next location. The cycle repeats and the frame tracks the sun along
the day.
This work studies the performance of the solar collector. The collector receives
the energy of the sun and produces steam by boiling water inside the collector. The
pressure build up from the steam can be used to produce work and, after vented to the
atmosphere, the steam can be collected as drinking water. The system was evaluated
experimentally and the results may serve as a basis for more comprehensive modeling
and optimization to be performed in the future.
m


The system was designed keeping in mind portability, low cost, accessibility,
simple to maintain and easy to repair. It may be particularly useful to people living in
sunny areas with limited electricity and/or drinking water.
The form and content of this abstract are approved. I recommend its publication.
Approved: L. Rafael Sanchez Vega
IV


TABLE OF CONTENTS
CHAPTER
I. INTRODUCTION....................................................1
Purpose of the Study............................................2
Scope of the Study..............................................2
II. REVIEW OF THE LITERATURE........................................4
III. DESCRIPTION OF THE COMPONENTS OF THE PROPOSED SOLAR
TRACKING SYSTEM.................................................6
Fresnel Lens....................................................6
Sun Energy along its Path.......................................9
Solar Collector................................................13
IV. THERMODYNAMIC ANALYSIS OF THE SOLAR CONCENTRATOR ...15
V. EXPERIMENTAL EVALUATION OF THE SOLAR CONCENTRATOR ...22
Amount of Heat Absorbed by the Water...........................22
Quantification of Work Performed ..............................23
VI. HEAT TRANSFER APPROACH USING FINITE ELEMENT METHODS............24
Building Geometry..............................................25
Physics Formulation of the Model: Navier - Stokes Equation.....26
Heat Equation..................................................27
Initial Values and Boundary Conditions.........................28
Heat Transfer with Phase Change................................28
Mesh and Study Type............................................29
FEM Results....................................................30
v


Limitations of the FEM Model...............................33
VII. CONCLUSIONS..............................................35
REFERENCES....................................................37
APPENDIX......................................................38
vi


LIST OF TABLES
TABLE
1. Material Properties of Fresnel Lens........................................9
2. Example of NREL Radiation Data Representative of a Sunny Day at Broomfield, CO..
Radiation from the Sun is Perpendicular to the Lens.......................12
3. Properties of Two-Phase Water-Vapor........................................21
4. Summary of the Calculated Results Based on the Experimental Parameters.....22
vii


LIST OF FIGURES
FIGURE
1. Cross Sectional View of Fresnel Lens........................................7
2. Fresnel Lens with Lens Area of 0.83 m and Focal Length of 34 inches.........8
3. Description of the Suns Path..............................................10
4. Altitude Angle for July 15, 2014...........................................10
5. Azimuth Angle for July 15, 2014............................................11
6. Solar Collector............................................................13
7. Closer View of the Solar Collector System..................................14
8. 2D Sketch of the Solar Collector...........................................15
9. thep-v Diagram for Two-Phase Water.........................................18
10. Temperature as a Function of Pressure for Two-Phase Water..................19
11. Boiling Curve for Water at Atmospheric Pressure............................24
12. FEM COSMSOL Geometry Model.................................................26
13. FEM Mesh of Solar Concentrator.............................................30
14. @ t = 0^, the Heat Source Starts Heating the Surface and the Contact Surface
Reaches the Temperature of 1000 C.........................................31
15. @ t = 3755, the Heat Flux through Convection Conducts Heat to the Fluid....31
16. @ t = 7505, Vapor Starts to Generate Locally, Nucleate Boiling.............32
17. @ t = 11255, More Vapor is Generated.......................................32
18. @ t = 15005, Boiling Becomes Intensive, Further Increasing Vaporization. This
Behavior is Representative of Film Boiling.................................33
viii


CHAPTERI
INTRODUCTION
A low cost, small scale throughput device, capable to concentrate energy from the
sun and capable to track the sun mechanically (without using electric power), may satisfy
many needs around the world. For instance, it could be used as a solar cooker, as a water
boiler, as a disinfectant of medical instruments, etc. It can be used to improve the
conditions of people living in remote or arid areas where clean water may be scarce, or as
a clean energy source to help reduce the need for deforestation. It may serve as a tool to
survival in emergency cases; as for individuals lost in the wilderness, or lost at sea.
Tracking solar concentrators on the market today are typically electrically
powered through batteries or directly by the electrical grid. They are driven by motors
with feedback sensors and controllers. These systems tend to be expensive and when used
to produce electricity, economies of scale often require high throughput power. Their use
may be limited to large sunny areas where control and access to the electric power grid
may present serious issues.
Solar panels are commercially available for small scale applications (less than 1
KW). Nevertheless, the approach to solar capturing by the Fresnel lens method proposed
here, and those using solar panels present significant differences. The electrical output
from the array of solar cells requires accessories such as batteries and inverters, which
drive the cost higher for these units. Furthermore, solar panels are of difficult repair if
they malfunction during use. The Fresnel method proposed here is exclusively
mechanical, and the very high localized temperatures reached at the focus may be an
advantage over solar panels for some applications. The Fresnel system was designed as a
1


low cost device with ease of maintaining and repairing, using readily available
economical mechanical components.
This work builds from past work of Dr. Sanchez Vega (Advisor) and Noe
Villagrana (MS graduate student) at the ME Dept. University of Colorado Denver [1],
Noe and his advisor, Dr. Sanchez Vega, built the first version of a self tracking solar
concentrator based on a Fresnel lens. The preliminary version provided the basis to
demonstrate the feasibility of several components of the system. In this work, Dr.
Sanchez and his graduate student Hang Yu redesigned and built a second prototype. The
second version included significant improvements and additions to the first version and
its analysis is the basis for this study.
Purpose of the Study
This work consists of the analysis and experimental study of a solar concentrator
capable of tracking the sun mechanically. The tracking movement is integrated with two
main applications: (i) to produce drinkable water by boiling, (ii) to estimate the efficiency
and the work done by the system during operation. The device is designed for simplicity
and portability, of easy repair and accessible. This work is envisioned as an addition to
sustainable or clean energy methods. It is intended to serve a large segment of the world
population with limited access to electrical energy, or drinking water. Upon successful
completion of this project, an array of additional applications could be developed; some
of them readily, such as solar cooking, autoclaves for medical instrument disinfection, etc.
Scope of the Study
This study is limited to an approximate analysis of the feasibility of the system,
and to an approximate experimental evaluation of the main parameters. The system
2


receives the sun rays and can reach very high temperatures at the focus (in excess of 1000
C The collected solar energy is used to power the mechanical movement of the lens
and to produce water vapor. The analysis focuses on the following items; (i) The
efficiency of the system in capturing the sun energy required producing steam as a means
to obtain drinking water, (ii) the estimating of the work produced by the system, (iii) the
analysis of the movement and repositioning of the frame.
The analysis includes an estimate of the heat conduction and convection
mechanisms, and the evaluation of the properties of water (pressure, or temperature,
specific volume, etc.) at the water-vapor phase. The analytical approaches are based on
general thermodynamic principles, with inclusion of Finite Element Methods (COSMOL).
Experimentally, the amount of work transmitted by the system was measured
through the amount of compression of a spring. Pressure was monitored using a general
purpose pressure gage. Temperature was monitored externally at various locations. The
change in volume was determined by measuring the displacement of the piston. The
overall assessment of the efficiency of the system was based on the amount of water
vaporized or boiled on a full cycle, compared to the amount of sun energy received.
3


CHAPTER II
REVIEW OF THE LITERATURE
This work is a continuation of Dr. Sanchez Vega and his MS student, Noe
Villagrana, at the ME Dept. University of Colorado Denver [1], This preliminary work
served to prove the feasibility of several components of the system.
Literature abounds about systems designed to capture and use solar energy. Xie et
Al. wrote an extensive review on the recent developments in solar concentrators. Their
review summarizes Fresnel lenses systems and its applications to solar power, hydrogen
generation, photo-bio reactors, etc. [2], Fresnel lenses are among the most popular solar
concentrator lenses due to their low mass, lightness, and small thickness [3], Extensive
mechanical, physical and optical properties of Fresnel Lenses are available from Fresnel
lens manufactures such as 3HLens Co. [3] and Fresnel Technologies Co. [4], Yinghao
Chu published a review overviewing different solar energy technologies [5], He focused
on Concentrated Solar Power (CSP) and Photovoltaic Solar Panels (PV) as two of the
most mature technologies. He also included Solar Thermoelectricity Systems (STA), dye
sensitized solar cell (DSPV) and concentrated photovoltaic systems. Sahoo et Al.,
published an Experimental investigation of convective flow boiling in the absorber tube
of the linear Fresnel reflector solar thermal system [6], He presented Linear Fresnel
Reflection (LFR) technologies with promising application in solar thermal systems.
Yousif A. Abakr, and Lee Yeu Sheu designed a water boiler with a tracking system.
Their tracking system was controlled by sensors and electric motors programmed through
a main controller [7],
4


Christina Awad published a MS thesis on Enhancing the Solar Water Disinfection
(SODIS) Method Using a Fresnel Lens [8], She discussed the parameters regarding the
solar power necessary for disinfection of medical instruments. M. Mahmoudi, and A.
A.El-Sattar Mohamed studied the utilization of a Fresnel Lens in water heating and
dehumidification process [9], They used a Fresnel lens for heating saline water for water
purification. G. A. Madhugiri and S. R. Karale wrote a review on High Solar Energy
Concentration with a Fresnel lens [10], Their paper was focused on the Solar Energy high
temperatures using parabolic solar concentrator, Fresnel lens, Reflecting materials and
solar tracking. The performance of each concentrator was explained and compared.
5


CHAPTER III
DESCRIPTION OF THE COMPONENTS OF THE PROPOSED SOLAR
TRACKING SYSTEM
The basic components of the solar concentrating tracking system consist of: (i) an
element able to concentrate the suns rays; (ii) an element capable of absorbing the solar
energy while minimizing loses due to reflection, and heat transfer; (iii) a moving frame
actuated by the thermal energy captured and capable of following the suns path. In this
study, a Fresnel lens is used as a concentrating medium. As the light passes through the
lens area, it focuses it at a circular spot at the collector where light is converted into heat.
A medium inside the collector captures the heat and expands as the pressure (and
temperature) increases. At a desired pressure (or temperature) setting, the resultant
volumetric expansion results in the releasing of a retaining mechanism, allowing the
frame to rotate. The frame holds the lens and the collector together. As the frame rotates,
the tracking mechanism keeps them aligned perpendicular to the sun at all times.
Fresnel Lens
A Fresnel lens is a lens composed of many minute concentric annular sections
that can concentrate the suns rays [1], Fresnel Lenses where developed in 1822 by a
French physicist named Augustine-Jean Fresnel. By using only the refracting sections of
a spherical lens and laying them flat, Fresnel made a flat lens capable of concentrating the
solar rays in a fashion similar to a standard spherical lens with significant gains on
reduced size and weight (Figure 1).
6


Figure 1. Cross Sectional View of Fresnel Lens
There are four types of Fresnel lenses: spot, linear, cylindrical and spherical. Spot
and linear lenses are the most commonly used lenses in solar power applications, and a
spot Fresnel lens is used in this work. A spot Fresnel lens takes the light from the sun and
concentrates it to a singular point called the focal point. For maximum efficiency, the lens
must be perpendicular to suns rays. The distance of the focal point from the lens face is
called the focal length (Figure 1).
The lens used in this study was made of PMMA (Polymethyl methacrylate), also
called Acrylic glass. This material is widely used for solar gathering applications. The
lens is circular with a focal length = 880 mm. It was delivered cut 1 m by 1 m square. The
resulting effective Fresnel lens area was 0.83 m (Figure 2).
7


Losses due to light absorption or reflection are small, with 92 % transmittance
reported by the manufactures [2], The general specifications are shown in the Table
below.
Figure 2. Fresnel Lens with Lens Area of 0.83m and Focal Length of 34 inches
8


Table 1: Material Properties of Fresnel Lens
Fresnel Lens Material PMMA Acrylic
Index of Refraction 1.49
Transmittance 92%
Thickness 3 mm
Groove Pitch 0.5 mm
Focal Length/Magnification 880 mm
Tensile Modulus 325-470 xlO3 psi
Flexural Modulus 390-470 xlO3 psi
Hardness M80-M100 (Rockwell)
Thermal Expansion 76 xlO-6/C
Specific Gravity 1.19
Effect of Sunlight none
Sun Energy along its Path
The path followed by the sun is well known. It is typically given by the Azimuth
and the Altitude (or Elevation) angles (Figure 3). The Azimuth angle is measured from
North following a clockwise direction, and the Altitude is measured from the horizon.
Another commonly used angle, the Zenith angle, is the complement to the Altitude angle
measured from the vertical. These angles can be calculated using solar position
algorithms, such as those developed by NREL [11], However, the sun position data is
readily available from USNO [12] and will be used here.
9


The data includes the azimuth and the altitude (or elevation) angles at any desired
interval within 1-120 minutes at any desired location in the USA. The sun position data
corresponding to July 15, 2014 is shown in the Appendix.
Vertical
Figure 3. Description of the Suns Path
Figures 4 and 5 show the plots of the azimuth and the altitude angles
corresponding to July 15, 2014. The tracking mechanism was adjusted to position the
frame according to these angles.
Altitude Angle
Angle (Deg}
80 i----
Figure 4. Altitude Angle for July 15, 2014
10


Angle (Deg) Azimuth Angle
Figure 5. Azimuth Angle for July 15, 2014
On average about 1400 W/m2 from the sun reaches the top of our atmosphere.
Part of that energy is reflected back into space or absorbed by our atmosphere. The
Denver, Boulder area, receives around 700 W/m on average. NREL [13] maintains
national data bases of the amount of solar radiation received anywhere in the country (see
USAF#724699 for Broomfield-Boulder). The data bases are very complete. They
include experimental and modeled hourly average radiation under sunny and cloudy days.
Table 2 shows the experimental data corresponding to 60 mins averages of solar
radiation received at the experimental location. Radiation data with the lens perpendicular
to the sun (METSTAT Dir) was especially useful to our study. The data shows a typical
sunny day, although some atmospheric attenuation (light clouds, humidity, etc.) may
show in the statistical averages. Hours between 9:00 am and 4:00 pm are particularly
suitable for sun radiation collection.
11


Table 2: Example of NREL Radiation Data Representative of a Sunny Day at Broomfield,
CO. Radiation from the Sun is Perpendicular to the Lens
MM/DD HH:MM Zenith (deg) Azimuth (deg) ETRN METSTAT Dir
8/13 6:00 86 74 1076 147
8/13 7:00 76 82.5 1331 566
8/13 8:00 64.6 92 1331 759
8/13 9:00 53.3 102.7 1331 852
8/13 10:00 42.5 115.9 1331 902
8/13 11:00 33.2 134.3 1331 930
8/13 12:00 27 160.8 1331 943
8/13 13:00 26.4 193.2 1331 943
8/13 14:00 31.7 221.3 1331 828
8/13 15:00 40.6 241 1331 531
8/13 16:00 51.2 254.9 1331 749
8/13 17:00 62.5 265.9 1331 634
8/13 18:00 73.9 275.6 1331 562
8/13 19:00 84.9 284.8 1298 140
ETRN: Amount of solar radiation received on a surface normal to the sun at the top of the
atmosphere during the 60-minute period ending at the timestamp (W/m ).
METSTAT Dir: Amount of solar radiation received in a collimated beam on a surface
normal to the sun during the 60- minute period ending at the timestamp (W/m ).
12


Solar Collector
The solar collector receives the radiation from the sun and converts it into heat
(Figures 6, 7). The Fresnel lens itself is not sensitive to small changes on the angle of
incidence from the sun [4], However, the collector must be properly positioned
(perpendicular to the sun) and shaped to minimize reflection. The visual brightness
(reflection) of the collector used here was low enough to be considered satisfactory, but
no attempts were made here to optimize its geometry.
Figure 6. Solar Collector
13


Figure 7. Closer View of the Solar Collector System
The orientation of the collector, perpendicular to the sun, was located by the
tracking mechanism within 0.1 degree at several specified locations. The concentrated
beam of the sun approximately located at the center of the collector at all times during the
duration of the experiments. This provided a satisfactory assessment of the tracking
mechanism. The system was partially isolated; mainly to avoid wind convective heat
loses.
As the collector is heated by the concentrated beam of the sun, the pressure and
temperature increase. At a measured level, the valve opens to the atmospheric pressure
and aggressive boiling occurs, vaporizing a significant amount of water.
14


CHAPTER IV
THERMODYNAMIC ANALYSIS OF THE SOLAR CONCENTRATOR
The model of the solar concentrator is shown in Figure. 8. The concentrator is
tilted by the altitude angle, where the central container receives the heat perpendicular to
the rays of the sun. Initially, the container is completely filled with water at ambient
temperature.
Figure 8. 2D Sketch of the Solar Collector
As the heat is absorbed, the water and formed vapor expand against the spring
loaded piston. The movement of the piston actuates the tracking mechanism. Also, at a
set piston displacement the valves open, releasing the vapor. The displacement of the
piston increases the volume of the container. Since the spring compresses upon
displacement of the piston, the spring force and therefore the pressure on the fluid
increase. The spring can be adjusted to produce a specified pressure at the displacement
15


corresponding to the releasing of the vapor. Since the temperature of the water-vapor
mixture increases with pressure, setting the spring also adjusts the desired final
temperature at which the vapor is released. Since the amount of water vapor depends on
the final temperature, the vaporization is effectively controlled by the amount of
compression of the spring.
The input power received by the Fresnel lens is taken from the NREL data base at
month, day and hour corresponding to our experimental conditions. For a flat plate
located at the focus, the lens is reported to concentrate the suns beam to a circular area
smaller than 1 inch in diameter. However, there is a trade off on the amount of light
received and reflected by a flat surface. The geometry of the container at the area of
incidence was less reflective, but the focal area was larger. Due to some reflection, the
actual focal spot was difficult to calculate accurately. It was visually estimated as a
circular section around 1.5 inch diameter.
Under the assumptions above, an example of the estimate of the heat rate
produced from the radiation energy of the sun is given as:
At August 13, from 10:00 11:00 am, sunny skies, sun energy perpendicular to
the lens at Broomfield, CO (Table 2):
9Sun = 902 W/m2
92% transmittance through the lens with an area = 0.83 m gives:
qlem= 902 (0.83)(0.92)= 688 W
The energy received in one hour is = 688 (3600) = 2476.8 kJ/hr.
16


Ideally, the energy required to vaporize water at 100 C starting from 25 C is
2571 kJ/kg. Assuming no losses, at this radiation level the time to produce one gallon of
water would take around 4 hours for a lens this size.
Estimating a concentrated spot area = 1.77 in2',
0.83(1)2
The concentration at the focus is------.0254----720 times. This gives a flow
1.77
rate at the focus of around qfocm =720(688) = 5(10)5 W
Also. 4v,,=^|f = 6(10)!Vm2
This is an upper estimate which does not include the amount of energy reflected
by the surface of the container. An experimental estimate for reflection will be proposed
below.
Part of the heat is absorbed by the container and water (liquid and vapor) and part
is absorbed but lost through conductive and convective heat losses (container radiation
effects are considered small and were neglected):
Qin Ec+Ew+W +QcodloSS Qconvloss
Where Ec = Energy absorbed by the container,
Ew = Energy absorbed by the water and vapor,
W = Work done by the system against the spring,
Qcondloss= Losses due to conduction from the container to the frame,
Qconvloss = Losses due to convection with surrounding air,
17


The energy absorbed by the container can be calculated using the specific heat of
each material making part of the container:
E=mcCcAT
Where mc,Cc are the mass and the specific heat.
The energy absorbed by the water was calculated from steam tables. The
approach is approximate, as those tables were determined under quasi-equilibrium
conditions. However, data from steam tables are considered more accurate than using
other models for water vapor, such as the ideal gas model, or the Van der Waals models.
Of interest in this study are the liquid and liquid vapor regions for water. Only a
very limited range of the p-v diagram (Figure. 9) will apply here. At the critical point,
water pressure is 22.1 MPa (647.4 K). In contrast, the pressure range used in this study
located between 0.1 MPa (atmospheric pressure) and 0.2 MPa (120.2 C ). Our region of
interest will be exclusively in the quality region.
Figure 9. the p-v Diagram for Two-Phase Water
18


For a pure substance, water vapor in quasi-equilibrium, the absolute pressure
and temperature are functions of each other; knowing one fully defines the other, as
shown in Figure 10.
Temperature (C)
Figure 10. Temperature as a Function of Pressure for Two-Phase Water
The initial conditions are defined at ambient temperature, atmospheric pressure
and with the container full of water. As heat is transferred, the temperature increases for
water to reach the saturated liquid curve. Further heating increases the temperature (and
pressure) with water becoming a two-phase fluid mixture in equilibrium.
Let:
vf = Specific volume of the saturated liquid,
vg = Specific volume of the saturated vapor,
mf = Mass in liquid phase,
m = Mass in vapor phase,
19


v = Specific volume for the two-phase liquid and vapor phase,
m= Total mass of the two-phase mixture.
The total volume is given by
mv =mfvf + mgvg,
The quality of the mixture, x, is given by:
m
*=,
m
Reordering:
v =vf + x(v vf), 0 The force applied to the spring by the system is:
F=ks(8 + 80),
Where ks is the spring constant, 8 = piston displacement, 8{ = spring preload.
Monitoring the displacement 8, gives the pressure P at the piston:
P=^+101325 = ^(^ + ^) +1Q1325 pa
^piston y
Where 8 = piston diameter and P = absolute pressure.
With the absolute pressure (and temperature) known as a function of the
displacement, we can find from the steam tables the amount of water vaporizing with
increasing pressure. The amount of heat transferred to the water- vapor mixture is given
by:
Qin water+vapor
u.
water+vapor
+ W
Where the internal energy U can be calculated from Table 3.
20


Table 3: Properties of Two-Phase Water-Vapor
Specific Volume (m3 /kg) Specific Internal Energy (kJ/kg)
P ,MPa T ,C vf uf l{g
0.1 99.6 0.001043 1.694 417.3 2506.1
0.12 104.8 0.001047 1.428 439.2 2512.1
0.14 109.3 0.001051 1.237 458.2 2517.3
0.16 113.3 0.001054 1.091 475.2 2521.8
0.18 116.9 0.001058 0.9775 490.5 2525.9
0.2 120.2 0.001061 0.8857 504.5 2529.5
Given the path between the initial and final (P, v) state conditions, the work done
by the system against the spring can be calculated:
v2
W=\Pdv
21


CHAPTER V
EXPERIMENTAL EVALUATION OF THE SOLAR CONCENTRATOR
Amount of Heat Absorbed by the Water
The following data apply to our experiment:
Total mass = m = 0.51 kg
Piston diameter = d= 1.125 in = 0.02858 m
Piston area = A = 0.994 in2 = 6.4153 (10)'4 m2
Spring constant = ks = 10.0 lbs./in = 1750 N/m
Free length = 3.61 in = 0.0917 m
Initial compressive preload =3.07z=0.078/w; S0 = 3.61-3.07 = 0.54 in = 0.0137 m
Final compression = 2.15 in = 0.055 m; 8 = 3.61-2.15 = 1.46 in = 0.037 m
Table 4: Summary of the Calculated Results Based on the Experimental Parameters
Initial Preloaded Final
Absolute Pressure (x 10 1MPa) 1.01 1.39 2.50
Temperature (C) 100.00 109.01 126.86
Piston Displacement ( x 10~2 m) 0 1.37 3.67
Spring Force ( x 10~6 N) 0 23.98 64.23
Total Volume (xlO 4 nr'') 5.30 5.39 5.54
Quality x (xl0~6) 0 5 30
uf Specific Internal Energy of liquid (kJ/kg) 418.75 456.97 532.89
Estimates from the steam tables data, show very sma 1 amounts of vaporization
are produced as the absolute pressure is increased to 0.25 MPa, and the temperature is
22


raised to about 126.8 C .This is also shown by the very small values for quality x,
meaning that most of the heat was absorbed at the liquid phase.
Upon opening of the valve, the pressure drops to 1 atmosphere and significant
vaporization occurs. The change in Enthalpy at the liquid (close enough to uf ) drops to
532.9-418.7 = 114.1 kJ/kg. The latent energy at 100 C is 2257 kJ/kg and the mass
114 1
evaporated becomes =------(0.51)=0.0258Ag\ More water is added and the cycle
repeats. The net mass evaporated per cycle is ~ 0.026 kg. Around 8 cycles repeated in one
hour, giving -0.21 kg/hr of distilled water. The ideal estimate in page 16 can be used to
estimate the efficiency of the system:
Quantification of Work Performed
The work performed by the system to the spring upon expansion between the
initial and final states can be readily calculated:
2257
Efficiency
------:------100 = 21.8%
(2476.8/2571)
r = Q51 0101325 + 0250
(0.001089-0.00104)=4.40 / cycle
2
Which is small, but effectively operates the lever mechanism.
23


CHAPTER VI
HEAT TRANSFER APPROACH USING FINITE ELEMENT METHODS
The results above were determined assuming that the mixture was in quasi-
equilibrium. This assumption is challenged by the peculiarities of the actual phenomenon.
Boiling is significantly noticeable as soon as the sun beams are focused by the lens on the
container.
Figure 11 shows the boiling curve for water at O.lOIMPa (1 atm). The figure
shows the various heat transfer mechanisms for water, which depend on the heat intensity
and the differences of temperatures between the heat source at the collector spot and the
liquid.
Convection Nucleate Transition Film
Point A-Onset of boiling
Point B- Inflection point
Point C Critical heat flux
Point D- Leidenfrost point
Figure 11. Boiling Curve for Water at Atmospheric Pressure
Our estimate of the heat transfer at the focus given in page 15 was
24


Qfocus =6 (10)5W/m2 ;
Which is high enough for nucleate and film boiling.
These two boiling modes are also the most effective, resulting in heat transfer
rates high than those in conduction [14],
The figure makes obvious that quasi-equilibrium (which is the basis for the use of
steam tables) is not operative for this case. In fact, the measured amount of water
vaporized was significantly larger during experimentation that the one estimated in page
20 using steam tables.
FEM COMSOL was used in an effort to develop a more representative model.
Boiling does not happen in a closed container provided that it is in equilibrium. In a non-
equilibrium case as this, the container is intensely heated locally. The high temperatures
generated by the Fresnel lens result in easily noticeable boiling in the container.
Building Geometry
In the COMSOL model, the Heat Transfer in Fluids module is used to solve this
phenomenon. A domain that contains liquid (water) and vapor (steam) materials is set up
and the properties of the materials are selected via COMSOL materials library.
25


Figure 12. FEM COSMSOL Geometry Model
Physics Formulation of the Model: Navier Stokes Equation
The boiling phenomenon is governed by the Navier-Stokes equations. In an inertia frame
of reference, the Navier-Stokes equations general form is:
p[j^ + v-Vv^ = -Vp + V-a + f
Where v is the flow viscosity,
p is the fluid density,
p is the pressure,
/ is other body forces (per unit volume) acting on the fluid,
V is the delta operator.
Consider the velocity field and pressure in liquid phase is incompressible, the
Navier-Stokes equations can be derived (subscript L denotes liquid phase):
26


P,. ^r~ + P,. (ul V)WL = v [- pLI + vL (vm, + (VuL J )]+ pLg sin(a)
V-uL =0
Where pL is the fluid density (kghn3),
uL is the fluid velocity {mis),
pL is the liquid pressure (Pa),
a is the altitude angle {Deg),
vL is the viscosity (Pa-5).
For vapor phase, the Navier-Stokes equations can be solved as compressible
substance (subscript L denotes vapor phase):
c)t(
Pv^r~ + Pv{uL-V)uv =v'
ot
PVI + (Vl'r + (V"V )' )_|'V (V'uv )I
+ PvS sin
Spy
dt
+ V-(pvuv) = 0
Where pv is the vapor density (kg/m3),
uv is the vapor velocity (m/s),
pv is the vapor pressure (Pa),
a is the altitude angle {Deg),
vv is the viscosity {Pa 5),
is the bulk (second) viscosity {Pa 5).
Heat Equation
In general, 3-D heat equation is described as


Where Cp is the specific heat capacity (j /(kg-Kj),
k is the thermal conductivity (lV /(in K)).
Because the temperature at the liquid and vapor interface is at saturation
temperature, the heat equation can be solved by the vapor phase Navier Stokes
equations:
Initial Values and Boundary Conditions
The initial values of this model are set as all boundaries have the room
temperature 25C (298.15 K), and the heat source has a temperature of
1000C (1273.15 K) acting on the copper cup (a copper penny at the focus melts easily)
which is designed to stand the high temperature and conduct heat flux to the water. All
other boundaries are set as insulated.
Heat Transfer with Phase Change
In this model, the phase change is between liquid water and vapor, and the
parameters can be calculated by the parameters of two different phases as:
Cppv + cppv (iUy V)Tv = kvV2Tv + pvg sin(cr)
Where C/; is the specific heat capacity (./ /(kg- K)),
kv is the thermal conductivity of the vapor (lV /(in K)).
K-XK,
'Phase1
+ (l-x)Kphase2
CP=*C1
+ (1 x)C
28


+ (1 X) PPhased,
PhaseTL p,Phase!.
Where Cp is the specific heat capacity (j /(kg-Kj),
k is the thermal conductivity (fV /(m- K)),
p is the fluid density {kg/m3),
x
is the quality of the mixture,
CL is the latent heat distribution;
a is the Heaviside function, is the Dirac pulse, L is the latent heat.
dT
The two phases in this model are corresponding to liquid (water) phase and vapor
(steam) phase, which can be found in the material library.
Mesh and Study Type
In this model, a finer, physical-controlled mesh is used to conduct the Finite Element
Analysis calculation. There are 532 DOFs (plus 103 internal DOFs) to be solved in this
model. In order to show the transient process, a Time Dependent study type should be
selected to compute.
29


-L
1
3.5
3
2.5"
2
1.5
1
0.5
0"
-0,5
-1
-1,5
-2
-2.5l
-3
-3.5
n*-1--1--1--1--1--1---
-4-3-2-10 1 2 3
4
Figure 13. FEM Mesh of Solar Concentrator
FEM Results
The figure bellows show the evolution of the transient temperature distribution,
and the 2-D transient phase-change.
30


Figure 14. @ t = O.v, the Fleat Source Starts Fleating the Surface and the Contact Surface
Reaches the Temperature of 1000C
3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
-4 -3 -2 -1 0 1 2 3 4 0
Figure 15. @ t = 375s, the Heat Flux through Convection Conducts Heat to the Fluid
31


1
0.9
0.8
0,7
0.6
0.5
0.4
0.3
0.2
0.1
0
Figure 16. @ t = 750.v, Vapor Starts to Generate Locally, Nucleate Boiling
3
2.5
2
1.5
1
0.5
0
-0.5
-1
-1.5
-2
-2.5
-3
-4 -3 -2 -1 0 1 2 3 4 0
Figure 17. @ t = 1125s, More Vapor is Generated
M, 1
I
1
0,9
0,8
0.7
0,6
0.5
0.4
0,3
0.2
0,1
0
32


t-----------1-----------1----------1-----------1----------1-----------1-----------1----------n i
-4 -3 -2 -1 0 1 2 3 4 T 0
Figure 18. @ t = 15005, Boiling Becomes Intensive, Further Increasing
Vaporization. This Behavior is Representative of Film Boiling
The FEM results show that the system produces significant steam before opening
to the atmosphere. As long as the container is exposed to the sun, vapor is generated. The
pressure inside the container will be raised for as long as the vaporization is increased.
After the piston moves to a set distance, opening the valve to the atmosphere, the boiling
point decreases to 100 C and aggressive vaporization is observed.
Limitations of the FEM Model
This model is based on several assumptions:
1) The reflection caused by the copper surface has not been considered in this
model, which results in the solar energy loss and decrease in temperature applied
to the surface.
2) The model is solved in a 2D plane instead of a 3D model, which results in an
inaccurate quantitative outcome. Only qualitative conclusions can be
33


summarized from this model.
3) The radiation and convection from the other hot sides of surface to the liquid are
neglected, which also enhance the vaporization to form and produce vapor.
Despite the limitations above, this study shows a need to take into account the non-
equilibrium progression for this heat transfer case.
34


CHAPTER VII
CONCLUSIONS
1. The prototype of the Fresnel lens system demonstrated its feasibility on water
boiling applications. Although the efficiency of the current prototype (at around
21.8%) was rather low, this number has the potential for improvement through
better isolation and better design.
2. Modeling of the water boiling phenomenon was readily accomplished using steam
tables. However, the assumption of quasi-equilibrium required for these tables
was shown to depart from more sophisticated FEM modeling as well as from
experimental observations.
3. The amount of vaporization (0.21 kg/hr distilled water) estimated by steam tables
was relatively low. Although this estimate may be low, or more efficient, better
isolated systems can be implemented, this issue can also be addressed simply by
increasing the size of the Fresnel lens. Since the throughput increase to the square
of the length, an increase of 50% in length would more than double the area of the
lens. The use of square lenses, as opposed to the circular pattern used here, will
also increase throughput for the same frame size.
4. The tracking mechanism located the lens perpendicular to the sun for the tracking
range used. The lever system, enacted by the movement of the piston, could be
adjusted to fit this intended application. The transition from water to vapor, with
the corresponding increase of pressure under heat was a convenient method to
actuate the lever system.
35


5. The lens generates extremely high temperatures (in excess of 1000 C) at the
focus. These high temperatures can be used in other applications, for instance, in
the design of Autoclaves to disinfect medical instruments, to increase the
throughput of solar panels, etc. Other research areas of interest may include
accelerated fermentation through the application of heat to certain kinds of flora
for production of electricity, waste disposal through high level temperature
incinerators, etc.
36


REFERENCES
[1] Noe Villagana (Advisor: L. Rafael Sanchez Vega), Fresnel Solar Concentrator,
Master of Science Project Thesis, Mechanical Engineering, College of Engineering,
University of Colorado Denver, Denver, CO., August 2013.
[2] W.T. Xie et Al., Concentrated solar energy applications using Fresnel lenses: A
review, Elsevier, Renewable and Sustainable Energy Reviews, 15 (2011) 2588- 2606.
[3] www.BHLens.com.
[4] www. fresneltech. com.
[5] Yinghao Chu, Review and Comparison of Different Solar Energy Technologies,
Global Energy Network Institute (GENI), August 2011.
[6] Sahoo et Al., Experimental investigation of convective flow boiling in the
absorbertube of the linear Fresnel reflector solar thermal system, Solaris 2012 -India,
Varanasi, India, 7-9 Feb 2012.
[7] Yousif A. Abakr, Lee Yeu Sheu, Solar Water Boiler with Tracking System,
Taylors College Subang Jaya, Malaysia.
[8] Christina Awad, Enhancing the Solar Water Disinfection (SODIS) Method
Using a Fresnel Lens, MS Thesis, University of Californnia Riverside, September 2012.
[9] Mohamed Salah Mahmoudi, Asma Abd El-Sattar Mohamed, Utilization of a
Fresnel Lens Solar Collector in Water Heating for Desalination by Humidification-
Dehumidification Process, Fifteenth International Water Technology Conference,
Alexandria, Egypt, IWTC-15 2011.
[10] G. A. Madhugiri and S. R. Karale, High solar energy concentration with a
Fresnel lens: A Review, International Journal of Modern Engineering Research
(IJMER), Vol.2, Issue.3, May-June 2012, pp-1381-1385.
[11] http://www.nrel.gov/midc/solpos/.
[12] http://aa.usno.navy.mil/data/docs/AltAz.php.
[13] http://rredc.nrel.gov/solar/old_data/nsedb/19912010/hourly/sireonthefly.cgi
[14] COSMOL Multiphysics, Boiling water, Model ID 3972.
37


APPENDIX
Altitude and Azimuth Angles for July 15, 2014
Astronomical Applications Dept.
U.S. Naval Observatory
Washington, DC 20392-5420
BROOMFIELD, COLORADO
W105 06, N39 55
Altitude and Azimuth of the Sun
15-Jul-14
Mountain Daylight Time
Altitude Azimuth
(E of N)
h :m Degree Degree
04:40 -11.0 49.5
04:50 -9.5 51.4
05:00 -8.0 53.2
05:10 -6.4 54.9
05:20 -4.8 56.6
05:30 -3.2 58.3
05:40 -1.6 59.9
05:50 0.6 61.6
06:00 2.1 63.2
38


06:10 3.7 64.7
06:20 5.4 66.3
06:30 7.1 67.8
06:40 8.9 69.3
06:50 10.7 70.8
07:00 12.5 72.3
07:10 14.3 73.7
07:20 16.2 75.2
07:30 18.0 76.7
07:40 19.9 78.1
07:50 21.8 79.6
08:00 23.6 81.1
08:10 25.5 82.5
08:20 27.4 84.0
08:30 29.3 85.6
08:40 31.2 87.1
08:50 33.2 88.6
09:00 35.1 90.2
09:10 37.0 91.9
09:20 38.9 93.5
09:30 40.8 95.3
09:40 42.7 97.1
39


09:50 44.6 98.9
10:00 46.5 100.9
10:10 48.4 102.9
10:20 50.2 105.0
10:30 52.1 107.3
10:40 53.9 109.7
10:50 55.7 112.3
11:00 57.4 115.1
11:10 59.1 118.1
11:20 60.8 121.3
11:30 62.4 124.9
11:40 63.9 128.7
11:50 65.4 133.0
12:00 66.7 137.7
12:10 68.0 142.8
12:20 69.1 148.4
12:30 70.0 154.6
12:40 70.7 161.1
12:50 71.2 168.1
13:00 71.5 175.3
13:10 71.5 182.6
13:20 71.3 189.9
40


13:30 70.8 197.0
13:40 70.2 203.6
13:50 69.3 209.9
14:00 68.3 215.6
14:10 67.1 220.9
14:20 65.8 225.7
14:30 64.4 230.1
14:40 62.8 234.1
14:50 61.3 237.7
15:00 59.6 241.0
15:10 57.9 244.1
15:20 56.2 246.9
15:30 54.4 249.5
15:40 52.6 252.0
15:50 50.7 254.3
16:00 48.9 256.5
16:10 47.0 258.5
16:20 45.1 260.5
16:30 43.2 262.4
16:40 41.3 264.2
16:50 39.4 265.9
17:00 37.5 267.6
41


17:10 35.6 269.3
17:20 33.7 270.9
17:30 31.8 272.4
17:40 29.8 274.0
17:50 27.9 275.5
18:00 26.0 277.0
18:10 24.1 278.5
18:20 22.2 279.9
18:30 20.4 281.4
18:40 18.5 282.9
18:50 16.6 284.3
19:00 14.8 285.8
19:10 13.0 287.3
19:20 11.1 288.7
19:30 9.3 290.2
19:40 7.6 291.7
19:50 5.8 293.2
20:00 4.1 294.8
20:10 2.5 296.3
20:20 0.9 297.9
20:30 -1.2 299.5
20:40 -2.8 301.2
42


20:50 -4.5 302.8
21:00 -6.1 304.5
21:10 -7.6 306.3
21:20 -9.2 308.0
21:30 -10.6 309.9
43


Full Text

PAGE 1

DESIGN AND EVALUATION OF A SELF POSITIONING MECHANICAL SOLAR CONCENTRATOR TO BOIL WATER AND TO PRODUCE WORK by HANG YU B. E ., Xihua University, China, 2012 A thesis submitted to the Faculty of the Graduate School of the University of Colorado Denver in partial fulfillment of the requirements for the degree of Master of Science Mechanical Engineering Program 2014

PAGE 2

ii This thesis for the Master of Science degree by Hang Yu has been approved for the Mechanical Engineering Program b y L. Rafael Sanchez Vega, Chair Marc Ingber Kannan Premnath 7/24/2014

PAGE 3

iii Yu, Hang (MS, Mechanical Engineering) Design and Evaluation of a Self Positioning Mechanical Solar Concentrator to Boil Water and to P roduce Work Thesis directed by Associate P rofessor L. Rafael Sanchez Vega ABSTRACT This work consists of a new design of a solar co ncentrator tailored to two main applications: (i) to boil and produce drinking water; (ii) to evaluate the energy balance done by the system This r esearch includes a design of the tracking system used to focus the solar rays. The tracking sys tem is intended to run unattended and au tomatically tracking the sun exclusively throu gh mechanical means without requiring electric power. The design consists of a Fresnel lens, a moving frame, a track, a retaining mechanism, and a solar collector. The Fresnel lens focuses the solar energy into a circular spot at the collector; The frame holds the collector, keeping it aligned as it rotates with the lens; The track guides the frame keeping it oriented perpendicular to the sun; The solar collector receiv es the sun rays and releases the retaining mechanism, allowing the lens to rotate to the next location. The cycle repeats and the frame tracks the sun along the day This work studies the performance of the solar collector The collector receives the energy of the sun and produces steam by boiling water inside the collector. The pressure build up from the steam can be used to produce work and, after vented to the atmosphere, the steam can be collected as drinking water. The system was evaluated experimentall y and the results may serve as a basis for more comprehensive modeling and optimization to be performed in the future.

PAGE 4

iv The system was designed keeping in mind portability l ow cost, accessib ility simple to maintain and easy to repair. It may be particularly useful to people living in sunny areas with limited electricity and/or drinking water. The form and content of this abstract are appro ved. I recommend its publication. Approved: L. Rafael Sanchez Vega

PAGE 5

v TABLE OF CONTENTS CHAPTER I. INTRODUCTION ................................ ................................ ................................ ........ 1 Purpose of the Study ................................ ................................ ................................ ..... 2 Scope of the Study ................................ ................................ ................................ ........ 2 II. REVIEW OF THE LITERATURE ................................ ................................ .............. 4 III. DESCRIPTION OF THE COMPONENTS OF THE PROPOSED SOLAR TRACKING SYSTEM ................................ ................................ ................................ 6 Fresnel L ens ................................ ................................ ................................ .................. 6 Sun Energy along its Path ................................ ................................ ............................. 9 Solar Collector ................................ ................................ ................................ ............ 1 3 IV. THERMODYNAMIC ANALYSIS OF THE SOLAR CONCENTRATOR ............ 15 V. EXPERIMENTAL EVALUATION OF THE SOLAR CONCENTRATOR ........... 2 2 Amount of H eat A bsorbed by the W ater ................................ ................................ .... 2 2 Quantification of Work Performed ................................ ................................ ............ 23 VI. HEAT TRANSFER APPROACH USING FINITE ELEMENT METHODS ........... 24 Building Geometry ................................ ................................ ................................ ...... 25 Physics Formulation of the Model : Navier Stokes Equation ................................ ... 2 6 Heat Equation ................................ ................................ ................................ .............. 2 7 Initial Values and Boundary Conditions ................................ ................................ ..... 2 8 Heat Transfer with Phase Change ................................ ................................ ............... 2 8 Mesh and Study Type ................................ ................................ ................................ 2 9 FEM Results ................................ ................................ ................................ ................ 30

PAGE 6

vi Limitations of the FEM M odel ................................ ................................ ................... 33 VII. CONCLUSIONS ................................ ................................ ................................ ......... 3 5 REFERENCES ................................ ................................ ................................ .................. 3 7 APPENDIX ................................ ................................ ................................ ........................ 3 8

PAGE 7

vii L IST OF TABLES TABLE 1. Material Properties of Fresnel Lens ................................ ................................ ............... 9 2. Example of NREL R adiation D ata R epresentative of a S unny D ay at Broomfield, CO. Radia tion from the S un is P erpendicular to the L ens ................................ .................. 1 2 3. Properties of T wo P hase W ater V apor ................................ ................................ ........ 21 4. Summary of the C alculated R esults B ased on the E xperimental P arameters .............. 2 2

PAGE 8

viii LIST OF FIGURES FIGURE 1. Cross S ectional V iew of Fresnel L ens ................................ ................................ ........... 7 2. Fresnel L ens with L ens A rea of 0.83 m 2 and F ocal L ength of 34 inches ...................... 8 3. P ath ................................ ................................ ...................... 10 4. Altitude A ngle for July 15, 2014 ................................ ................................ ................. 10 5. Azimuth Angle for July 15, 2014 ................................ ................................ ................ 11 6. Solar Collector ................................ ................................ ................................ ............. 1 3 7. Closer V iew of the S olar C ollector S ystem ................................ ................................ 1 4 8. 2D S ketch of the S olar C ollector ................................ ................................ ................. 1 5 9. the p v D iagram for T wo P hase W ater ................................ ................................ ........ 1 8 10. Temperature as a F unction of Pressure for T wo P hase W ater ................................ ... 1 9 11. Boiling C urve for W ater at A tmospheric P ressure ................................ ..................... 24 12. FEM COSMSOL Geometry M odel ................................ ................................ ............ 26 13. FEM Mesh of S olar C oncentrator ................................ ................................ ............... 30 14. @ t = 0 s the H eat S ource S tarts H eating the S urface and the C ontact S urface R eaches the T emperature of 1000 ................................ ................................ .......... 31 15. @ t = 375 s the H eat F lux t hrough C onvection C onducts H eat to the F luid .............. 31 16. @ t = 750 s V apor S tarts to G enerate L ocally Nucleate B oiling ............................... 32 17. @ t = 1125 s M ore V apor is G enerated ................................ ................................ ...... 32 18. @ t = 1500 s B oiling B ecomes I ntensive F urther I ncreasing V aporization. This B ehavior is R epresentative of F ilm B oiling ................................ ................................ 33

PAGE 9

1 CHAPTER I INTRODUCTION A low cost, small scale throughput device c apable to concentrate energy from the sun and cap able to track the sun mechanically ( without using electric power ), may satisfy many needs around the world. For instance, it could be used as a solar cooker, as a water boiler, as a disinfectant of medical instruments, etc. It c an be used to improve the conditions of people living in remote or arid areas where clean water may be scarce, or as a clean energy source to help reduce the need for deforestation. It may serve as a tool to survival in emergency cases; as for individuals lost in the wilderness, or lost at sea. Tracking s olar concentrat ors on the market today are ty pically electrically powered through batteries or directly by the electrical grid. They are driven by motors with feedback sensors and controllers. These systems tend to be expensive and when used to produce electricity, economies of scale often require high throughput power. T heir use may be limited to large sunny areas where control and access to the electric power grid may present serious issues S olar panels are commercially available for small scale applications (less than 1 KW ) Nevertheless, the a pproach to solar capturing by the Fresnel lens method proposed here, and those using solar panels present significant differences. T he electrical output from the array of solar cells requires accessories such as batteries and inverters which drive the cost higher for these units. Furthermore, solar panels are of difficult repair i f they malfunction during use. The Fresnel method proposed here is exclusively mechanical, and the very high localized temperatures reached at the focus may b e an advantage over solar panels for some applications. The Fresnel system was designed as a

PAGE 10

2 low cost device with ease of maintaining and repairing using readily available economical mechanical components. This work builds from past work of Dr. Sanchez V ega (Advisor) and Noe Villagrana (MS graduate student) at the ME Dept. University of Colorado Denver [1]. Noe and his advisor, Dr. Sanchez Vega, built the first version of a self tracking solar concentrator based on a Fresnel le ns. The prelimi nary version provided the basis to demonstrate the feasibility of several components of the system. In this work, Dr. Sanchez and his graduate student Hang Y u redesigned and built a second prototype Th e second version included s ignificant improvements and addi tions t o the first version and its analysis is the basis f or this study. Purpose of the S tudy This work consist s of the analysis and experimental study of a solar concentrator c apable of tracking the sun mechanically. The tracking movement is integrated with two main applications: (i) to produce drinkable wat er by boiling, (ii) to estimate the efficiency and the work done by the system during operation. The device is designed for simplicity and portability, of easy repair and accessible. This work is envisioned as an addition to sustainable or clean energy methods. It is intended to serve a large segment of the world population with limited access to electrical energy, or drinking water. Upon successful completion of this project, an array of additional applications could be develope d ; some of them readily, such as solar cooking, autoclaves for medical instrument disinfection, etc. Scope of the Study This study is limited to an approximate analysis of the feasibility of the system, and to an approximate experimental evaluation of the main parameters. The system

PAGE 11

3 receives the sun rays and can reach very h igh temperatures at the focus (in excess of 10 00 The collected solar energy is used to power the mechanical movement of the lens and to produce water vapor T he analysis focuses o n the following items; (i) The efficiency of the system in capturing the sun energy required producing steam as a means to ob tain drinking water, (ii) t he estimat ing of the work produced by the system (iii) t he anal ysis of the movement and repositioning of the frame. The analysis includes an estimate of the heat conduction and convection mechanisms, and the evaluation of the properties of water (pressure, or temperature, specific volume, etc.) at the water vapor phase. The analytical approaches are based on general thermodynamic principles, with inclusion of F inite Element Methods (COSMOL). Experimentally, t he amount of work t ransmit ted by the system wa s measured through the amount of compression of a spring. Pressure wa s monitored using a general purpose pressure gage. Temperature was monitored externally at various locations. The change in volume was determined by measuring the displacement of the piston. The overall assessment of the efficiency of the system was based on the amount of water vaporized or boiled on a full cycle, compared to the amount of sun energy received

PAGE 12

4 CHAPTER II REVIEW OF THE LITERATURE This work is a continuation of Dr. Sanchez Vega and his MS student Noe Villagrana, at the ME Dept. University of Colorado Denver [1]. This preliminary work served to prove the feasibility of several components of the system. Literature abound s about systems designed to capture and use solar energy Xie et Al. wrote an extensive review on the recent developments in solar concentrators. Their review summarizes Fresnel lenses systems and its applications to solar power, hydrogen generation, phot o bio reactors, etc. [ 2 ] Fresnel lenses are among the most popular solar concentrator lenses due to their low mass, lightness, and small thickness [ 3 ] Extensive mechanical, physical and optical properties of Fresnel Lenses are available from Fresnel lens m an ufactures such as 3HLens Co. [ 3 ] and Fresnel Technologies Co. [ 4 ] Yinghao Chu published a review overviewing diffe rent solar energy technologies [ 5 ] He focused on Concentrated Solar Power (CSP) and Photovoltaic Solar Panels (PV) as two of the most mature techno logies. He also included Solar T hermoelectricity S ystems (STA), dye sensitized solar cell (DSPV) and concentrated photovoltaic systems. Sahoo et Al., published an Experimental investigation of convective flow boiling in the absorber t ube of th e linear Fresnel reflector solar thermal system [ 6 ] He presented Linear Fresnel Reflection (LFR) technologies with promising application in solar thermal systems. Yousif A. Abakr, and Lee Yeu Sheu designed a water boiler with a tracking system. Their trac king system was controlled by sensors and electric motors programmed through a main controller [ 7 ]

PAGE 13

5 Christina Awad published a MS thesis on Enhancing the Solar Water Disinfection (SODI S) Method Using a Fresnel Lens [ 8 ] She discussed the parameters regardi ng the solar power necessary for disinfection of medical instruments. M. Mahmoud 1 and A. A.El Sattar Mohamed studied the utilization of a Fresnel Lens in water heating and dehumidification process [ 9 ] They used a Fresnel lens for heating saline water for water purification. G. A. Madhugiri and S. R. Karale wrote a review on High S olar E nergy C once ntration with a Fresnel lens [ 10 ] Their paper was focused on the Solar Energy high temperatures using parabolic solar concentrator, Fresnel lens, Reflecting mat erials and solar tracking. The performance of each concentrator was explained and compared.

PAGE 14

6 CHAPTER III DESCRIPTION OF THE COMPONENTS OF THE PROPOSED SOLAR TRACKING SYSTEM The basic components of the solar concentrating tracking system consist of : (i) an element able t an element capable of absorbing the solar energy while minimizing loses due to reflection and heat transfer ; (iii) a moving frame actuated by the thermal energy captured and capable of f ollow ing In this study, a Fresnel lens is used as a concentrating medium. As the light passes through the lens area, it focuses it a t a circular spot at the collector where light is converted into heat A medium inside the collector capture s the heat and expands as the pressure (and temperature) increase s. At a desired pressure (or temperature) setting, the resultant volumetric expansion results in the releasing of a retaining mechanism, allowing the frame to rotate. The frame holds the len s and the collector together As the frame rotates, the tracking mechanism keeps them aligned perpendicular to the sun at all times Fresnel Lens A Fresnel lens is a lens composed of many minute concentric annular sections that can concentrate th [1] Fres nel Lenses where developed in 1822 by a French physicist named Au gustine Jean Fresnel. By using only the refracting sections of a spherical lens and laying them flat, Fresnel made a flat lens capable of concentrating the solar rays in a fashion similar to a standard spherical lens with significant gains on reduced size and weight (Figure 1)

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7 Figure 1 Cross S ectional V iew of Fresnel L ens There are four types of Fresnel lenses: spot, linear, cylindrical and spherical. Spot and linear lenses are the most commonly used lenses in solar power applications, and a spot Fresnel lens is used in this work. A spot Fresnel lens takes the light from th e sun and concentrates it to a singular point called the focal point. For maximum efficiency, the lens called the focal length (Figure 1). The lens used in this s tudy was made of PMMA ( Polymethyl methacrylate ), also called Acrylic glass This material is widely used for solar gathering applications The lens is circular with a focal length = 880 mm It was delivered cut 1 m by 1 m square. The resulting effective Fresnel lens area was 0.83 m 2 (Figure 2). Focal length Focus

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8 Losses due to light absorption or reflection are small, with 92 % transmittance reported by the manufactures [2]. The general specifications are shown in the Table below Figure 2 Fresnel L ens with L ens A rea of 0.83 m 2 and F ocal L ength of 34 inches

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9 Table 1 : Material Properties of Fresnel Lens Fresnel Lens Material PMMA Acrylic Index of Refraction 1.49 Transmittance 92% Thickness 3 Groove P itch 0.5 Focal L ength/Magnification 880 Tensile Modulu s 325 470 Flexural Modulus 390 470 Hardness M80 M100 (Rockwell) Thermal E xpansion 76 Specific G ravity 1.19 Effect of S unlight none Sun Energy along its Path The path followed by the sun is well known. It is typically given by the Azimuth and the Altitude (or Elevation) angles (Figure 3 ) The Azimuth angle is measured from North following a clockwise direction, and the Altitude is measured from the horizon. Another commonly used angle, the Zenith angle, is the complement to the Altitude angle measured from the vertical. These angles can be calculated using solar position algorithms, such a s those developed by NREL [ 11 ]. However, the sun position data is readily available from USNO [ 12 ] and will be used here.

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10 The data includes the azimuth and the altitude (or elevation) angles at any desired interval within 1 120 minutes at any desired location in the USA. T he sun position data corresponding to July 15, 2014 is shown in the Appendix. Fig ure 3 P ath Figures 4 and 5 show the plot s of the azimuth and the altitude angles corresponding to July 15, 2014. The tracking mechanism was adjusted to position the frame according to these angles. Figure 4 Altitude A ngle for July 15, 2014

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11 Figure 5 Azimuth Angle for July 15, 2014 On average a bout 1400 W/m 2 from the sun r eaches th e top of our atmosphere. Part of that energy is reflected back into space or absorbed by our atmosphere. The Denver, Boulder area, receives around 700 W/m 2 on average. NREL [ 1 3 ] maintains national data bases of the amount of solar radiation received anywhere in the country (see USAF#724699 for Broomfield Boulder). The data bases are very complete. They include experimental and modeled hourly average radiation under sunny and cloudy days. Table 2 shows the experimental data corresponding to 60 min s averages of solar radiation re ceived at the experimental location. Radiation data with the lens perpendicular to the sun (METSTAT Dir) was especially useful to our study. The data shows a typical sunny day, although some atmospheric attenuation (light clouds, humidity, etc.) may show i n the statistical averages. Hours between 9:00 am and 4:00 pm are particularly suitable for sun radiation collection.

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12 Table 2 : Example of NREL R adiation D ata R epresentative of a S unny D ay at Broomfield CO Radiation from the S un is P erpendicular to the L ens MM/DD HH:MM Zenith ( deg ) Azimuth ( deg ) ETRN METSTAT Dir 8/13 6:00 86 74 1076 147 8/13 7:00 76 82.5 1331 566 8/13 8:00 64.6 92 1331 759 8/13 9:00 53.3 102.7 1331 852 8/13 10:00 42.5 115.9 1331 902 8/13 11:00 33.2 134.3 1331 930 8/13 12:00 27 160.8 1331 943 8/13 13:00 26.4 193.2 1331 943 8/13 14:00 31.7 221.3 1331 828 8/13 15:00 40.6 241 1331 531 8/13 16:00 51.2 254.9 1331 749 8/13 17:00 62.5 265.9 1331 634 8/13 18:00 73.9 275.6 1331 562 8/13 19:00 84.9 284.8 1298 140 ETRN : Amount of solar radiation received on a surface normal to the sun at the top of the atmosphere during the 60 minute period ending at the timestamp ( W/m 2 ) METSTAT Dir : Amount of solar radiation received in a collimated beam on a surface normal to the sun during the 60 minute period ending at the timestamp ( W/m 2 )

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13 Solar Collector The solar collector receives the radiation from the sun and convert s it into heat (Fig ur e s 6 7 ). The Fresnel lens itself is not sensitive to small changes on the angle of incidence from the sun [4 ]. However, the collector must be properly positioned (perpendicular to the sun) and shaped to minimize reflection. The visual brightness (reflection) of the collector used here was low enough to be considered satisfactory, but no attempts were made here to optimize its geometry. Fig ure 6. Solar Collector Fresnel Lens Solar Collector

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14 Fig ure 7. Closer V iew of the S olar C ollector S ystem The orientation of the collector, perpendicular to the sun, was located by the tracking mechanism within degree at several specified locations. The concentrated beam of the sun approximately located at the center of the collector at all times during the duration of the experiments. This provided a satisfactory assessment of the tracking mechanism. The system was partially isolated; mainly to avoid wind convective heat loses. As the collector is heated by the concentrated beam of the sun, the pressure and temperature increase. At a measured level, the valve opens to the atmospheric pressure and aggressive boiling occurs, vaporizing a significant amount of water. Solar Collector Vapor O utlet Water I nlet Pressure Dial Isolation

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15 CHAPTER IV THERMODYNAMIC ANALYSIS OF THE SOLAR CONCENTRATOR The model of the solar concentrator is shown in Fig ure 8 The concentrator is tilted by the altitude angle, where the central container receive s the heat perpendicular to the rays of the sun. Initially, the container is complete ly filled with water at ambient temperature. Fig ure 8. 2D S ketch of the S olar C ollector As the heat is absorbed, the water and formed vapor expand against the spring loaded piston. The movement of the piston actuate s the tracking mechanism Also, at a set p iston displacement t he valves open releasing the vapor. The displacement of the piston increases the volume of the container. Since the spring compresses upon displacement of the piston, the spring force and therefore the pressure on the fluid increase. The spring can be adjusted to produce a specified pressure at the displacement

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16 corresponding to the releasing of the vapor. Since the temperature of the water vapor mixture increases with pressure, setting the spring also adjusts the desired final temperature at which the vapor is rele ased. Since the amount of water vapor depends on the final temperature, the vaporization is effectively controlled by the amount of compression of the spring. The input power received by the Fresnel lens is taken from the NREL data base at month, day and hour corresponding to our experimental conditions. For a flat plate located at the focus t he lens is reported to smaller than 1 inch in diameter. However, there is a trade off on the amount of light received and reflected by a flat surface. The geometry of the container at the area of incidence was less reflective, but the focal area was larger. Due to some reflection, the actual focal spot was difficult to calculate accurately. It was visually estimated as a circular section around 1. 5 inch diameter. Under the assumptions above, an example of the estimate of the he at rate produced from the radiation energy of the sun is given as: At August 13, from 10:00 11:00 am, sunny skies, s un energy perpendicular to th e lens at Broomfield CO (Table 2 ) : 902 W/m 2 92% transmittance through the lens with an area = 0.83 m 2 gives: 902 (0.83)(0.92)= 688 W The energy received in one hour is = 688 (3600) = 2476.8 k J/hr

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17 Ideally the energy required to vaporize water at 100 starting from 25 is 2571 k J/ k g Assuming no losses, at this radiation level the time to produce one gallon of water woul d take around 4 hours for a lens this size Estimating a concentrated spot area = 1 .77 in 2 ; The concentration at the focus is ~ times. T his gives a flow rate at the focus of around W Also, This is an upper estimate which does not include the amount of energy reflected by the surface of the container. An experimental estimate for reflection will be proposed below. Part of the heat is absorbed by the container and water (liquid and vapor) and part is absorbed but lost through conductive and convective heat lo sses (container radiation effects are considered small and were neglected): Where Ener gy absorbed by the container Energy absorbed by the water and vapor W = Work done by the system against the spring L osses due to conduction from the container to the frame L os ses due to convection with surrounding air

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18 The energy absorbed by the container can be calculated using the specific heat of each material making part of the container : W here are the mass and th e specific heat T he energy absorbed by the water was calculated from steam tables. The approach is approximate, as those tables we re determined under quasi equilibrium conditions. However, data from stea m tables are considered more accurate than using other models for water vapor, s uch as the ideal gas model, or the Van der Waals models. Of interest in this study are the liquid and liquid vapor regions for water. Only a very limited range of the p v diagram (Fig ure 9 ) will apply here. At the critical poi nt, water pressure is 22.1 MPa (647.4 K ). In contrast, the pressure range used in this study locate d between 0.1 MPa (atmospheric pressure) and 0.2 MPa (120.2 ) Our region of interest will be exclusively in the quality region. Fig ure 9. the p v D iagram for T wo P hase W ater

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19 For a pure substance water vapor in quasi equilibrium, the absolute pressure and temperature are functions of each other; knowing one fully defines the other as shown in Fig ure 10. Fig ure 10. Temperature as a F unction of Pressure for T wo P hase W ater The initial conditions are defined at ambient temperature, atmospheric pressure and with the container full of water. As heat is transferred, the temperature increases for water to reach the saturated liquid curve. Further heating increases the temperature (and pressure) with water becoming a two phase fluid mixture in equilibrium. Let : S pecific volume of the saturated liquid S pecific volume of the saturated vapor M ass in liquid phase M ass in vapor phase 90 95 100 105 110 115 120 125 130 0.1 0.12 0.14 0.16 0.18 0.2 0.22 Pressure ( MPa ) Temperature ( )

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20 S pecific volume for the two phase liquid and vapor phase T otal mass of the two phase mixture The total volume is given by The quality of the mixture, x is given by: Reordering: The force applied to the spring by the system is: Where is the spring constant, = piston displacement = spring preload Monitoring the displacement gives the pressure P at the piston: Pa W here = piston diameter and P = absolute pressure With the absolute pressure (and temperature) known as a function of the displacement, we can find from the steam tables the amount of water vaporiz ing with increasing pressure The amount of heat transferred to the water vapor mixture is given by: Where the internal energy U can be calculated from Table 3

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21 Table 3 : Properties of T wo P hase W ater V apor Specific Volume ( ) Specific Internal Energy ( ) P MPa T, 0.1 99.6 0.001043 1.694 417.3 2506.1 0.12 104.8 0.001047 1.428 439.2 2512.1 0.14 109.3 0.001051 1.237 458.2 2517.3 0.16 113.3 0.001054 1.091 475.2 2521.8 0.18 116.9 0.001058 0.9775 490.5 2525.9 0.2 120.2 0.001061 0.8857 504.5 2529.5 Given the path between the initial and final ( P, v ) state conditions, the work done by the system against the spring can be calculated:

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22 CHAPTER V EXPERIMENTAL EVALU ATION OF THE SOLAR CONCENTRATOR Amount of H eat A bsorbed by the W ater The following data apply to our experiment: Total mass = 0.51 k g Piston diameter = d = 1.125 in = 0.02858 m Piston area = A = 0.994 in 2 = 6.41 5 3 (10) 4 m 2 Spring constant = = 10.0 l bs. /in = 1 750 N/m Free length = 3.61 in = 0.0917 m Initial compressi ve preload =3.07 in =0.078 m ; = 3.61 3.07 = 0.54 in = 0.0137 m Final compression = 2.1 5 in = 0.055 m ; = 3.61 2.15 = 1.46 in = 0.037 m Table 4 : S ummary of the C alculated R esults B ased on the E xperimental P arameters Initial Preloaded Final Absolute Pressure ( MPa ) 1.01 1.39 2.50 Temperature ( ) 100.00 109.01 126.86 Piston Displacement ( m ) 0 1.37 3.67 Spring Force ( N ) 0 23.98 64.23 Total Volume ( ) 5.30 5.39 5.54 Quality x ( ) 0 5 30 Specific Internal Energy of liquid ( kJ/kg ) 418.75 456.97 532.89 Estimates f rom the steam tables data show very small amounts of vaporization are produced as the absolute pressure is increased to 0.25 MPa and the temperature is

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23 raised to about 126.8 .This is also shown by the very small values for quality x meaning that m ost of the heat was absorbed at the liquid phase. Upon opening of the valve, the pressure drops to 1 atmosphere and significant vaporization occurs. The change in Enthalpy at the liquid (close enough to ) drops to 532.9 418.7 = 114.1 k J/ k g The latent energy at 100 is 2257 k J/ k g and the mass evaporated becomes = More water is added and the cycle repeats The net mass e vaporated per cycle is ~ 0.026 k g Around 8 cycles repeat ed in one ho ur, giving ~0.21 k g/hr of distilled water. The ideal estimate in p age 1 6 can be used to estimate the efficiency of the system: Efficiency = Quantification of Work Performed The work performed by the system to the spring upon expansion between the initial and final states can be readily calculated: / cycle W hich is small, but effectively operates the lever mechanism.

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24 CHAPTER V I HEAT TRANSFER APPROACH USING FINITE ELEMENT METHODS The results above were determined assuming that the mixture was in quasi equilibrium. This assumption is challenged by the peculiarities of the actual phenomenon. Boiling is significantly noticeable as soon as the sun beams are focused by the lens on the container. Fig ure 11 shows the boiling curve for water at 0.101MPa (1 a tm ). The figure shows the various heat transfer mechanisms for water, which depend on the h eat intensity and the differences of temperatures between the heat source at the collector spot and the liquid. Fig ure 11. Boiling C urve for W ater at A tmospheric P ressure Our estimate of the heat transfer at the focus given in p age 15 was

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25 ; W hich is high enough for nucleate and film boiling. These two boiling modes are also the most effective, resulting in heat transfer rates high than those in conduction [ 1 4 ] The figure makes obvious that quasi equilibrium (which is the basis for the use of steam tables) is not operative for this case. In fact, the measured amount of water vaporized was significantly larger during experimentation that the one estimated in p age 20 using steam tables. FEM COMSOL was used i n an effo rt to develop a more representative model. Boiling does not happen in a closed container provided that it is in equilibrium. In a non equilibrium case as this the container is intensely heated locally. T he high temperature s generated by the Fresnel lens result in easily noticeable boiling in the container. Building Geometry In the COMSOL model, the Heat Transfer in Fluids module is used to solve this phenomenon. A domain that contains liquid (water) and vapor (steam) materials is set up and the properties of the materials are selected via COMSOL materials library.

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26 Fig ure 12. FEM COSMSOL Geometry M odel Physics Formulation of the Model : Navier Stokes Equation The boiling phenomenon is governed by the Navier Stokes equations. In an inertia frame of reference, the Navier Stokes equations general form is: Where is the flow viscosity, is the fluid density, is the pressure, is the deviatoric component of the total stress tensor, is other body forces (per unit volume) acting on the fluid, is the delta operator. Consider the velocity field and pressure in liquid phase is incompressible, the Navier Stokes equations can be derived (subscript L denotes liquid phase) :

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27 Where is the fluid density is the fluid velocity is the liquid pressure is the altitude angle is the viscosity For vapor phase, the Navier Stokes equations can be solved as compressible substance (subscript L denotes vapor phase): Where is the vapor density is the vapor velocity is the vapor pressure is the altitude angle is the viscosity is the bulk (second) viscosity Heat Equation In general, 3 D heat equation is described as

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28 Where is the specific heat capacity is the thermal conductivity Because the temperature at t he liquid and vapor interface is at saturation temperature, the heat equation can be solved by the vapor phase Navier Stokes equations: Where is the specific heat capacity is the thermal conductivity of the vapor Initial Values and Boundary Conditions The initial values of this model are set as all boundaries have the room temperature and the heat source has a temperature of acting on the copper cup (a copper penny at the focus melts easily) which is designed to stand the high temperature and conduct heat flux to the water. All other boundaries are set as insulated. Heat Transfer with Phase Change In this model, the phase change is between liquid water and vapor, and the parameters can be calculated by the parameters of two different phases as:

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29 Where is the specific heat capacity is the thermal conductivity is the fluid density is the quality of the mixture is the latent heat distribution ; is the Heaviside function is the Dirac pulse, is the latent heat. The two phases in this model are corresponding to liquid (water) phase and vapor (steam) phase, which can be found in the material library. Mesh and Study Type In this model, a finer, physical controlled mesh is used to conduct the Finite Elem ent Analysis calculation. There are 532 DOFs (plus 103 internal DOFs) to be solved in this model. In order to show the transient process, a Time Dependent study type should be selected to compute.

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30 Fig ure 13. FEM Mesh of S olar C oncentrator FEM Result s The figure bellow s show the evolution of the trans ient temperature distribution, and the 2 D transient phase change

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31 Fig ure 14. @ t = 0 s the H eat S ource S tarts H eating the S urface and the C ontact S urface R eaches the T emperature of 1000 Fig ure 15 @ t = 375 s the H eat F lux t hrough C onvection C onducts H eat to the F luid

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32 Fig ure 16 @ t = 750 s V apor S tarts to G enerate L ocally Nucleate B oiling Fig ure 17 @ t = 1125 s M ore V apor is G enerated

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33 Fig ure 18 @ t = 1500 s B oiling B ecomes I ntensive F urther I ncreasing V aporization. This B ehavior is R epresentative of F ilm B oiling The FEM results show that the system produce s significant steam before open ing to the atmosphere. As long as the container is exposed to the s un, vapor is generated T he pressure inside the container will be raised for as long as the vaporization is increased. After the piston moves to a set distance, opening the valve to the atmosphere the boiling p oint decrease s to 100 and aggressive vapor ization is observed. Limitation s of the FEM M odel This model is based on several assumptions: 1) The reflection caused by the copper surface has not been considered in this model, which results in the solar energy loss and decrease in temperature applied to the surface. 2) The model is solved in a 2D plane instead of a 3D model, which results in an inaccurate quantitative outcome. Only qualitative conclusions can be

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34 summarized from this model. 3) The radiation and convection from the other hot sides of surface to the liquid are neglected, which also enhance the vaporizati on to form and produce vapor. Despite the limitations above, th is study shows a need to take into account the non equilibrium progression for this heat transfer case.

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35 CHAPTER VI I CONCLUSIONS 1. The prototype of the Fresnel lens system demonstrated its feasibility on water boiling applications. Although the efficiency of the current prototype (at around 21.8%) was rather low this number has the potential for improvement through better isolation and better design. 2. Modeling of the water boiling phenomenon was readily accomplished using steam tables. However, the assumption of quasi equilibrium required for these tables was shown to depart from more sophisticated FEM modeling as well as from experimental observations. 3. The amount of vaporization ( 0.21 k g/hr distilled water) estimated by steam tables was relatively low Although this estimate may be low, or more efficient, better isolated systems can be implemented, this issue can also be addressed simply by increasing the size of the Fresnel lens. Since the throughput increase to the square of the length, an increase of 50% in length would more than double t he area of the lens. The use of square lenses, as opposed to the circular pattern used here, will also increase throughput for the same frame size. 4. The tracking mechanism located the lens perpendicular to the sun for the tracking range used. The lever syst em, enacted by the movement of the piston, could be adjusted to fit this intended application. The transition from water to vapor, with the corresponding increase of pressure under heat was a convenient method t o actuate the lever system

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36 5. The lens generates extremely high temperatures (in excess of 1000 ) at the focus. These high temperatures can be used in other applications, for instance, in the design of Autoclaves to disinfect medical instruments, to increase t he throughput of solar panels, etc. Other research areas of interest may include accelerated fermentation through the application of heat to certain kinds of flora for production of electricity, waste disposal through high level temperature incinerators, e tc.

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37 REFERENCES [1] Noe Villagana (Advisor: L. Rafael Sanchez Vega) Master of Science Project Thesis Mechanical Engineering, College of Engineering, University of Colorado Denver, Denver, CO., August 2013. [2] W.T. Xie et Al., Concentrated solar energy applications using Fresnel lenses : A review Elsevier, Renewable and Sustainable Energy Reviews 15 (2011) 2588 2606 [3] www.BHLens.com [4] www.fresneltech.com [5] Yinghao Chu, Review and Comparison of Different Solar Energy Technologies Global Energy Network Institute (GENI) August 2011 [6] Sahoo et Al., Experimental investigation of convective flow boiling in the absorbertube of the linear Fresnel reflector solar thermal system Solaris 2012 India, Varanasi, India 7 9 Feb 2012 [7] Yousif A. Abakr, Lee Yeu Sheu, Solar Water Boiler with Tracking Syste m s College Subang Jaya, Malaysia [8] MS Thesis University of Californnia Riverside September 2012. [9] Mohamed Salah Mahmoud1, Asma Abd El Sattar Mohamed, Utilization of a Fresnel Lens Solar Collector in Water Heating for Desalination by Humidification Dehumidification Process Fifteenth International Water Technology Conference, Alexandria, Egypt IWTC 15 2011 [10] G. A. Madhugiri and S. R. Karale, High solar energy concentration with a Fresnel lens: A Review International Journal of Modern Engineering Research (IJMER), Vol.2, Issue.3 May June 2012 pp 1381 1385 [11] http://www.nrel.gov/midc/solpos/ [12] http://aa.usno.navy.mil/data/docs/AltAz.php [13] http://rredc.nrel.gov/solar/old_data/nsedb/19912010/hourly/sireonthefly.cgi [14] COSMOL Multiphysics l ID 3972

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38 APPENDIX A ltitude and A zimuth A ngles for July 15, 2014 Astronomical Applications Dept. U.S. Naval Observatory Washington, DC 20392 5420 BROOMFIELD, COLORADO W105 06 o N39 55 o Altitude and Azimuth of the Sun 15 Jul 14 Mountain Daylight Time Altitude Azimuth (E of N) h :m Deg ree Deg ree 04:40 11.0 49.5 04:50 9.5 51.4 05:00 8.0 53.2 05:10 6.4 54.9 05:20 4.8 56.6 05:30 3.2 58.3 05:40 1.6 59.9 05:50 0.6 61.6 06:00 2.1 63.2

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39 06:10 3.7 64.7 06:20 5.4 66.3 06:30 7.1 67.8 06:40 8.9 69.3 06:50 10.7 70.8 07:00 12.5 72.3 07:10 14.3 73.7 07:20 16.2 75.2 07:30 18.0 76.7 07:40 19.9 78.1 07:50 21.8 79.6 08:00 23.6 81.1 08:10 25.5 82.5 08:20 27.4 84.0 08:30 29.3 85.6 08:40 31.2 87.1 08:50 33.2 88.6 09:00 35.1 90.2 09:10 37.0 91.9 09:20 38.9 93.5 09:30 40.8 95.3 09:40 42.7 97.1

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40 09:50 44.6 98.9 10:00 46.5 100.9 10:10 48.4 102.9 10:20 50.2 105.0 10:30 52.1 107.3 10:40 53.9 109.7 10:50 55.7 112.3 11:00 57.4 115.1 11:10 59.1 118.1 11:20 60.8 121.3 11:30 62.4 124.9 11:40 63.9 128.7 11:50 65.4 133.0 12:00 66.7 137.7 12:10 68.0 142.8 12:20 69.1 148.4 12:30 70.0 154.6 12:40 70.7 161.1 12:50 71.2 168.1 13:00 71.5 175.3 13:10 71.5 182.6 13:20 71.3 189.9

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41 13:30 70.8 197.0 13:40 70.2 203.6 13:50 69.3 209.9 14:00 68.3 215.6 14:10 67.1 220.9 14:20 65.8 225.7 14:30 64.4 230.1 14:40 62.8 234.1 14:50 61.3 237.7 15:00 59.6 241.0 15:10 57.9 244.1 15:20 56.2 246.9 15:30 54.4 249.5 15:40 52.6 252.0 15:50 50.7 254.3 16:00 48.9 256.5 16:10 47.0 258.5 16:20 45.1 260.5 16:30 43.2 262.4 16:40 41.3 264.2 16:50 39.4 265.9 17:00 37.5 267.6

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42 17:10 35.6 269.3 17:20 33.7 270.9 17:30 31.8 272.4 17:40 29.8 274.0 17:50 27.9 275.5 18:00 26.0 277.0 18:10 24.1 278.5 18:20 22.2 279.9 18:30 20.4 281.4 18:40 18.5 282.9 18:50 16.6 284.3 19:00 14.8 285.8 19:10 13.0 287.3 19:20 11.1 288.7 19:30 9.3 290.2 19:40 7.6 291.7 19:50 5.8 293.2 20:00 4.1 294.8 20:10 2.5 296.3 20:20 0.9 297.9 20:30 1.2 299.5 20:40 2.8 301.2

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43 20:50 4.5 302.8 21:00 6.1 304.5 21:10 7.6 306.3 21:20 9.2 308.0 21:30 10.6 309.9