COMPUTATIONAL AND EXPERIMENTAL...
Transcript of COMPUTATIONAL AND EXPERIMENTAL...
COMPUTATIONAL AND EXPERIMENTAL STUDIES ON A SOLAR CHIMNEY POWER PLANT
by
Sandeep Kumar Patel
A thesis submitted in fulfillment of the
requirements for the degree of
Master of Science in Engineering
Copyright © 2013 by Sandeep Kumar Patel
School of Engineering and Physics
Faculty of Science, Technology, and Environment
The University of the South Pacific
June 2013
i
Declaration of Originality Statement by Author
I, Sandeep Kumar Patel, hereby declare that the write up of the research project is
purely my own work without the inclusion of any other research materials that has
already been published or written. Any individuals’ work or idea that has been
included within the report has been clearly referenced and credit given to the person.
_________________
Sandeep Kumar Patel
S11031673
28/06/2013
Statement by Supervisor
I hereby confirm that the work contained in this supervised research project is the
work of Sandeep Kumar Patel unless otherwise stated.
____________________
Dr. M. Rafiuddin Ahmed
Principal Supervisor
28/06/2013
ii
Acknowledgements
First of all, I would like to thank the almighty God for giving me the
knowledge and patience to successfully finish this research. I would like to thank my
parents, Jayanti Lal Patel and Gitaben Patel, my sister, Nikita Ben Patel and my
wife, Varsha Mala for their continuous encouragement throughout the project. I
would also like to thank my uncle and aunty and my cousins for their continuous
support through the project. I sincerely thank my supervisor, Dr. M. Rafiuddin
Ahmed, for his guidance, assistance and support in my experiments, publications,
and compilation of the thesis.
I am very grateful to the University of the South Pacific, Faculty of Science
and Technology Research Committee for funding this research project. I also owe
gratitude to all the academic and technical staff members of the School of
Engineering and Physics; special thanks to Mr. Sanjay Singh and Mr. Shiu Dayal for
their guidance in technical issues and helping me with the fabrication.
I would also like to record my thanks to my colleagues Mr. Krishnil Ram,
Mr. Shivneel Prasad, Mr. Vineet Chandra, Mr. Deepak Prasad, Mr. Sandeep Reddy,
Mr. Kaushik Sharma, Mr. Epeli Naboloniwaqa, Mr. Jai Goundar, Mr. Mohammed
Faizal, Mr. Mohammed Tazil, Mr. Ronit Singh, Mr. Imran Jannif, and Mr. Shahil
Ram for helping me with the experiments and giving moral support.
I would further like to thank all those who have helped me in anyway to
accomplish my Masters Degree, a big milestone in my life.
iii
Publications
1. Patel, S. P., Prasad, D. and Ahmed, M. R., “Computational Studies on the Effect
of Geometric Parameters on the Performance of a Solar Chimney Power Plant”,
Energy Conversion and Management, Elsevier, (Under review).
2. Patel, S. P. and Ahmed, M. R., “Computational and Experimental Studies on a
Solar Chimney Power Plant for Power Generation in Pacific Island Countries”,
manuscript under preparation.
iv
Abstract
The solar chimney power plant (SCPP) is a renewable-energy power plant that
transforms solar energy into electricity. The SCPP consists of three essential
elements – solar air collector, chimney tower, and wind turbine(s). The present work
is aimed at optimizing the geometry of the major components of the SCPP using a
computational fluid dynamics (CFD) software ANSYS-CFX to study and improve
the flow characteristics inside the SCPP. The overall chimney height and the
collector diameter of the SCPP were kept constant at 10 m and 8 m respectively. The
collector inlet opening was varied from 0.05 m to 0.2 m. The collector outlet height
was also varied from 0.5 m to 1 m. The collector outlet diameter was also varied
from 0.6 m to 1 m. These modified collectors were tested with chimneys of different
divergence angles (0 – 3 ) and also different chimney inlet openings of 0.6 m to 1 m.
The diameter of the chimney was also varied from 0.25 m to 0.3 m. Based on the
CFD results, the best configuration was achieved using the chimney with a
divergence angle of 2 and chimney diameter of 0.25 m together with the collector
opening of 0.05 m and collector outlet diameter of 1 m. Based on the best
configuration obtained from the 10 m SCPP, a scaled down model of 1:2.5 was
modelled and simulated. The 4 m SCPP had a fixed chimney height of 4 m and a
collector diameter of 3.2 m. The collector outlet height was also kept constant at 0.2
m. the collector outlet diameter was varied from 0.24 m to 0.4 m and the chimney
throat diameter was varied from 0.10 m to 0.12 m. The collector opening was also
varied from 0.02 m to 0.08 m. This configuration was then fabricated and tested. PT
– 100 temperature sensors were used to measure temperature across the collector and
along the chimney. A pitot static tube was used to measure the dynamic pressure at
the throat. The dynamic pressure was converted into velocity. The experimental
results were then compared to the 4 m CFD results. The results were very similar. A
100 m SCPP was later modelled and simulated to predict the power available for
bigger size towers. The 100 m tower produced a maximum available power of 35.8
kW and maximum air velocity of 22.72 m/s. Such a plant will be suitable to meet the
power requirements of small islands in Pacific Island Countries where the
requirements are of the order of tens of kilowatts.
v
Table of Contents
Declaration of Originality i
Acknowledgements ......................................................................................................... ii
Publications ................................................................................................................... iii
Abstract ......................................................................................................................... iv
1. Introduction .............................................................................................................. 1
1.1 Thesis Objectives ...................................................................................................... …2
1.2 Thesis Outline.............................................................................................................. 2
2. Literature Review ...................................................................................................... 4
2.1 History......................................................................................................................... 4
2.2 Solar Chimney Power Plant ......................................................................................... 5
2.3 Components ................................................................................................................. 6
2.3.1 Collector .............................................................................................................. 6
2.3.2 Chimney .............................................................................................................. 8
2.3.3 Turbines ............................................................................................................... 9
2.4 Thermodynamics Cycle ............................................................................................. 10
2.4.1 The Solar Chimney Power Plant as a Gas Turbine .............................................. 11
2.4.2 Air Standard Analysis of Solar Gas Turbine Cycle ............................................. 12
2.4.3 Air Standard Analysis of a Solar Chimney Power Plant Cycle ............................ 14
2.5 Solar Chimney Power Plant Theoretical and Experimental Models ............................. 18
3. Methodology ........................................................................................................... 26
3.1 Numerical Work ........................................................................................................ 26
3.1.1 CFD Code .......................................................................................................... 26
3.1.2 Full Buoyancy Model (Density Difference) ........................................................ 28
3.1.3 Boussinesq Model .............................................................................................. 29
3.1.4 Numerical Setup................................................................................................. 29
3.1.5 Geometry Generation or Modelling .................................................................... 30
3.1.6 Mesh or Grid Generation .................................................................................... 31
3.1.7 Physics Pre – Processor ...................................................................................... 33
3.1.8 Solver ................................................................................................................ 34
vi
3.1.9 Post – processor ................................................................................................. 35
3.2 Experimental Method................................................................................................. 35
3.2.1 Chimney Bellmouth ........................................................................................... 36
3.2.2 Solar Air Collector ............................................................................................. 40
3.2.3 Solar Chimney ................................................................................................... 43
3.2.4 Foundation ......................................................................................................... 43
3.2.5 The 4m Tall Experimental SCPP ........................................................................ 46
3.2.6 PT – 100 Temperature Sensor ............................................................................ 47
3.2.7 DaqPRO Datalogger........................................................................................... 48
3.2.8 Pitot – Static Tube .............................................................................................. 51
3.2.9 Furness Controls Digital Micromanometer FCO510 ........................................... 51
4. Results and Discussions .......................................................................................... 54
4.1 Numerical Results for the 10m SCPP ......................................................................... 54
4.2 Numerical and Experimental Results for the 4 m Tall SCPP ...................................... 69
4.3 The 100m SCPP Numerical Results ........................................................................... 79
5. Conclusions ............................................................................................................ 83
6. References .............................................................................................................. 84
vii
List of Figures
Figure 1.1: Rate of the world energy use growth [2] ............................................................ 1
Figure 2.1: The SCPP in Manzanares, Spain [11] ................................................................ 4
Figure 2.2: The SCPP collector [19] .................................................................................... 7
Figure 2.3: Schematic of an SCPP collector [20] ................................................................. 8
Figure 2.4: The chimney of the SCPP [24]........................................................................... 9
Figure 2.5: The axial flow type turbine for SCPP [26] ....................................................... 10
Figure 2.6: The T-s diagram for a solar gas turbine cycle ................................................... 12
Figure 2.7: Schematic of an SCPP ..................................................................................... 14
Figure 2.8: The T-s diagram for an SCPP cycle ................................................................. 15
Figure 3.1: Structure of ANSYS CFX................................................................................ 30
Figure 3.2: The SCPP model created in Autodesk Inventor ................................................ 31
Figure 3.3: The solar chimney mesh .................................................................................. 32
Figure 3.4: The solar air collector mesh ............................................................................. 32
Figure 3.5: Various boundaries of the SCPP ...................................................................... 34
Figure 3.6: Schematic of the 4m tall experimental SCPP ................................................... 36
Figure 3.7: The 3D view and the schematic of the chimney bellmouth ............................... 37
Figure 3.8: The flanges for the chimney bellmouth ............................................................ 37
Figure 3.9: Flat bars being bent and welded to the flange ................................................... 38
Figure 3.10: Flat bars and triangular pieces of sheet metal being welded together .............. 38
Figure 3.11: The chimney bellmouth being machined in the lathe to level the inside surface
......................................................................................................................................... 39
Figure 3.12: The chimney bellmouth fully welded together ............................................... 39
Figure 3.13: The 3D view and the schematic of the frames of the solar air collector ........... 40
Figure 3.14: Frames for the solar air collector .................................................................... 41
Figure 3.15: Perspex for the solar air collector ................................................................... 42
Figure 3.16: The solar air collector pre-allignment............................................................. 42
Figure 3.17: A section of a solar chimney .......................................................................... 43
Figure 3.18: Schematic of the SCPP foundation and footing details ................................... 44
Figure 3.19: The solar chimney foundation ........................................................................ 44
viii
Figure 3.20: Cement being poured onto the SCPP foundation ............................................ 45
Figure 3.21: Wire mesh 665 on top of the ground surface before cement is poured ............ 45
Figure 3.22: The solar air collector sitting on the black painted cement absorber................ 46
Figure 3.23: The 4m tall experimental SCPP ..................................................................... 47
Figure 3.24: PT – 100 Temperature sensor [66] ................................................................. 48
Figure 3.25: The DaqPro datalogger [67] ........................................................................... 49
Figure 3.26: A Pitot – Static tube ....................................................................................... 51
Figure 3.27: Furness Controls Digital Micromanometer..................................................... 52
Figure 4.1: Schematic diagram of the SCPP with the various parameters that were studied 54
Figure 4.2: Power available for case 5 for various collector inlet openings and various
chimney divergence angles. ............................................................................................... 56
Figure 4.3: Temperature contours on the collector for collector inlet opening of 0.05 m ..... 57
Figure 4.4: Temperature contours on the collector for a collector inlet opening of 0.2 m .... 57
Figure 4.5: Power available for cases 1, 5 and 9 for the collector inlet openings of 0.1 m and
different chimney divergence angles.................................................................................. 59
Figure 4.6: Power available for cases 3, 7 and 11 for the collector inlet openings of 0.1 m
and different chimney divergence angles ........................................................................... 60
Figure 4.7: Power available for cases 1, 3, 5, 7, 9 and 11 for the collector inlet opening of 0.1
m and different chimney divergence angles ....................................................................... 60
Figure 4.8: Power available for cases 2, 6 and 10 for the collector inlet opening of 0.1 m and
different chimney divergence angles.................................................................................. 61
Figure 4.9: Power available for cases 1, 2, 5, 6, 9 and 10 for the collector inlet opening of 0.1
m and different chimney divergence angles ....................................................................... 62
Figure 4.10: Velocity vectors on the entire SCPP for case 3 for the collector inlet opening of
0.05 m and chimney divergence angle of 2⁰ ....................................................................... 63
Figure 4.11: Temperature contours on the entire SCPP for case 3 for the collector inlet
opening of 0.05 m and chimney divergence angle of 2⁰ ..................................................... 63
Figure 4.12: Temperature variation along the chimney height for case 3 for the collector inlet
opening of 0.05 m and chimney divergence angle of 2⁰ ..................................................... 64
Figure 4.13: Velocity variation along the chimney height for case 3 for the collector inlet
opening of 0.05 m and chimney divergence angle of 2⁰ ..................................................... 65
ix
Figure 4.14: Temperature variation along the outer radius of the collector to the center
measured at 0.025 m above ground for case 3 for the collector inlet opening of 0.05 m and
chimney divergence angle of 2⁰ ......................................................................................... 66
Figure 4.15: Temperature variation from the ground to the collector outlet at the center for
case 3 for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰ .......... 67
Figure 4.16: Velocity variation from the ground to the collector outlet at the center for case 3
for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰ .................... 67
Figure 4.17: Temperature variation from the ground to the top of the chimney for case 3 for
the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰.......................... 68
Figure 4.18: Velocity variation from the ground to the top of the chimney for case 3 for the
collector inlet opening of 0.05 m and chimney divergence angle of 2⁰ ............................... 68
Figure 4.19: Temperature and pressure sensors measurement locations .............................. 70
Figure 4.20: Power available for cases A, B, C and D for the chimney divergence angle of 2
and different collector inlet openings ................................................................................. 71
Figure 4.21: Mass flow rate for cases A, B, C and D for the chimney divergence angle of 2
and different collector inlet openings ................................................................................. 72
Figure 4.22: Velocity for cases A, B, C and D for the chimney divergence angle of 2 and
different collector inlet openings ....................................................................................... 73
Figure 4.23: Velocity vectors on the entire SCPP for case D for the collector inlet opening of
0.04 m ............................................................................................................................... 74
Figure 4.24: Temperature contours on the entire SCPP for case D for the collector inlet
opening of 0.04 m ............................................................................................................. 75
Figure 4.25: Temperature variation along the outer radius of the collector to the center
measured at various locations for both experimental and CFD for case D for the collector
inlet opening of 0.04 m ..................................................................................................... 76
Figure 4.26: Temperature variation along the chimney height for both experimental and CFD
for case D for the collector inlet opening of 0.04 m ........................................................... 77
Figure 4.27: Temperature variation across the collector from 9:00 am to 8:00 pm on a typical
day .................................................................................................................................... 78
Figure 4.28: Temperature variation along the chimney from 9:00 am to 8:00 pm on a typical
day .................................................................................................................................... 79
Figure 4.29: Temperature variation from the ground to the top of the chimney for the 100 m
SCPP ................................................................................................................................ 80
Figure 4. 30: Velocity variation from the ground to the top of the chimney for the 100 m
SCPP ................................................................................................................................ 81
x
Figure 4.31: Temperature variation along the outer radius of the collector to the center
measured at 0.025 m for the 100 m SCPP .......................................................................... 82
xi
List of Tables
Table 3. 1: PT – 100 Temperature Sensor Specifications ........................................ 48
Table 3. 2: DaqPRO Datalogger Specifications ...................................................... 49
Table 3. 3: Furness Controls Digital Micromanometer Specifications .................... 52
Table 4. 1: Different Configurations of the 10 m SCPP Tested ............................... 55
Table 4. 2: Different Configurations of the 4 m SCPP Tested ................................. 69
xii
Nomenclature
Symbol Descriptions Units
A Cross-sectional area m2
Compression temperature ratio -
Specific heat capacity J / kg K
Grashoff number -
Acceleration due to gravity m / s2
Enthalpy J / kg
Mass flow rate kg / s
n Power law profile exponent -
P Power W
Prandtl number -
Pressure Pa
Rayleigh number -
Reynolds number -
Cycle pressure ratio -
S Source term -
s Entropy J / kg
T Temperature K
Time s
Vector of velocity in XYZ coordinates m / s
xiii
Velocity Magnitude m / s
v Velocity m / s
Height (or vertical distance) m
Greek Symbol Descriptions
Thermal expansion coefficient 1 / K
γ Specific heat ratio of air -
Efficiency -
ρ Density kg / m3
Stress tensor -
Thermal Conductivity W / m K
Subscripts
1 Solar gas turbine compressor inlet
1’ Solar chimney atmospheric inlet
2 Solar collector inlet
3te Turbine exit
4 Chimney exit
E Energy equations
lift Power required to lift air in the chimney
M Momentum equations
ref Reference
xiv
shaft Shaft power
tot Total
Superscripts
* Normalized quantity
‘ Solar chimney atmospheric inlet
Abbreviations
CFD Computational fluid dynamics
SCPP Solar chimney power plant
1
1. Introduction
The increase in global energy consumption and the rapid development of global
economy is known to cause serious environmental problems [1]. Compared to the
past years, the demand for electricity today is far greater than ever in both developed
and developing countries. Even today, fossil fuels are the primary fuel sources and
are still widely used for major electricity generation as shown in Figure 1.1 [2].
Many developing countries cannot afford these energy sources due to its high cost,
and nuclear power stations are an unacceptable risk in many locations around the
world. Inadequate energy supplied do not only lead to higher energy costs, but
poverty as well which commonly results in population explosions [3]. Not only are
they expensive and cause harm to the environment, fossil fuels are diminishing day
by day. With fossil energy nearing exhaustion as well as greenhouse effect and air
pollution being more severe, utilization of renewable energy technologies are
increasingly gaining great importance and is playing a major role in solving the
above problems in future [4].
Figure 1.1: Rate of the world energy use growth [2]
2
Although renewable energy related technologies are still at its primary stages, they
hold a great promise for the future. This is due to the fact that renewable energy is a
cleaner and greener source of energy and is also available in abundance. While there
are so many different sources of renewable energy, solar energy is one of the more
promising ones since the sun is the ultimate source of most renewable energy
supplies. Although solar energy has the highest available energy, only a little fraction
of the available energy is used [5]. The biggest problem with solar energy is that it is
only available in the day, but technical advancements through research has made it
possible to harness the solar energy at night by storing the solar energy available in
the day.
Although there are so many devices that have been built to harness this energy from
the sun, majority of them are very expensive to build and maintain and that is a
major issue in developing countries. The solar energy device must be simple, reliable
and cheap to build and maintain. The solar chimney power plant (SCPP) meets these
conditions very well. The solar chimney is simple and reliable since it doesn’t have
many moving parts and it is cheap since the raw materials needed to build the solar
chimney are readily available in most developing countries. The SCPP can also
produce power at night by using water bags inside the collector to store and release
heat slowly at night to provide a continuous 24 hours power supply.
1.1 Thesis Objectives
� To perform a detailed literature survey on an SCPP, their operational concepts,
the individual components, and overall performance parameters.
� To fully design an SCPP using Autodesk Inventor and test it numerically using a
commercial code ANSYS CFX.
� To fabricate and install an SCPP at the University of the South Pacific (USP).
� To experimentally determine the performance of the SCPP under various
operational conditions.
� To simulate a 100 m tall SCPP and predict the power available.
1.2 Thesis Outline
� Chapter 1 gives a general introduction on the importance of renewable energy
and how an SCPP will help dealing with the problem the world is facing.
3
� Chapter 2 gives an overview of the development and studies carried out on the
SCPP over years. Also major components of the SCPP are discussed in details.
Detailed theoretical analysis using the thermodynamic cycle is also presented in
this chapter.
� Chapter 3 provides a detailed methodology of both numerical and experimental
works of the SCPP.
� Chapter 4 presents the numerical and experimental results of the SCPP.
� Chapter 5 finally summarizes the main findings of this research.
4
2. Literature Review
2.1 History
In 1903, Isidoro Cabaynes, a Spanish artillery colonel gave one of the earliest
descriptions about the solar chimney power plant. His idea of the solar chimney
power plant was attaching some kind of wind propeller to the chimney of a house for
power generation [6].
In 1926, Prof Engineer Bernard Dubos proposed a construction of a solar chimney
power plant whose chimney will be positioned on the slope of a high mountain. In
1931, a German author, Hanns Gunther demonstrated the concept of a solar chimney
power plant technology by performing a small experiment based on plate and a spirit
lamp which acts as the heat from the Sahara desert and the small wind wheel on top
of the chimney represents the wind turbines [6, 7].
The first real concept of the solar chimney power plant was proposed by Professor
Jorg Schlaich in 1978. In 1982, a 50kW solar chimney power plant was constructed
and tested out in Manzanares, Spain [8, 9] as shown in Figure 2.1.
Figure 2.1: The SCPP in Manzanares, Spain [11]
5
The prototype had collector radius of 122m and a chimney height of 194.6m and
produced a maximum updraft air velocity of 15m/s under no load conditions [7]. The
prototype was tested for 7 years till 1989 where the tower collapsed due to rust and
storm winds affecting the guy wires which were not protected against rust [10].
2.2 Solar Chimney Power Plant
Solar thermal power plants are normally classified into two main categories: high
and low temperature power plants. This mainly depends on their temperature level.
High temperature power plants collect direct solar radiation and often use a closed
cycle thermodynamic process. These plants have very high efficiency but also high
capital costs and operational costs. Solar chimney power plants are classified as low
temperature power plant since its working fluid is kept primarily in the free
atmosphere [12]. Solar chimney power plants comprise of three major components
[13]:
� The collector (greenhouse)
� The chimney
� The power conversion unit which included turbines
The chimney is a long cylindrical structure placed in the centre of the circular
greenhouse collector [14, 15]. The turbine is normally placed at the base of the
chimney where the pressure difference is large from the outside [8]. The green house
collector is made out of transparent glass or plastic film which is supported close to
the ground and its height increases towards the centre where the chimney is placed.
The solar radiation enters the greenhouse collector and gets absorbed by the soil. The
air around the soil gets heated up and starts to rise towards the chimney where a
turbine is placed to produce power. Suction from the chimney draws more hot
buoyant air from the collector and cold air from free atmosphere replaces the hot air
through natural convection. To ensure that the solar chimney power plant works at
night, water filled tubes/bags are placed under the collector roof [16].
The solar energy is first converted into thermal energy by the soil, which is then
converted into kinetic energy by the hot air and later converted into mechanical
energy by the turbine rotors which is then eventually converted into electrical energy
[15].
6
Solar chimney power plants have notable advantages compared to other solar
thermal power plants [3]:
� The collector uses both direct and diffuse solar radiation. This is very important
for tropical countries where the sky is often overcast.
� Solar chimney power plants can operate for 24 hours with the help of water filled
tubes placed under the collector roof. During the day the soil and water filled
tubes absorb heat from solar radiation and at night the water filled tubes releases
heat slowly.
� Solar chimney power plants are very reliable and are not likely to break down
since it has very few moving parts. The structure is very robust and the only
moving part is the turbines thus require very little maintenance.
� Solar chimney power plants do not need cooling water like other conventional
power plants. This is an advantage since majority of the sunny countries have
difficulty getting fresh drinking water.
� Solar chimney power plants can even be built in less developed countries since
building materials mainly concrete and glass or plastic sheets are readily
available in sufficient quantities. Also solar chimney power plants do not need
high – tech manufacturing plants for construction and this will help less develop
countries with more job opportunities.
One of the most notable disadvantage of solar chimney power plants is poor or low
efficiency level due to solar chimney power plants converting a very little amount of
solar radiation into electricity, thus requiring a much larger collector area [3, 17].
2.3 Components
2.3.1 Collector
The collector of a solar chimney power plant is normally made up of glass or plastic
film which is stretched horizontally for several meters above ground as shown in
Figure 2.2. The height of the collector gradually increases towards the centre where
the chimney is often placed. This ensures smooth transition of hot air flowing from
the collector to the chimney, therefore reducing frictional and eddy losses. The main
purpose of the collector is to allow the transmission of short wave radiation and
blocks the long wave radiation emitted by the heated ground. This will result in the
7
heating up of air under the collector which then flows radially towards the centre
where the chimney is positioned [15, 18].
Figure 2.2: The SCPP collector [19]
The soil under the collector acts like a thermal storage for solar radiation and slowly
emits most of it during the day and some at night. The soil itself is not enough to
emit radiation throughout the night for continuous 24 hours power generation. For
continuous 24 hours operation, water filled black tubes are often placed side by side
on the soil under the collector as shown in Figure 2.3. The water filled tubes absorb
solar radiation in the day and slowly emits it at night. This is because thermal storage
of water works more efficiently than soil alone since the specific heat capacity of
water is about five times larger than that of soil and even at low water velocities –
from natural convection in tubes – the heat transfer between water tubes and water is
much more efficient than that between ground surface and soil layers underneath.
These water filled tubes are only filled once and are sealed to prevent evaporation
from taking place [16, 18, 20]. These water filled tubes are transparent on the upper
surface to allow solar radiation through and are painted black at the bottom surface
to absorb most of the solar radiation [20]. The volume of water in the tube
8
corresponds to the water layer thickness and this is selected to achieve desired power
output characteristics.
Figure 2.3: Schematic of an SCPP collector [20]
2.3.2 Chimney
The solar chimney or tower of a solar chimney power plant is a long cylindrical
structure placed at the centre of the collector and one or more turbo generators are
installed at its base for the purpose of power generation [8, 14, 15, 21, 22] as shown
in Figure 2.4. The solar chimneys normally have a specific angle of inclination, often
vertical as it is easier to build and operate [23].
The solar chimney itself is the actual thermal engine of the solar chimney power
plant. The solar chimney is like a pressure tube with low frictional losses due to its
favourable surface – volume ratio [15, 18, 20]. The updraft air velocity or the mass
flow rate of the updraft air is approximately proportional to the air temperature rise
in the collector and the solar chimney or tower height [18, 20].
9
Figure 2.4: The chimney of the SCPP [24]
2.3.3 Turbines
The turbine (or turbines) is one of the core components of solar chimney power
plants. The main purpose of the turbine is to convert the kinetic energy of heated air
into mechanical energy using the turbine rotors [20]. The conventional turbine of a
solar chimney power plant is normally placed at the base of the chimney because of
easier installation and maintenance for large scale solar chimney power plants [20].
The turbine of solar chimney power plant is usually an axial flow type turbine as
shown in Figure 2.5. The characteristics of these turbines (the number of rotor
blades, specific speeds, and turbine diameters) lie between that of a wind turbine and
a gas turbine. It has more than two to three blades of wind turbine but not as many as
gas turbines. The pitch angle of the blades can be adjusted like wind turbines but due
to the flow being enclosed in a solar chimney power plant like a gas turbine, the
turbine may have radial inflow guide vanes [20, 25]. Due to the fact that the turbines
do not work with staged velocity like free – running wind energy converters, but as
shrouded pressure – staged wind turbo generators, the specific power output is
roughly one order of magnitude higher than that of a velocity staged wind turbine.
The air velocity before and turbine is approximately the same [18]. The power output
10
achieved is proportional to the product of volume flow per unit time or the volume
flow rate and the pressure difference or pressure drop across the turbine [15, 18].
Figure 2.5: The axial flow type turbine for SCPP [26]
2.4 Thermodynamics Cycle
The thermodynamic processes in a solar chimney power plant could be presented as
a simple thermodynamic cycle obtained from the air standard cycle to give a clear
and useful understanding of the real cycles that they simulate. The working fluid in a
solar chimney power plant is air and it is assumed to behave as an ideal gas [27].
Assumptions for air standard cycle analysis
� The working fluid is dry air assumed to be behaving as an ideal gas with constant
specific heat
� The mass flow rate of the system is constant
� The compression and expansion processes in the air standard cycle are adiabatic
and reversible (isentropic)
� The change in kinetic energy of the air between inlet and exit of each component
is negligible
11
� In the combustor and passages, there are no stagnation pressure drops
� The inlet and exit atmospheric conditions are identical
� The only heat flow is the net heat flow of air in the system
2.4.1 The Solar Chimney Power Plant as a Gas Turbine
The first observation made for a solar chimney power plant cycle is that it is
ultimately a gas turbine (Joule or Brayton) cycle. Considering the gas turbine air
standard cycle, there are normally four processes involved; isentropic compression,
constant pressure heat addition, isentropic expansion and constant pressure heat
removal [27].
Although the solar chimney power plant cycle and the gas turbine cycle are basically
the same, there are some practical differences. One of the main practical differences
is that the inlet and the exit atmospheric conditions are assumed to be identical in the
gas turbine cycle, however this is not true for the solar chimney power plant cycle
since the exhaust is at the altitude of the chimney top, and the atmosphere has the
additional function of recompressing the exhaust air to the ground inlet conditions
[27]. This compression doesn’t have to be isentropic; it can be approximated by a
polytropic expression of the form:
(1)
where p is the pressure, ρ is the density and n is some exponent that is not
necessarily equal to the specific heat ratio γ.
In order to study and understand the solar chimney power plant cycle, it is very
important to simulate the solar chimney power plant cycle by a gas turbine air cycle
where the chimney is eliminated and an isentropic compressor is added. To better
simulate the environmental conditions of the solar chimney power plant, we assume
that the gas turbine plant is placed at the altitude of the chimney top. The pressure
ratio chosen for the solar chimney power plant is the ratio of the atmospheric
pressure on the ground level to the atmospheric pressure at the solar chimney top.
Now, the pressure ratio for the gas turbine and the solar chimney power plant is
equal. However, this gas turbine solar concept have other practical drawbacks such
12
as the collector pressure being higher than the local atmospheric pressure at the top
of the chimney and the large amount of power to be transmitted between the turbine
and the compressor. The low temperature solar gas turbine cycle will however serve
a useful bench mark for the solar chimney cycle.
2.4.2 Air Standard Analysis of Solar Gas Turbine Cycle The T-s diagram for a solar gas turbine cycle is shown in Figure 2.6. The T-s
diagram represents the different processes in the cycle. The analysis for the solar gas
turbine cycle is taken from Cohen et al. [28] and Archer and Saarlas [29] which were
later derived by von Backstrom and Gannon [27] to simplify the equations.
Figure 2.6: The T-s diagram for a solar gas turbine cycle
The cycle pressure ratio is defined as:
(2)
The compression temperature ratio is defined as:
(3)
13
The cycle efficiency is defined as the turbine shaft power out divided by the thermal
power or the solar energy transferred to the air moving across the solar the solar
collector:
(4)
The turbine output power or the shaft power out is defined as:
(5)
The thermal power or solar energy transferred to the air in the collector is defined as:
(6)
The cycle efficiency can be rewritten as:
(7)
The above equation clearly shows that the plant cycle efficiency is only a function of
cycle pressure ratio, r and not the cycle temperature ratio, t13 which is defined below.
The cycle temperature ratio can be defined as:
(8)
where is the compressor inlet temperature, is the temperature rise in the
combustor and is the compressor exit temperature.
The specific power normalised with T1 is defined as:
(9)
From the above equation, it can be said that the specific power depends on both
cycle pressure ratio and collector temperature rise.
14
2.4.3 Air Standard Analysis of a Solar Chimney Power Plant Cycle
The analysis of a solar chimney power plant cycle is very similar to that of a gas
turbine. One of the main differences is that the compression process does not take
place in the system but in the environment when the air starts to descend. The other
difference is that any analysis of compression inlet temperature at the top altitude
will be avoided since this is a variable temperature determined by a point that
intersects between the constant cooling pressure line from point 4 and the polytropic
(not isentropic) compression line from point 2. A much better reference temperature
is since it is the ground level temperature and can be easily measured. The
temperature will be made use of and is defined as the intersection between the
constant pressure line through point 4 and the isentropic line through point 2.
In an ideal gas turbine cycle where there are no irreversible processes, all the power
can be extracted from the flow by an ideal turbine as it expands from collector exit
pressure, to the chimney exit pressure, to obtain the shaft power .
For a solar chimney, the power required to lift the air up the chimney should also be
considered. The schematic and T-s diagram of an SCPP is shown in Figure 2.7 and
Figure 2.8 respectively.
Figure 2.7: Schematic of an SCPP
15
Figure 2.8: The T-s diagram for an SCPP cycle
The total power available is defined as:
(10)
The power required to lift the air up the chimney is defined as:
(11)
There is no heat transfer or shaft work in this section of the chimney.
The enthalpy change in the chimney is defined as:
(12)
Following from the assumption of zero friction and heat transfer, the energy
exchange is isentropic. The value of can be equated to the amount of air that has
descended again in the atmosphere after having been cooled to .
16
The amount of enthalpy gained is defined as:
(13)
The turbine output power or the shaft power out is now defined as:
(14)
The cycle efficiency is defined as:
(15)
The thermal power transferred to the air in the collector is defined as:
(16)
In the solar chimney cycle, the pressure ratio is defined in terms of the chimney exit
and the collector exit pressures:
(17)
The temperature ratio is now defined as:
(18)
The solar chimney efficiency or the cycle efficiency is now the same as for the gas
turbine and is defined as:
(19)
Equating the temperature drop with the potential energy,
(20)
The solar chimney efficiency is now defined as:
(21)
17
As seen in the above equations, the cycle efficiency of an idea solar chimney plant is
directly proportional to the chimney height, and inversely proportional to the
collector inlet temperature.
To calculate the specific power, the cycle temperature ratio is defined as:
(22)
For the solar chimney cycle, the specific power is normalized to the collector inlet
temperature :
(23)
Using equation (23) and the following expression,
(24)
The specific power can now be written as:
(25)
The equations above clearly show that the specific power is proportional to the
chimney height and the collector temperature rise, and inversely proportional to the
collector inlet temperature.
18
2.5 Solar Chimney Power Plant Theoretical and Experimental Models The very first theoretical model for the solar chimney power plant was developed by
Mullet [30] who presented an analysis and derived its overall efficiency. In his study
he concluded that solar chimney power plants have very low overall efficiencies and
it is vital for power generation in large scale. Based on the data and results from the
Manzanares tower prototype, Padki and Sherif [31] extrapolated solar chimney
power plants model for medium – to – large scale power generations. In their studies
they investigated the effect of various geometrical configurations on the chimney
performance and efficiency. A detailed study was undertaken by Pasumarthi and
Sherif [15] to investigate the performance characteristics of a solar chimney power
plant both theoretically and experimentally. They presented a mathematical model
which was used to study effect of various geometric parameters on the air
temperature, air velocity, and power output of the solar chimney power plant. In the
further studies conducted by Pasumarthi and Sherif [32], experimental modifications
were conducted on the collector. The modifications were extension of the collector
base and an introduction of an immediate absorber. According to them, both the
changes help in increasing air temperature and mass flow rate inside the chimney
resulting in higher power output. They also conducted a brief economic analysis on
solar chimney power plants.
The first attempt to solve a solar chimney power plant simulation by Computational
Fluid Dynamics (CFD) was made by Bernades et al. [33]. They presented numerical
analysis of natural convection in a radial solar heater operating in steady state to
predict the thermo-hydrodynamic behaviour of the device. A Finite Volume Method
in Generalized Coordinates was used to analyse the Navier-Stokes and Energy
Equations allowing a detailed visualization of the effects of geometric of optimal
geometric operational characteristics. According to results obtained by Bernades et
al. [33], curved junctions initiates well distributed-temperature fields, recirculation-
free flow as well a higher mass flows compare to straight junctions at the centre of
the base of the collector.
An analysis of the driving potential of a solar chimney power plant was presented by
Kroger and Blaine [34]. Several theoretical models were assessed and the influences
of prevailing ambient conditions were evaluated. Kroger and Blaine presented in
19
their studies that humidified air can enhance the driving potential and at certain
conditions condensation may occur.
A study including chimney friction, system, turbine and exit energy losses was
introduced by Gannon and von Backstrom [35]. For this study, a simple collector is
used to the mass flow rate and the temperature rise in the solar collector. A simple
solar chimney power plant model was fabricated and was used to compare with the
simulation. From their study, it can be concluded that the pressure drop associated
with vertical acceleration of air is about three times the pressure drop associated with
friction and also for flared chimney; the vertical pressure drop can be eliminated.
Gannon and von Backstrom [36] later proposed a turbine design based on the
requirements of a solar chimney power plant whereby the turbine was integrated
with the chimney. This was done by radially offsetting the chimney base legs so that
they can act as inlet guide vanes which will introduce pre-whirl before the rotor
reducing the exit kinetic energy. In their studies, they optimized the blades using a
surface vortex method to achieve blades of minimum chord and low drag. They
concluded from their study that their proposed turbine design can extract over 80%
of the power available in the flow. Further studies by Gannon and Backstrom [37,
38] revealed that their experimental turbine has a total-to-total efficiency of 85-90%
and total-to-static efficiency of 77-80% over the design range.
A comprehensive analytical and numerical model describing the performance of
solar chimney power plants was developed by Bernades et al. [13]. The model was
used to estimate the power output of solar chimney power plants and also to study
the effect of several ambient conditions and structural dimensions on the power
output. The results from the mathematical model were validated with the
experimental results which were then used to predict the performance characteristics
of large-scale solar chimney power plants. It can be concluded from their results that
the chimney height, the factor of pressure drop across turbine, the diameter and the
optical properties of the collector are important parameters for solar chimney power
plant design.
The effects of atmospheric winds on the performance of solar chimney power plants
were presented by Serag – Eldin [39] using a computational model. The
20
computational model comprises of governing partial differential equations
expressing conservation of mass, energy and balance of momentum and also a two
equation model of turbulence to study the flow pattern of a small-scale solar
chimney power plant in the neighbourhood. The results show that the effect of
atmospheric winds on solar chimney power plants cannot be ignored and also there
is a total degradation of the solar chimney power plant performance due to strong
winds and substantial degradation even with slow winds unless the collector inlet
height is kept significantly low.
A study based on the loss coefficient and mean exit swirl angle of the flow in the
collector-to-chimney transition region as dependent on inlet guide vanes (IGV)
stagger angle and the collector roof height was presented by Kirstein and von
Backstrom [40]. Their experiments were conducted on a small scale solar chimney
power plant and later tested with a commercial CFD code. It was found that there
was a very good agreement between the two results in terms of predicting the flow
angles, velocity components, and internal and wall static pressures. Semi-empirical
equations were also developed later to predict the loss coefficient and the turbine
mean inlet flow angles as dependent on the collector deck height and the inlet guide
vane setting angle for solar chimney power plants.
A more comprehensive model was developed by Tingzhen et al. [41] to evaluate the
performance of solar chimney power plants by investigating various parameters like
the relative static pressure, driving force, power output and efficiency. Numerical
studies were also performed to explore the geometric modifications on the system
performance based on the Manzanares prototype as an example and it shows a
reasonable agreement with the analytical model.
Pretorius and Kroger [22] evaluated the influence of a recently developed convective
heat transfer equation, a more accurate turbine inlet loss coefficient, quality collector
roof glass and various types of soil on the performance of a large-scale solar
chimney power plant. Results from his studies indicated that the new heat transfer
equation reduces the power output of the solar chimney power plant significantly.
Also, the effect of a more accurate turbine inlet loss coefficient is very minor and by
using a better quality glass can vastly improve the efficiency of the solar chimney
21
power plant. Models tested with Limestone and Sandstone soil produced virtually
comparable results to a Granite-based model. In another study performed by
Pretorius and Kroger [42], they claimed that 24hrs power production is possible and
plant power production is a function of the collector roof shape and collector inlet
height.
A study was conducted by von Backstrom and Fluri [43] to investigate analytically
the validity and applicability of the assumption that, for maximum fluid power, the
optimum ratio of the turbine pressure drop to pressure potential (available system
pressure difference) is 2/3. From their analysis and an analysis conducted by
Schlaich, both these analyses predicted that the maximum fluid power is available at
much lower flow rate and much higher turbine pressure drop than predicted by the
constant pressure potential assumption. It can be concluded from their study that the
constant pressure potential assumption may well lead to overestimating the size of
the flow passages in the plant, and designing a turbine with poor stall margin and
very high runaway speed margin.
The effect of tower area change in a solar chimney power plant was studied by
Koonsrisuk and Chitsomboon [44] using CFD technology. The results from their
study showed that the tower area change affects the efficiency and the mass flow rate
through the plant. It was found out from their study that although velocity increases
at the top of a convergent tower, the mass flow rate remains similar as that of a
constant area tower. For a divergent tower design, velocity increases near the base of
the chimney and the maximum kinetic energy also occurs at the base of the chimney.
Ninic [12] determined the dependence of the work potential on the hot air flowing
inside the collector, the air humidity and the atmospheric pressure as a function of
elevation. In his study, several collector types were analysed using dry and humid
air. Also, the effects of several chimney heights on the air work potential were
found.
The effects of solar radiation on the flow inside the solar chimney plant was
analysed by Huang et al. [45]. In their study, the Boussinesq model and the Discrete
Ordinate Model (DO) were employed and simulations were carried out. It can be
concluded from their study that the pressure throughout the system is negative, the
22
temperature difference between the collector inlet and collector outlet and the
differential pressure in the collector-chimney transition section increases with
increasing solar radiation intensity.
The use of dimensionless variables was proposed by Koonsrisuk and Chitsomboon
[46] to study the flow in a small-scale solar chimney power plant. Water and air were
chosen as working fluids for the modelling study and Computational Fluid Dynamics
(CFD) was used to obtained results. From the CFD results, air proved to be a better
working fluid for a small-scale solar chimney power plant. Also from CFD results, it
was shown that the models were dynamically similar to the prototype.
A study of a new mathematical model was developed by Wei et al. [47] and it was
based on the concept of relative static pressure. According to the authors, optimizing
local geometric dimensions between the collector outlet and the chimney inlet can
lead to an increase in local velocity, a more uniform temperature profile and a drop
in relative static pressure; thus, improving the energy conversion and reducing the
energy losses.
A sensitivity analysis on the influence of the quality, thickness, reflectance,
emissivity, shape, and insulation of the collector roof glass, the cross section of the
collector roof supports, various ground types, ground surface roughness, absorptivity
and emissivity, turbine inlet and bracing wheel loss coefficients, and the ambient
pressure and lapse rate on the performance of a large-scale (reference) solar chimney
power plant was presented by Pretorius and Kroger [48]. Results from computer
simulations indicated that collector roof insulation, emissivity and reflectance, the
ambient lapse rate, and ground absorptivity and emissivity all have a vital effect
on the power production of a solar chimney power plant.
Zhou et al. [7] conducted an experimental study of temperature field on a pilot size
SCPP. In their study, the temperature distribution across the collector at different
heights and the temperature along the chimney were measured. According to their
study, it was found that temperature inversion is produced when the solar radiation
increases from minimum and clears up when the absorber bed is heated to a high
temperature. Further studies were conducted by Zhou et al. [49] by comparing the
experimental results to a simulated study obtained form a developed mathematical
23
model. Very close correlation between the two results makes it possible to use a
mathematical model to predict the performance of an SCPP of a different scale.
Numerical simulations evaluating characteristics of heat transfer and air flow in the
solar chimney power plant with an energy storage layer including the solar radiation
and the heat storage on the ground was carried out by Tingzhen et al. [50]. It can be
concluded from their study that the ground heat storage depends on the solar
radiation incidence and also higher temperature gradients leads to more energy loss
from the ground [6].
Further studies were conducted by Koonsrisuk and Chitsomboon [51] based on the
use of dimensional analysis together with engineering intuition to combine eight
variables into a single dimensionless variable to establish dynamic similarity
between a prototype and scaled models of a solar chimney power plant. They tested
three plant configurations numerically for similarity; fully geometrically similar,
partially geometrically similar, and dissimilar types. From their studies, it was found
out that the value obtained from the physical plant through testing was almost the
same as that of numerical simulations and this provides the validity of the
proposition. Also from their studies, it was found that for a fixed solar heat flux,
different-sized models that are partially or fully geometrically alike share an equal
excess temperature across the outlet of the collector roof.
A study based on improving the flow of air in the solar chimney power plant was
undertaken by Klarin et al. [52]. They carried out basic geometry changes in a solar
chimney power plant by analysing it using CFD in a three dimensional domain. They
design various shapes for the inside and also outside of the solar chimney power
plant and tested them.
Ming et al. [53] performed further studies on the thermal performance of a solar
chimney power plant. They established a simple analysis of the air flowing through
the solar chimney power plant and also a thermodynamic cycle of the solar chimney
power plant including the environment. They also produced mathematical model of
ideal and actual cycle efficiencies for medium-sized and later for large-sized solar
chimney power plant. The results from their work posed as a theoretical guideline for
designing and building a commercial-size solar chimney power plant in China.
24
Hamdan [14, 54] performed an analytical model and a thermodynamic study of
steady airflow inside a solar chimney. He used a simplified Bernoullis equation
combined with fluid dynamics and ideal gas equation using EES solver to predict the
performance of the solar chimney power plant. The analytical model was validated
against an experimental and numerical data available and was also used to evaluate
the effect of geometric parameters on the solar chimney power plant. From his
analysis, it could be said that the height and diameter of the solar chimney are the
most important variables for solar chimney power plant design and also the collector
area has small effect on second-law efficiency but strong effect on harvested energy.
Further studies were conducted by Hamdan [55] to evaluate the use of constant
density assumption and compare it with the more realistic chimney mathematical
model. From the results obtained, it can be concluded that the constant density
assumption simplifies the analytical model but it over predicts the power output. It
can also be concluded that maximum power output depends on the turbine head.
A more detailed numerical analysis of a solar chimney power plant was conducted
by Sangi et al. [56]. They created a mathematical model based on the Navier-Stokes,
continuity and energy equations to study the solar chimney power plant in detail. The
mathematical model created together with CFD software FLUENT were used to
study the temperature, velocity and pressure distributions in a solar chimney power
plant. The results produced were then validated with the experimental data from the
Manzanares solar chimney power plant.
An experimental investigation based on the effects of different climate on the
efficiency of a pilot size SCPP was conducted by Kasaeian et al. [57]. According to
their study, temperature inversion was observed at the bottom of the chimney after
sunrise on both hot and cold days. It was observed in their experimental study that
maximum velocity was obtained inside the chimney while the velocity at the
collector entrance or collector opening was zero.
A numerical analysis on the influence of ambient crosswind on the performance of
an SCPP was conducted by Ming et al. [58]. The results obtained showed that
ambient crosswind has a positive and a negative effect on the performance of an
SCPP. When the ambient crosswind is weak, the flow field is deteriorated and the
25
output power reduces. When the ambient crosswind is strong enough, the mass flow
rate increases, thus the output power also increases. This increase in mass flowrates
results from a wind suction effect on top of the chimney caused by the high velocity
wind (Bernoulli principle). Further numerical analysis were conducted by Ming et al.
[59] to overcome the negative effect of strong ambient crosswind by employing a
blockage a few meters away from the collector inlet opening. According to their
study, negative effects resulting from strong ambient crosswinds have been greatly
overcome by a large extent with the help of these blockages.
Li et al. [60] proposed a theoretical model to study the effects of collector radius and
chimney height on the power output of an SCPP with turbines. The theoretical model
was validated with the experimental data of the Manzanares SCPP. According to
their study, there is a limitation on the maximum collector radius as the power output
of the SCPP increases very slowly beyond that maximum radius. On the other hand,
the chimney height has no limitation at present due to the current construction
technology and also the highest chimney size investigated in the literature is only
1500 m.
Bernades and Zhou [61] analysed the sensible heat storage physical process in an
SCPP collector and also the use of water bags as heat storage. Thicknesses of water
bags were varied and simulated with and without insulations. From the results
obtained, it can be concluded that thicker water bags reduces the daily temperature
efficiently and the thermal stratification effect.
26
3. Methodology
3.1 Numerical Work
3.1.1 CFD Code
The rapid development in computer technology nowadays has forced the use of
numerical methods, for example, computational fluid dynamics (CFD) to be used in
research and experiments. CFD provides a cheaper and an accurate solution to
research problems. ANSYS CFX Version 14 was used for simulation purpose in this
research project. ANSYS CFX Version 14 uses unsteady Navier-Stokes equation in
their conservation form to solve set of equations. The instantaneous equation of mass
(continuity), momentum, and energy conservation are presented below [62].
The Continuity Equation
(26)
The Momentum Equations
(27)
where the stress tensor, , is related to the strain rate by
(28)
The Total Energy Equation
(29)
where is the total entahlpy, related to the static enthalpy h(T, p) by:
(30)
27
The term represents the work due to viscous stresses and is called the
viscous work term. This models the internal heating by viscosity in the fluid, and is
negligible in most flows.
The term represents the work due to external momentum sources and is
currently neglected.
In this research project, the flow of air inside the SCPP was due to natural
convection. CFX Version 14 can model natural and mixed convection flows by the
inclusion of buoyancy source terms. Natural convection flows occurs when the
convection of a fluid is driven only by local density variations while mixed
convection flows occurs when the convection of a fluid is driven by both a pressure
gradient and buoyancy forces [63].
Buoyancy is normally driven by variations in density and this can arise from a
number of sources. Some of the sources are:
� Variations in local temperature causing change in density; this is natural
convection.
� Variations in the mass fraction cause density variations because each
component usually has a different density. This occurs in multicomponent
flows.
� The difference in density between the phases in multiphase flows, including
particle transport modelling results in a buoyancy force.
� For a General Fluid, if density is variable (that is, defined by an expression),
a buoyancy force will arise.
� Local pressure variations also cause changes in density in case of ideal gases
and real fluids. These changes are often small and the buoyancy effect is
usually not important in the flow. Buoyancy does not necessarily need to be
modelled if there are no other sources of buoyancy.
Temperature variations which causes buoyancy forces in a mixed convection flow
can be estimated by using the ratio of Grashoff and Reynolds Numbers,
28
(31)
where is the thermal expansion coefficient. A value approaching or exceeding
unity indicates that buoyancy effects are significant in the flow, while small values
indicate that buoyancy effects can be ignored or are insignificant.
In purely natural convection problems, the Rayleigh Number (Ra) indicates the
relative strength of the buoyancy induced flow and is given by:
(32)
where Pr is the fluid Prandtl number. The laminar flow regime is generally
characterized by Ra < 108, while turbulent buoyant flow is characterized by Ra >
1010.
For buoyancy calculations, the gravity vector components in x, y and z must be set.
These are interpreted in the coordinate frame for the domain. Buoyancy effects can
be simulated using one of two available models in CFX:
� Full Buoyancy Model (Density Difference)
� Boussinesq Model
3.1.2 Full Buoyancy Model (Density Difference)
For single phase flows, this model is used when temperature and pressure variations
directly affects the fluid density. These include all ideal gases and real fluids and
when a multicomponent fluid is used. For Eulerian multiphase or particle tracking, it
is also set even if all phases have constant density. In most gases, temperature
variations significantly affect densities. A buoyancy reference temperature must be
specified as an approximate average value of the expected domain density. For
multiphase simulations, other factors must be considered [63].
For buoyancy calculations involving variable density, is evaluated directly.
This option is set automatically when the simulation involves multiphase flow,
multicomponent flow, or a fluid having density set as a function of temperature,
pressure, or other field variables.
29
3.1.3 Boussinesq Model
For many applications involving buoyancy, when the change in density over the
expected range of conditions is relatively small, it is assumed to have a constant fluid
density. This is often true for many liquids. The Boussinesq model is employed
when the fluid density is not a function of temperature or pressure [63].
Although, the Boussinesq model uses a constant density fluid model, a local
gravitational body force is applied throughout the fluid that is a linear function of
fluid thermal expansivity, and the local temperature difference with reference to a
datum called the buoyancy reference temperature. A reference temperature should be
specified as an approximate average value of the expected domain temperature.
In the Boussinesq model, a constant reference density is used for all terms other
than the buoyancy source term. The buoyancy source term is approximated as:
(33)
where is the thermal expansivity:
(34)
and is the buoyancy reference temperature.
3.1.4 Numerical Setup
The CFD work in this project was carried out using a commercial CFD software
known as ANSYS CFX. For the CFD simulation in ANSYS CFX, many processes
are involved and listed in Figure 3.1.
30
Figure 3.1: Structure of ANSYS CFX
The processes above will be discussed later in detail.
3.1.5 Geometry Generation or Modelling
The SCPP model was created using Autodesk Inventor software as shown in Figure
3.2. The SCPP model consisted of two major components, the solar chimney and the
solar collector. The solar chimney and the solar air collector were modelled
separately for ease of meshing. The model was created on the x-y plane and was
revolved around the z-axis to obtain the three-dimensional model. All dimensions are
in millimetres (mm) unless specified. The overall height of the SCPP was 10 m and
the solar air collector was 8m in diameter. A divergence orientated collector design
was used due its superior performance compared to a parallel orientated and a
convergence orientated collector design [64]. A straight chimney design and
divergence designed were both used for this project.
Geometry Generation Software (Autodesk Inventor)
Mesh Generation Software (ANSYS ICEM CFD)
ANSYS CFX - Pre (Physics Pre - processor)
ANSYS CFX - Solver (Solver)
ANSYS CFD - Post (Post - processor)
31
Figure 3.2: The SCPP model created in Autodesk Inventor
3.1.6 Mesh or Grid Generation
ANSYS ICEM CFD software was used for grid generation. The computational
domain was discretized using the ICEM CFD Hexa-mesher or user-defined meshing
method. The hexahedral grid used ensures that the results obtained are of the highest
quality and accuracy. Meshing for the solar chimney and solar air collector are
shown in Figure 3.3 and Figure 3.4. The total number of nodes for the model was
157432.
32
Figure 3.3: The solar chimney mesh
Figure 3.4: The solar air collector mesh
33
3.1.7 Physics Pre – Processor
The CFD work in this study was carried out using ANSYS CFX. ANSYS CFX is a
Reynolds Averaged Navier-Stokes Equation (RANSE) solver based on finite volume
technique. For the simulations, steady state analysis was chosen. The computational
domain was divided into two which consisted of the solar chimney and the solar air
collector. The working fluid used was air which was modelled as an ideal gas. The
entire model was built from the origin and extended in the positive y direction. The
buoyancy model was then activated by specifying the gravity of –g in the y direction
which represented real life flow. The reference pressure used was 1 atm. The heat
transfer model selected for the current simulation was total energy. This option was
chosen because change in kinetic energy is of significant importance in addition to
the changes in temperature. The boundary type at the inlet was opening with
boundary conditions of zero relative pressure and a static temperature of 303 K. The
boundary type at the outlet was also set as opening with a relative pressure of zero
and a static temperature of 303 K since the temperature at the height of 10 m does
not differ too much compared to the ground air temperature. The ground was
assigned a boundary type of wall with no-slip condition activated. The temperature
of the ground was set as 323 K. The remaining sides of the computational domain
were modelled as wall with no-slip condition. The no-slip condition ensures that the
fluid moving over the solid surfaces does not have a velocity relative to the surfaces
at the point of contact. Finally, appropriate interface region was created between the
chimney and the solar air collector. Automatic mesh connection method was selected
for the interface. All these boundary conditions are set for ideal conditions. The
simulation was run for 5000 iterations; for convergence, residual type of RMS and
the residual target value of 1 x 10-7 were set as the criteria. Figure 3.5 shows the
boundaries for the SCPP.
34
Figure 3.5: Various boundaries of the SCPP
3.1.8 Solver
The component that solves the CFD problem is called the Solver (ANSYS CFX –
Solver). The required results are produced in a non-interactive/batch process. In
ANSYS CFX Version 14, the CFD problem is solved as follows [65]:
1. The partial differential equations are integrated over all the control volumes
in the region of interest. This is the same as applying a basic conservation
law to each control volume.
2. These integral equations are converted to a system of algebraic equations by
generating a set of approximations for the terms in the integral equations.
3. The algebraic equations are solved iteratively.
Solving the equations iteratively is necessary because of the nonlinear nature of the
equations. As the solution approaches the exact solution, it is said to converge. For
each iteration, an error, or residual, is reported as a measure of the overall
conservation of the flow properties.
To determine how close the final solution is to the exact solution depends on a
number of factors. These factors include the size and shape of the control volumes
35
and the size of the final residuals. The solution process requires no user interaction
and is, therefore, usually carried out as a batch process.
The solver produces a results file that is then passed to the post-processor.
3.1.9 Post – processor
The post-processor (ANSYS CFD – Post) is the component used to analyze,
visualize and present the results interactively. ANSYS CFD – Post is a flexible,
state-of-the-art post – processor that is designed to allow easy visualization and
quantitative analysis of the CFD simulations results. Post-processing includes
anything from obtaining point values to complex animated sequences [65].
Examples of some important features of post-processors are:
� Visualization of the geometry and control volumes
� Vector plots showing the direction and magnitude of the flow
� Visualization of the variation of scalar variables through the domain
� Quantitative numerical calculations
� Animation
� Charts showing graphical plots of variables
� Hardcopy and online output.
3.2 Experimental Method
A 4 m tall SCPP was constructed for experimental purpose. The overall dimensions
of the SCPP are shown below in Figure 3.6. The components of the SCPP were
fabricated individually in-house.
36
Figure 3.6: Schematic of the 4m tall experimental SCPP
3.2.1 Chimney Bellmouth
The chimney bellmouth is a very important parameter in the design of an SCPP. The
bellmouth shape acts as a nozzle which allows the air to accelerate through to the
turbine section of the SCPP. The chimney bellmouth was the first component to be
fabricated. The schematic of the chimney bellmouth is shown in Figure 3.7.
37
Figure 3.7: The 3D view and the schematic of the chimney bellmouth
A large mild steel (MS) sheet metal plate 12mm in thickness was cut off in a shape
of a circle to provide the flanges for the chimney bellmouth and the foundation as
shown in Figure 3.8. The outer diameter of the flanges was 700 mm.
Figure 3.8: The flanges for the chimney bellmouth
A 10 mm MS flat bar was cut and bent to match the profile of the inner radius of the
chimney bellmouth as shown in Figure 3.9. The inner radius of the chimney
bellmouth was 200 mm.
38
Figure 3.9: Flat bars being bent and welded to the flange
Triangular pieces were also cut of from the 12mm MS sheet metal to fill in the gaps
as shown in Figure 3.10. A 3.2 mm diameter welding rod was then used to fill up all
the gaps between the flat bar and the triangular sheet metal pieces.
Figure 3.10: Flat bars and triangular pieces of sheet metal being welded together
The bellmouth was fitted into the lathe to smoothen and level the inside surface as
shown in Figure 3.11. A cardboard with the profile of the inner radius of the
39
chimney bellmouth drawn into it was used as a guide to exactly match the chimney
bellmouth in the lathe.
Figure 3.11: The chimney bellmouth being machined in the lathe to level the inside
surface
The chimney bellmouth was then welded to the MS flanges using a 3.2 mm diameter
welding rod as shown in Figure 3.12. The inner diameter of the flange was tapered to
match the profile curve of the inner radius of the chimney bellmouth.
Figure 3.12: The chimney bellmouth fully welded together
40
The inside of the chimney bellmouth was later filled with a Bondo body filler to
ensure all the gaps are filled and also to smoothen the inner surface. The cardboard
with the profile of the inner radius of the chimney bellmouth drawn into it was again
used to exactly match the chimney bellmouth.
3.2.2 Solar Air Collector
The solar air collector is a very important component of an SCPP. The solar air
collector helps trap the hot air and guides the hot air towards the turbine section with
the help of the chimney bellmouth. The Schematic and the 3D view of the frames of
the solar air collector is show in Figure 3.13.
Figure 3.13: The 3D view and the schematic of the frames of the solar air collector
41
The frames of the solar air collector were made of 40 mm x 40 mm x 1.6 mm
galvanized steel square tubing. The square tubing were cut into correct sizes and
welded together using a 2.5 mm welding rod to provide the frame for the solar air
collector as shown in Figure 3.14.
Figure 3.14: Frames for the solar air collector
The 40 mm x 40 mm x 1.6 mm square tubing was chosen so that it provides
structural stability due to the weight of the 6 mm clear Perspex and the weight of
people who will walking on top of it during construction and testing. Once the
square tubing is properly positioned, the clear Perspex sheets were then cut to correct
sizes as shown in Figure 3.15.
42
Figure 3.15: Perspex for the solar air collector
The Perspex were then placed on top of the square tubing frame and holes were
drilled on the Perspex and the frame to ensure correct alignment is achieved as
shown in Figure 3.16.
Figure 3.16: The solar air collector pre-alignment
43
3.2.3 Solar Chimney
The chimney is also a very important component of an SCPP. It is the actual thermal
engine of the SCPP. A 1.6 mm thick galvanized sheet metal was rolled into a cone
shape for the chimney as shown in Figure 3.17. Three different sections of 1200 mm
each were made separately and welded together to complete the 3600 mm tall
chimney.
Figure 3.17: A section of a solar chimney
The smaller end of the chimney was welded to a round flange which will be fitted to
the flange on the bellmouth. A rubber pad was cut into a circular shape and placed
between the two flanges to prevent leakage.
3.2.4 Foundation
The foundation and footing details of the SCPP are shown below in Figure 3.18. The
depth of the foundation was 1000 mm.
44
Figure 3.18: Schematic of the SCPP foundation and footing details
A 40 mm x 40 mm x 4mm thick gauge MS square tubing was used as the posts for
the SCPP with a round flange welded to the top as shown in Figure 3.19. The inner
diameter of this flange was also tapered to match the other tapered flange that is
fitted to the chimney bellmouth.
Figure 3.19: The solar chimney foundation
45
A 1000 mm deep hole was dug and the SCPP structure was placed inside and
blended cement of 1: 3 ratio to gravel and sand mix was poured on top of it as shown
in Figure 3.20.
Figure 3.20: Cement being poured onto the SCPP foundation
Wire mesh 665 was placed on the ground as shown in Figure 3.21 and cement of 50
mm thickness was poured on top of it to act as the absorber.
Figure 3.21: Wire mesh 665 on top of the ground surface before cement is poured
46
The absorber was then painted black to improve its absorbing capabilities as shown
in Figure 3.22. The black painted surface absorbs and emits heat better than a non
painted surface.
Figure 3.22: The solar air collector sitting on the black painted cement absorber
3.2.5 The 4m Tall Experimental SCPP
Four temperature sensors (PT – 100) were fitted across one side of the collector and
three PT – 100 sensors were fitted along the chimney height. A pitot static tube was
fitted a little above the throat of the chimney. The chimney was then fitted to the
collector and bolted. Eight M16 high tensile bolts were used to secure the
components together. Three 5 mm diameter galvanized steel guy wires were
suspended from the chimney top and were secure at angles of 120 on the ground
using augers. The completed 4m tall experimental SCPP is shown in Figure 3.23.
47
Figure 3.23: The 4m tall experimental SCPP
A DaqPRO datalogger was used to log the temperature data while a Furness Controls
digital micromanometer model FCO510 was used to measure the dynamic pressure
which was interfaced to a Windows XP laptop using RS 232 cable. The values of
dynamic pressures were saved in a Microsoft Excel file. Then the dynamic pressures
were converted into the corresponding velocities.
3.2.6 PT – 100 Temperature Sensor
A PT – 100 temperature sensor (2 wire) as shown in Figure 3.24 was used for
temperature measurements across the collector and along the chimney height. The
specifications of the sensor is given in Table 3.1 [66].
48
Figure 3.24: PT – 100 Temperature sensor [66]
Table 3.1: PT – 100 Temperature Sensor Specifications Range -200 – 400 ⁰C
Resolution 0.1 ⁰C (7 mΩ)
Accuracy -200 to -50 ± 0.5%
50 to 400 ± 0.5%
-50 to 50 ± 0.5 ⁰C
Teflon Cable Length 2.5 m
Teflon Cable Range -65 to 200 ⁰C
3.2.7 DaqPRO Datalogger
A DaqPRO datalogger as shown in Figure 3.25 was used to log and store
temperature data. The DaqPRO data logger is a portable battery operated acquisition
and logging system with 8 channel data logging capabilities. The specifications for
the DaqPRO data logger is shown in Table 3.2 [67].
49
Figure 3.25: The DaqPro datalogger [67]
Table 3.2: DaqPRO Datalogger Specifications
0 to 24 mA
Range 0 to 24 mA
Resolution 4.76 μA
Accuracy ± 0.5 %
Loop Impedance 21 Ω
0 to 50 mV
Range 0 to 50 mV
Resolution 3 μV
Accuracy ± 0.5 %
0 to 10 V
Range 0 to 10 V
Resolution 200 μV
Accuracy ± 0.5 %
50
Input Impedance 125 KΩ
Temperature PT – 100
Range -200 to 400 ⁰C
Resolution 0.1 ⁰C (7 mΩ)
Accuracy -200 to -50 ± 0.5 %
50 to 400 ± 0.5 %
-50 to 50 ± 0.5 ⁰C
Communication
USB 1.1 Compliant
Sampling
Capacity 512 KB
Analog Sampling Rate 1 sample/ hour to 4000 samples sec, 1
channel
Analog Sampling Resolution 16 – bit
Channel Separation 80 db
Main Machine Interface
Full Keyboard Operation – Enables manual programming of the logger
Graphics LCD 64 x 128 pixels
Power Supply
Internal Rechargeable 7.2 V NiMH battery
Built – in Battery Charger
External 9 to 12 V DC Input
Battery Life 25 hours between charges
Operating Temperature Range
0 to 50 ⁰C
Casing
Plastic ABS Box
Dimensions 182 x 100 x 28 mm
Weight 450 gr
51
3.2.8 Pitot – Static Tube
A standard pitot static tube shown in Figure 3.26 was used for pressure
measurements for the SCPP. The pitot – static tube was properly aligned so that that
flow is parallel to it. The pitot – static tube was connected to the FC0510 digital
micromanometer to measure the dynamic pressure readings.
Figure 3.26: A Pitot – Static tube
3.2.9 Furness Controls Digital Micromanometer FCO510
A Furness Controls digital micromanometer model FCO510 shown in Figure 3.27
was used to measure the dynamic pressure for the SCPP. The digital
micromanometer can be interfaced with a computer via RS 232 cable. The pressure
readings are then logged into the computer in a Microsoft Excel format. The
52
specifications of the Furness Controls digital micromanometer model FCO510 is
shown in Table 3. 3 [68].
Figure 3.27: Furness Controls Digital Micromanometer
Table 3. 3: Furness Controls Digital Micromanometer Specifications
Power Requirements Rechargeable batteries (8 hours run
time), or 12 V DC (minimum 350 mA),
or 90 – 240 V AC power 50 – 60 Hz
Instrument Range (dual) 0 – 0.8 “H2O and 0 – 8.0 “H2O (5
significant figures per range)
Accuracy Calibration to 0.25% of reading or 0.1%
of reading between 10% of lowest range
and full scale, +/- one digit.
Storage Temperature -10 to 50 C
Working Temperature 0 to 45 C
DC Outputs 18V DC 25mA for 4 to 20 mA sensors
Analog Outputs 0 to 5V DC, 12 bit resolution (1 in 4096)
Maximum Overload 10 times instrument differential
53
Maximum Static 10 bar applied to both + and - ports
simultaneously
Pneumatic Fittings 6mm OD by 4mm ID tube
Flow Devices 8” Standard Pitot Tube (other sizes
available upon request)
Absolute Pressure Range Preset value 0 to 11bar (external sensor
option n/a)
Relative Viscosity Range 0.1 to 3.0
Relative Density Range 0.1 to 3.0
Pitot K Factor Range 0.5 to 3.0
D.P. Units Pa, kPa, mmH2O, “H2O, ubar, mbar,
mmHg, “Hg, thou, NM-2, PSF, PSI
Display Average Time 1 to 20 seconds
Display Update Time 2 1⁄2 times per second
Bar Graph Update Time 5 times per second
Analog Output Update Time 2 1⁄2 times a sec
Data Logger Time Interval 1 to 3600 sec (1 hour)
Data Logger Buffer Size 300 data values
54
4. Results and Discussions
4.1 Numerical Results for the 10m SCPP
The numerical simulation results are presented in this section. The overall height of
the SCPP was 10 m and the solar air collector was 8 m in diameter. The collector
inlet opening and the chimney divergence angle were varied in this work, as shown
in Figure 4.1.
Figure 4.1: Schematic diagram of the SCPP with the various parameters that were studied
Different configurations of the SCPP were tested out and are made into cases for
ease of understanding as shown in Table 4.1. The collector base height was varied
from 0.5 m, 0.75 m and 1 m from the ground level. The collector outlet diameter was
varied from 0.6 m to 1 m and the chimney throat diameter was varied from 0.25 m to
0.3 m, as shown in Table 4.1. All of these combinations were tested for collector
inlet openings of 0.05 m, 0.10 m, 0.15 m and 0.20 m and divergence angles of 0 to
3 in increments of 1 .
55
Table 4.1: Different Configurations of the 10 m SCPP Tested Cases Collector Outlet
Height (m)
Collector Outlet
Diameter (m)
Chimney Throat
Diameter (m)
1 0.5 0.6 0.25
2 0.5 0.6 0.3
3 0.5 1 0.25
4 0.5 1 0.3
5 0.75 0.6 0.25
6 0.75 0.6 0.3
7 0.75 1 0.25
8 0.75 1 0.3
9 1 0.6 0.25
10 1 0.6 0.3
11 1 1 0.25
12 1 1 0.3
The power available for the turbine was calculated using:
(35)
The power available was calculated at the measurement location, shown in Figure
4.1, where the maximum air velocity was recorded.
Figure 4.2 shows the power available at different chimney divergence angles for all
collector inlet openings for case 5. The available power was the highest for the 0.05
m opening and lowest for the 0.2 m opening. The peak available power was observed
at divergence angle of 2 . It can also be noted that SCPP’s with a divergence
chimney configurations produced more available power compared to the SCPP with
a straight tower (0 divergence angle). This is due to the increase in mass flow rate
and velocity, hence higher kinetic energy compared to a straight tower [44]. The
high values of available power for 0.05 m opening are due to the high values of mass
flow rate and velocity compared to other collector openings. The high mass flow
rates and velocities are caused by very little interaction of the heated air in the solar
air collector with the ambient temperature and this creates a large heating area in the
56
solar air collector; this results in air getting heated up faster and rising through the
chimney; consequently more fresh air is drawn into the collector from the opening.
For the collector opening of 0.2 m, the air inside the solar air collector interacts more
with the ambient air and causing a lesser heating of air in the solar air collector.
Similar trends were observed for other cases. According to Pretorius and Kroger
[22], a lower collector inlet opening results in a smaller collector flow area, thus
having high collector air velocities. In real cases, atmospheric winds play a major
role in the performance of an SCPP. Strong atmospheric winds result in a total
degradation on the performance of an SCPP while weak atmospheric winds also
affect the performance of an SCPP unless the collector inlet opening is kept low
[39].
Figure 4.2: Power available for case 5 for various collector inlet openings and various
chimney divergence angles.
Figure 4.3 shows the temperature distribution on the collector for the 0.05 m opening
case. It can be seen that the temperature is higher over a large area near the center of
the collector. This caused the faster heating up of the air and flow through the
57
chimney, and drawing more fresh air, as described above. Compared to this, when
the opening is 0.2 m, the temperature is lower in the same area as the case for Figure
4.4. This causes the flow through the chimney to be less compared to the 0.05 m
opening case. Hence, the power available for the 0.05 m opening is much higher
compared to the 0.2 m opening, as shown in Figure 4.2. The “temperature stems”
inside the collector is due to the differential heating of the ground surface.
Figure 4.3: Temperature contours on the collector for collector inlet opening of 0.05 m
Figure 4.4: Temperature contours on the collector for a collector inlet opening of 0.2 m
58
Figure 4.5 shows the power available for a constant collector inlet opening of 0.1 m
at different chimney divergence angles for case 1, case 5 and case 9. The collector
outlet diameter is 0.6 m for all the cases. The available power was the highest for
case 5 (collector outlet height of 0.75 m) and lowest for case 1 (collector outlet
height of 0.5 m). The high values of available power for case 5 are due to the high
values of mass flow rate and velocity compared to other collector outlet heights. The
low values of available power in case 1 are due to the lower volume of air entering
the chimney. When the hot air near the collector opening interacts with the ambient
air outside the collector due to natural convection taking place, about 1/3 the radius
of the collector gets affected by this phenomenon and this cause less air to rise up in
the collector entering the chimney. This interaction of the heated air and the ambient
air is similar in all the three cases, but for case 5, due to the higher collector outlet
height, enough air enters the chimney with less collision between air particles. For
case 9, it is similar to case 5 but due to the larger collector outlet height; more
collisions of air particles take place since the chimney inlet diameter is small, thus
affecting the overall performance of the SCPP. Similar trends were observed for
other cases. According to a study conducted by Pretorius and Kroger [22], although
a lower collector outlet has a good ground energy extraction resulting in a higher
collector airflow velocities, it also has high energy losses through the collector roof
to the environment and vice – versa. According to them, an optimal collector
configuration should take into account the plant power output, the plant dimension
and the construction cost as optimization constraints.
59
Figure 4.5: Power available for cases 1, 5 and 9 for the collector inlet openings of 0.1 m and different chimney divergence angles
Figure 4.6 shows the power available for a constant collector opening of 0.1 m at
different chimney divergence angles for case 3, case 7 and case 11. These cases are
similar to cases 1, 5, and 9 but with a different collector outlet diameter of 1 m. The
available power was the highest for case 7 and lowest for case 3. The high values of
available power for case 7 are due to the higher mass flow rates and velocities
compared to other collector outlet heights. Also, compared to Fig. 4.5, Fig.4.6 has
higher available power peaks for all collector outlet heights. The larger collector
outlet diameter of 1 m increases the volume of air entering the chimney as the
resistance to the flow is less for this case, thus having higher available power.
Similar trends were observed for other cases. It can be concluded from Figure 4.5
and Figure 4.6 that the collector outlet diameter is a very important factor in the
design of an SCPP and by increasing the collector outlet diameter, the power
available can be increased significantly due to the higher mass flow rates and
velocities. Figure 4.7 shows a better representation of cases 1, 3, 5, 7, 9 and 11
combined together for a constant collector opening of 0.1 m at different divergence
angles. It is clearly seen that the available power for the collector outlet diameter of 1
60
m is higher than that of the collector outlet diameter of 0.6 m in all the respective
cases.
Figure 4.6: Power available for cases 3, 7 and 11 for the collector inlet openings of 0.1 m and different chimney divergence angles
[
Figure 4.7: Power available for cases 1, 3, 5, 7, 9 and 11 for the collector inlet opening of 0.1 m and different chimney divergence angles
61
Figure 4.8 shows the power available for a constant collector opening of 0.1 m at
different values of chimney divergence angle for case 2, case 6 and case 10. These
cases are similar to cases 1, 5, and 9 but with a chimney throat diameter of 0.3 m.
The available power is the highest for case 6 and lowest for case 2 showing a trend
similar to Figure 4.5. The high values of available power for case 6 are due to the
high values of mass flow rate and velocity compared to other collector outlet heights.
The low values of available power in case 2 are due to the lower volume of air
entering the chimney. By comparing Figure 4.5 and Figure 4.8, it can be noted that
the overall trends are similar but the magnitude of the power available is different.
The higher power available in case 2 compared to case 1 is mainly due to the higher
mass flow rate of air entering the chimney. However, for case 5 and case 6, even
though the mass flow rate was higher for case 6, the power available was still higher
for case 5 due to the higher velocity caused by the smaller chimney diameter which
acts as a nozzle increasing the velocity of air entering the chimney. Figure 4.9 shows
a better representation of cases 1, 2, 5, 6, 9 and 10 combined together for a constant
collector opening of 0.1 m at different values of chimney divergence angle.
Figure 4.8: Power available for cases 2, 6 and 10 for the collector inlet opening of 0.1 m and different chimney divergence angles
62
Figure 4.9: Power available for cases 1, 2, 5, 6, 9 and 10 for the collector inlet opening of 0.1 m and different chimney divergence angles
Figure 4.10 shows the velocity vectors for case 3 which has the highest available
power compared to all other cases. Case 3 has a collector opening of 0.05 m with a
collector height of 0.5 m. The collector outlet diameter was 1 m with a chimney
diameter of 0.25 m diverging at 2 . The maximum available power for this case is
14.504 W. The maximum velocity achieved is 7.864 m/s and the mass flow rate is
0.469 kg/s. Figure 4.11 shows the temperature contours for case 3. The temperature
is higher towards the center of the collector. Figure 4.12 shows the temperature
variation along the chimney for case 3. It can be seen that the temperature generally
decreases up to a height of 4 m and slightly increases afterwards. This slight increase
in temperature is very small (less than 1 K) and may be due to the friction at the wall
of the chimney. The decrease in air temperature is due to the pressure drop through
isentropic relation [46]. An experimental study conducted by Zhou et al. [7] showed
a general decrease in air temperature along the chimney height. The overall
temperature variation along the chimney is very similar for both experimental and
CFD results.
63
Figure 4.10: Velocity vectors on the entire SCPP for case 3 for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰
Figure 4.11: Temperature contours on the entire SCPP for case 3 for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰
64
Figure 4.12: Temperature variation along the chimney height for case 3 for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰
Figure 4.13 shows the velocity variation along the chimney for case 3. The velocity
generally increases to a height of 1 m and then decreases afterwards. The increase in
velocity is due to the reduction in area (nozzle effect) and decreases due to the
diverging duct. Similar trends were also observed by Koonsrisuk and Chitsomboon
[44], Sangi et al. [56] and Chergui et al. [69] in their study of an SCPP.
65
Figure 4.13: Velocity variation along the chimney height for case 3 for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰
Figure 4.14 shows the temperature at a height of 0.025 m along the radius of the
collector from the outer periphery to the center. The temperature inside the collector
increases from the ambient temperature of 303 K at the outer periphery to a
temperature of 321 K at about 0.8 m inside the collector. The temperature remains
essentially constant away from the collector edges. The temperature rise inside the
collector towards the chimney is due to the air accumulating thermal energy as it
travels towards the collector outlet/ chimney inlet [46]. These trends were very
similar to the experimental results obtained by Zhou et al. [7]. The temperature
difference was also very similar to that experimental study.
66
Figure 4.14: Temperature variation along the outer radius of the collector to the center measured at 0.025 m above ground for case 3 for the collector inlet opening of 0.05 m
and chimney divergence angle of 2⁰
Figure 4.15 shows the temperature variation from the base of the collector to the
collector outlet at the center of the tower. The temperature decreases as the air rises
up towards the chimney. The maximum temperature change inside the collector is 17
degrees. Figure 4.16 shows the velocity variation from the base of the collector to the
collector outlet at the center of the tower. The velocity increases towards the throat
of the chimney. Figure 4.17 shows the temperature from the base of the collector to
the top of the chimney. The temperature essentially drops although there is a small
increase towards the chimney exit. Previous works also reported a drop in
temperature towards the chimney outlet [46]. Figure 4.18 shows the velocity from
the base of the collector to the top of the chimney. The velocity increases till the
throat where the maximum velocity is recorded; after which the velocity starts to
decrease till close to the chimney outlet, after which there is a small increase in
velocity probably due to the temperature difference between the chimney air and the
ambient air.
67
Figure 4.15: Temperature variation from the ground to the collector outlet at the
center for case 3 for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰
Figure 4.16: Velocity variation from the ground to the collector outlet at the center for case 3 for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰
68
Figure 4.17: Temperature variation from the ground to the top of the chimney for case 3 for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰
Figure 4.18: Velocity variation from the ground to the top of the chimney for case 3 for the collector inlet opening of 0.05 m and chimney divergence angle of 2⁰
69
4.2 Numerical and Experimental Results for the 4 m Tall SCPP
The numerical simulation and the experimental results of the 4 m SCPP are
presented in this section.
A scaled down model of 1:2.5 of the 10 m SCPP was simulated and presented in this
section. The overall height of the SCPP was 4 m and the overall collector diameter
was 3.2 m. Divergence angle of 2 was chosen since it produced best results in the
10 m tower. The collector outlet height was kept constant at 0.2 m. The collector
outlet diameter, the collector opening height and the chimney throat diameter were
varied. The collector outlet diameter was varied from 0.24 m to 0.4 m and the
collector inlet opening was varied from 0.02 m to 0.10 m at increments of 0.02 m.
The chimney throat diameter was varied from 0.10 m to 0.12 m. Different
configurations of the 4m tall SCPP were tested out and are made into cases for ease
of understanding as shown in Table 4.2. All these cases were tested with all the
collector inlet openings. The locations for temperature sensors and the pressure
sensor are shown in Figure 4.19.
Table 4.2: Different Configurations of the 4 m SCPP Tested Cases Collector Outlet
Diameter (m)
Chimney Throat
Diameter (m)
A 0.24 0.10
B 0.4 0.10
C 0.24 0.12
D 0.4 0.12
70
Figure 4.19: Temperature and pressure sensors measurement locations
Figure 4.20 shows the power available for all different configurations of the 4 m
SCPP. It can be clearly seen that highest power available of 0.57 W was achieved in
case B at collector inlet opening of 0.02 m. Case D had higher available power in
almost all collector inlet openings except for collector inlet opening of 0.02 m.
Collector inlet opening of 0.02 m had the highest available power in almost all cases
and the collector inlet opening of 0.10 m had the lowest available power in all cases
except for case D where the highest available power was achieved at collector inlet
opening of 0.04 m. The larger collector outlet diameter of 0.4 m had higher available
power compared to the smaller collector outlet diameter of 0.24 m having the same
chimney throat diameter in all respective cases. This is due to the higher volume of
air being allowed to enter the chimney. It can also be noted that chimney throat
diameter of 0.12 m had higher available power compared to chimney throat diameter
of 0.10 m in almost all collector inlet openings.
71
Figure 4.20: Power available for cases A, B, C and D for the chimney divergence angle of 2 and different collector inlet openings
Figure 4.21 shows the mass flow rate for all different configurations of the 4 m
SCPP. It can be clearly seen that highest mass flow rate of 0.063 kg/s was achieved
in case D at collector inlet opening of 0.04 m. Case D had higher mass flow rate in
all collector inlet openings. Collector inlet opening of 0.02 m had the highest mass
flow rate in almost all cases and the collector inlet opening of 0.10 m had the lowest
mass flow rate in all cases except for case D where the highest flow rate was
achieved at collector inlet opening of 0.04 m. The larger collector outlet diameter of
0.4 m had higher mass flow rate compared to the smaller collector outlet diameter of
0.24 m having the same chimney throat diameter in all respective cases. It can also
be noted that chimney throat diameter of 0.12 m had higher mass flow rate
compared to chimney throat diameter of 0.10 m in almost all collector inlet
openings.
72
Figure 4.21: Mass flow rate for cases A, B, C and D for the chimney divergence angle of 2 and different collector inlet openings
Figure 4.22 shows the air velocity for all different configurations of the 4 m SCPP. It
can be clearly seen that highest velocity of 4.673 m/s was achieved in case B at
collector inlet opening of 0.02 m. Case B had higher velocity in all collector inlet
openings. Collector inlet opening of 0.02 m had the highest velocity in almost all
cases and the collector inlet opening of 0.10 m had the lowest velocity in all cases
except for case D where the highest velocity was achieved at collector inlet opening
of 0.04 m. The larger collector outlet diameter of 0.4 m had higher velocity
compared to the smaller collector outlet diameter of 0.24 m having the same
chimney throat diameter in all respective cases. It can also be noted that chimney
throat diameter of 0.10 m had higher velocity compared to chimney throat diameter
of 0.12 m in almost all collector inlet openings.
73
Figure 4.22: Velocity for cases A, B, C and D for the chimney divergence angle of 2 and different collector inlet openings
Based on the simulation results, case D with collector inlet opening of 0.04 m was
selected for fabrication due to the high mass flow rate and high velocity, hence high
available power. Figure 4.23 shows the velocity vectors for case D. The highest
velocity achieved was 4.05 m/s just above the chimney throat diameter.
74
Figure 4.23: Velocity vectors on the entire SCPP for case D for the collector inlet opening of 0.04 m
Figure 4.24 shows the temperature contours for case D. The temperature of air inside
the collector slowly increases from outer radius to the inner periphery. Very high
temperature is achieved in the center of the collector due to hot air rising quickly and
accelerating towards the chimney bellmouth. The temperature along the chimney
decreases very slightly.
75
Figure 4.24: Temperature contours on the entire SCPP for case D for the collector inlet opening of 0.04 m
Figure 4.25 shows the temperature variations across the collector for both the CFX
results and the experiment results. The temperature was measured at 1.57 pm on the
6th of December, 2013. The average ambient temperature was 30⁰C and the average
ground temperature was 50⁰C which matched the conditions used in the simulation.
It can be seen that temperature increases towards the center of the collector for both
cases and the trends are similar. The CFX results show a larger temperature
difference compared to the experimental results. The temperature readings inside the
collector for the experimental case were generally higher than that of the CFX case.
This is due to the temperature sensor being very close to the absorber.
76
Figure 4.25: Temperature variation along the outer radius of the collector to the center
measured at various locations for both experimental and CFD for case D for the collector inlet opening of 0.04 m
Figure 4.26 shows the temperature variations along the chimney for both the CFX
results and experimental results. The temperature was measured at 1.57 pm on the 6th
of December, 2013. The average ambient temperature was 30⁰C and the average
ground temperature was 50⁰C which matched the conditions used in the simulation.
The average air velocity near the chimney throat was 3.78m/s. It can be seen that
temperature decreases along the chimney height and both the trends are similar. The
decrease in temperature along the chimney is very low (approximately 1 ) for both
the CFX results and experimental results.
77
Figure 4.26: Temperature variation along the chimney height for both experimental
and CFD for case D for the collector inlet opening of 0.04 m
Figure 4.27 shows the temperature variation across the collector at every 1 hour
interval from 9.00 am to 8.00 pm on the 6th of December, 2013. The average ambient
temperature was 30 C. There is a general increase in temperature from the outer
periphery towards the center except for the temperature variation at 3.00 pm and
4.00 pm. This may be due to temperature sensors 1 – 3 being exposed to direct
sunlight.
78
Figure 4.27: Temperature variation across the collector from 9:00 am to 8:00 pm on a typical day
Figure 4.28 shows the temperature variation along the chimney height at every 1
hour interval from 9.00 am to 8.00 pm on the 6th of December, 2013. The average
ambient temperature was 30 C. There is a general decrease in temperature from the
chimney bottom to the chimney top except for the temperature variation at 1.00 pm.
This high value of temperature at the outer periphery is caused by the PT – 100
sensor being exposed to direct sunlight. This is not the correct temperature of the air
inside the collector. The PT – 100 sensor at the chimney bottom shows the correct
temperature since it’s not being affected by direct sunlight due to the shadow
produced by the chimney.
79
Figure 4.28: Temperature variation along the chimney from 9:00 am to 8:00 pm on a typical day
4.3 The 100m SCPP Numerical Results The numerical simulation results for the 100 m SCPP are presented in this section. A
scaled up model of 10:1 of the 10 m SCPP was simulated and presented in this
section. The overall height of the SCPP was 100 m and the overall collector diameter
was 80 m. The collector inlet opening was 0.5 m and the collector outlet height was
5 m. The collector outlet diameter was 10 m and the chimney throat diameter was
2.5 m. The chimney divergence angle was 2 .
Figure 4.29 shows the temperature variation from the ground to the top of the
chimney. It can be clearly seen that the temperature decreases with height. The
decrease in temperature with height is about 3 C. Similar trends were observed with
studies conducted by Koonsrisuk and Chitsomboon [44, 46] on a similar sized tower.
80
Figure 4.29: Temperature variation from the ground to the top of the chimney for the 100 m SCPP
Figure 4. 30 shows the velocity variation from the ground to the top of the chimney.
It can be seen that the velocity intially increases from the ground to the chimney
throat and then decreases with increase in height. The increase in velocity is due to
the shape of the chimney bellmouth which acts as a nozzle. The maximum kinetic
energy is achieved just above the chimney throat. The maximum velocity achieved
was 22.72 m/s. Similar trends were observed with studies conducted by Koonsrisuk
and Chitsomboon [44] on a similar sized tower.
81
Figure 4. 30: Velocity variation from the ground to the top of the chimney for the 100 m SCPP
Figure 4.31 shows the temperature at a height of 0.025 m along the radius of the
collector from the outer periphery to the center. The temperature inside the collector
increases from the ambient temperature of 303 K at the outer periphery to a
temperature of 318 K at about halfway inside the collector. The temperature then
decreases as it move towards center of the collector due to the hot air moving up fast
through the chimney. The air in the middle of the collector rises up very quickly and
causes abrupt changes in temperature in accordance to the conservation of energy
principle [44].
82
Figure 4.31: Temperature variation along the outer radius of the collector to the center measured at 0.025 m for the 100 m SCPP
This SCPP design gives a maximum available power of 35.8 kW. The maximum
velocity achieved in the tower was 22.72 m/s and the maximum mass flow rate
achieved was 137.31 kg/s. Such a plant will be suitable to meet the power
requirements of small islands in Pacific Island Countries where the requirements are
of the order of tens of kilowatts.
83
5. Conclusions
The effect of various geometric parameters on an SCPP are presented. It can be
concluded that increasing the collector inlet opening affects the overall performance
of an SCPP. Smaller collector inlet openings performs better than larger collector
openings. The collector outlet height is also a very important parameter in the design
of an SCPP. The collector outlet should not be too high or too low. It should be at an
optimum height to provide best performance for an SCPP. The collector outlet
diameter/chimney inlet diameter is also an important parameter in the design of an
SCPP. This parameter determines the amount of air entering the chimney which has
a direct relationship to the power available. The chimney throat diameter is also an
important parameter since it determines the amount of air that will be interacting
with the turbine. A larger chimney throat diameter will allow a larger turbine to be
fitted thus, more power can be extracted. The shape of the chimney is an important
parameter in the design of an SCPP. The divergent chimney design performs better
than a straight tower or a converging tower in terms of mass flow rate and kinetic
energy. All these geometrical parameters will help improve the performance of an
SCPP. For future studies, a multiple turbine system with a divergent tower can be
designed and simulated to help extract more power.
84
6. References
[1] R. F. Service. (2005) Solar Energy: Is It Time to Shoot for the Sun? Science.
548-551.
[2] Wikipedia. (2013, 10/05/2013). World Energy Consumption. Available:
http://en.wikipedia.org/wiki/World_energy_consumption
[3] J. Schlaich and W. Schiel, "Solar Chimneys," in Encyclopedia of Physical
Science and Technology, 3rd ed, 2000, pp. 1-10.
[4] X. Zhou, J. Yang, B. Xiao, G. Hou, and F. Xing, "Analysis of chimney height
for solar chimney power plant," Applied Thermal Engineering, vol. 29, pp.
178-185, 2009.
[5] (2011, 9th June). World energy consumption. Available:
http://en.wikipedia.org/wiki/World_energy_consumption
[6] M. A. d. S. Bernardes, "Solar Chimney Power Plants - Developments and
Advancements," in Solar Energy, R. D. Rugescu, Ed., ed Croatia, 2010, p.
432.
[7] X. Zhou, J. Yang, B. Xiao, and G. Hou, "Experimental study of temperature
field in a solar chimney power setup," Applied Thermal Engineering, vol. 27,
pp. 2044-2050, 2007.
[8] M. Tingzhen, L. Wei, X. Guoling, X. Yanbin, G. Xuhu, and P. Yuan,
"Numerical simulation of the solar chimney power plant systems coupled
with turbine," Renewable Energy, vol. 33, pp. 897-905, 2008.
85
[9] X. Zhou, J. Yang, B. Xiao, G. Hou, and F. Xing, "Analysis of chimney height
for solar chimney power plant," Applied Thermal Engineering, vol. 29, pp.
178-185, 2009.
[10] Wikipedia. (2012, 2nd August). Solar updraft tower. Available:
http://en.wikipedia.org/wiki/Solar_updraft_tower
[11] T. Bosschaert. (2009, 26/04/2013). Solar Updraft Tower Upgrade:
Improving vertical updraft towers for renewable energy. Available:
http://www.except.nl/en/articles/93-solar-updraft-tower-upgrade
[12] N. Ninic, "Available energy of the air in solar chimneys and the possibilty of
its ground - level concentration," Solar Energy, vol. 80, pp. 804-811, 2006.
[13] M. A. d. S. Bernardes, A.Vob, and G. Weinrebe, "Thermal and technical
analyses of solar chimneys," Solar Energy, vol. 75, pp. 511-524, 2003.
[14] M. O. Hamdan, "Analysis of a solar chimney power plant in the Arabian Gulf
region," Renewable Energy, vol. 36, pp. 2593-2598, 2011.
[15] N. Pasumarthi and S. A. Sherif, "Experimental and theoretical performance
of a demonstration solar chimney model - Part1: Mathematical Model
Development," International Journal of Energy Research, vol. 22, pp. 277-
288, 1998.
[16] A. A. Mostafa, M. F. Sedrak, and A. M. A. Dayem, "Performance of a Solar
Chimney Under Egyptian Weather Conditions: Numerical Simulation and
Experimental Validation," Energy Science and Technology, vol. 1, pp. 49-63,
2011.
[17] C. Philibert, "The present and future of solar thermal energy as a primary
source of energy," 2005.
86
[18] J. Schlaich, R. Bergermann, W. Schiel, and G. Weinrebe, "Design of
Commercial Solar Updrfat Tower Systems - Utilization of Solar Induced
Convective Flows for Power Generation," Journal of Solar Energy
Engineering, vol. 127, pp. 117-125, 2005.
[19] T. Bosschaert. (2008, 26/04/2013). Solar Updraft Towers: Variations and
Research. Available:
http://www.renewableenergyworld.com/rea/news/article/2008/10/solar-
updraft-towers-variations-and-research-53742
[20] X. Zhou, F. Wang, and R. M. Ochieng, "A review of solar chimney power
technology," Renewable and Sustainable Energy Reviews, vol. 14, pp. 2315-
2338, 2010.
[21] A. Koonsrisuk and T. Chitsomboon, "Accuracy of theoretical models in the
prediction of solar chimney performance," Solar Energy, vol. 83, pp. 1764-
1771, 2009.
[22] J. P. Pretorius and D. G. Kroger, "Critical evaluation of solar chimney power
plant performance," Solar Energy, vol. 80, pp. 535-544, 2006.
[23] E. P. Sakonidou, T. D. Karapantsios, A. I. Balouktsis, and D. Chassapis,
"Modelling of the optimum tilt of a solar chimney for maximum air flow,"
Solar Energy, vol. 82, pp. 80-94, 2008.
[24] Wikipedia. (2011, 26/04/2013). Project: Solar Updraft Towers Generate
Mega Power. Available:
http://www.solaripedia.com/13/371/5025/solar_updraft_tower_in_manzanare
s_spain.html
[25] T. W. v. Backstrom and A. J. Gannon, "Solar chimney turbine
characteristics," Solar Energy, vol. 76, pp. 235-241, 2004.
87
[26] S. Bergermann. (26/04/2013). Solar Updraft Tower. Available:
http://www.solar-updraft-
tower.com/de/technical_concept/prototype_manzanares
[27] T. W. v. Backstrom and A. J. Gannon, "The solar chimney air standard
thermodynamic cycle," Research and Development Journal, vol. 16, pp. 16-
24, 1999.
[28] H. Cohen, G. F. C. Rogers, and H. I. H. Saravanamutto, Gas Turbine Theory,
3rd ed., 1987.
[29] R. D. Archer and M. Saarlas, An Introduction to Aerospace Propulsion. New
Jersey: Prentice Hall, 1996.
[30] L. B. Mullet, "Solar Chimney - Overall Efficiency, Design and
Performance," International Journal of Ambient Energy, vol. 8, pp. 35-40,
1987.
[31] M. M. Padki and S. A. Sherif, "Solar Chimney for medium-to-large scale
power generation," presented at the Proceedings of the Manila International
Symposium on the Development and Management of Energy Resources,
Manila, Philippines, 1989.
[32] N. Pasumarthi and S. A. Sherif, "Experimental and theoretical performance
of a demonstartion solar chimney model - Part 2: Experimental and
theoretical results and economic analysis," International Journal of Energy
Research, vol. 22, pp. 443-461, 1998.
[33] M. A. d. S. Bernardes, R. M. Valle, and M. F.-B. Cortez, "Numerical analysis
of natural laminar convection in a radial solar heater," International Journal
of Thermal Sciences, vol. 38, pp. 42-50, 1999.
88
[34] D. G. Kroger and D. Blaine, "Analysis of the Driving Potential of a Solar
Chimney Power Plant," Research and Development Journal, vol. 15, pp. 85-
94, 1999.
[35] A. J. Gannon and T. W. v. Backstrom, "Solar chimney cycle analysis with
system loss and solar collector performance," Journal of Solar Energy
Engineering, vol. 122, pp. 133-137, 2000.
[36] A. J. Gannon and T. W. v. Backstrom, "Solar chimney turbine part 1 of 2:
Design," presented at the International Solar Energy Conference, Reno, NV,
2002.
[37] A. J. Gannon and T. W. v. Backstrom, "Solar chimney turbine part 2 of 2:
Experimental reults," presented at the International Solar Energy Conference,
Reno, NV, 2002.
[38] A. J. Gannon and T. W. v. Backstrom, "Solar chimney turbine performance,"
Journal of Solar Energy Engineering, vol. 125, pp. 101-106, 2003.
[39] M. A. Serag-Eldin, "Computing flow in a solar chimny plant subject to
atmospheric winds," in Heat Transfer/Fluids Engineering Summer
Conference, Charlotte, North Carolina, 2004, pp. 1153-1162.
[40] C. F. Kirstein and T. W. v. Backstrom, "Flow through a solar chimney power
plant collector-to-chimney transition section," Journal of Solar Energy
Engineering, vol. 128, pp. 317-317, 2006.
[41] M. Tingzhen, L. Wei, and X. Guoliang, "Analytical and numerical
investigation of the solar chimney power plant systems," International
Journal of Energy Research, vol. 30, pp. 861-873, 2006.
89
[42] J. P. Pretorius and D. G. Kroger, "Thermo-economic optimization of a solar
chimney power plant," presented at the CHISA 2006 - 17th International
Congress of Chemical and Process Engineering, Prague, 2006.
[43] T. W. v. Backstrom and T. P. Fluri, "Maximum fluid power condition in solar
chimney power plants - An analytical approach," Solar Energy, vol. 80, pp.
1417-1423, 2006.
[44] A. Koonsrisuk and T. Chitsomboon, "Effect of tower area change on the
potential of solar tower," in The 2nd Joint International Conference on
"Sustainable Energy and Environment (SEE 2006)", Bangkok, Thailand,
2006, pp. 1-6.
[45] H. Huang, H. Zhang, Y. Huang, and F. Lu, "Simulation Calculation on Solar
Chimney Power Plant System," Challenges of Power Engineering and
Environment, pp. 1158-1161, 2007.
[46] A. Koonsrisuk and T. Chitsomboon, "Dynamic similarity in solar chimney
modelling," Solar Energy, vol. 81, pp. 1439-1446, 2007.
[47] P. Wei, M. Tingzhen, M. Wei, and X. Guoliang, "Research of the
optimization on the geometric dimensions of the solar chimney power plant
systems," Huazhong Univeristy of Science and Technology (Natural Science
Edition), vol. 35, pp. 80-82, 2007.
[48] J. P. Pretorius and D. G. Kroger, "Sensitivity Analysis of the Operating and
Technical Specifications of a Solar Chimney Power Plant," Journal of Solar
Energy Engineering, vol. 129, pp. 171-178, 2007.
[49] X. Zhou, J. Yang, B. Xiao, and G. Hou, "Simulation of a pilot solar chimney
thermal power generating equipment," Renewable Energy, vol. 32, pp. 1637-
1644, 2007.
90
[50] M. Tingzhen, L. Wei, P. Yuan, and X. Guoliang, "Numerical analysis of flow
and heat transfer characteristics in solar chimney power plants with energy
storage layer," Energy Conversion and Management, vol. 49, pp. 2872-2879,
2008.
[51] A. Koonsrisuk and T. Chitsomboon, "A single dimensionless variable for
solar chimney power plant modelling," Solar Energy, vol. 83, pp. 2136-2143,
2009.
[52] B. Klarin, S. Nizetic, and J. Roje, "Basic solar chimney flow improvements,"
Strojarstvo, vol. 51, pp. 465-472, 2009.
[53] T. Z. Ming, Y. Zheng, C. Liu, W. Liu, and Y. Pan, "Simple analysis on
thermal performance of solar chimney power generation systems," Journal of
Energy Institute, vol. 83, pp. 6-11, 2010.
[54] M. O. Hamdan, "Analytical thermal analysis of solar chimney power plant,"
in ASME 2010 4th International Conference on Energy Sustainability,
Phoenix, Arizona, USA, 2010, pp. 451-455.
[55] M. Hamdan, "Analysis of solar chimney power plant utilizing chimney
discrete model," Renewable Energy, vol. 56, pp. 50-54, 2013.
[56] R. Sangi, M. Amidour, and B. Hosseinizadeh, "Modelling and numerical
simulation of solar chimney power plants," Solar Energy, vol. 85, pp. 829-
838, 2011.
[57] A. B. Kasaein, E. Heidari, and S. N. Vatan, "Experimental investigation of
climatic effects on the efficiency of a solar chimney pilot power plant,"
Renewable and Sustainable Energy Reviews, vol. 15, pp. 5202-5206, 2011.
91
[58] T. Ming, X. Wang, R. K. d. Richter, W. Liu, T. Wu, and Y. Pan, "Numerical
analysis on the influence of ambient crosswind on the performance of solar
updraft power plant system," Renewable and Sustainable Energy Reviews,
vol. 16, pp. 5567-5583, 2012.
[59] T. Ming, J. Gui, R. K. d. Richter, Y. Pan, and G. Xu, "Numerical analysis on
the solar updraft power plant system with a blockage," Solar Energy, 2013.
[60] J.-y. Li, P.-h. Guo, and Y. Wang, "Effects of collector radius and chimney
height on the power output of a solar chimney power plant with turbines,"
Renewable Energy, vol. 47, pp. 21-28, 2012.
[61] M. A. d. S. Bernades and X. Zhou, "On the heat storage in Solar Updraft
Tower collectors - Water bags," Solar Energy, vol. 91, pp. 22-31, 2013.
[62] A. Inc., "CFX-Solver Theory Guide," 2011.
[63] A. Inc., "CFX-Solver Modelling Guide," ed, 2011.
[64] H. H. Al-Kayiem and Q. A. Al-Nakeeb, "Geometry Alteration Effect on a
Solar-Wind Power System," presented at the International Conference on
Energy and Environment (ICEE2006), UNITEN, Selangor, Malaysia, 2006.
[65] A. Inc., "CFX Introduction," ed, 2011.
[66] F. F. Technologies. (2013, 10/05/2013). DaqPro External Sensors.
Available: http://www.fouriersystems.com/products/8-channel/sensors.php
[67] F. F. Technologies. (2011, 10/05/2013). Daqpro Solution. Available:
http://www.fourtec.com/wp-content/uploads/2012/01/DaqPROBP.pdf
92
[68] F. Controls. (10/05/2013). Microprocessor Micromanometer FC0510.
Available: http://www.furnesscontrols.com/pdf/FCO510.pdf
[69] T. Chergui, S. Larbi, and A. Bouhdjar, "Thermo-hydrodynamic aspect
analysis of flows in solar chimney power plants - A case study," Renewable
and Sustainable Energy Reviews, vol. 14, pp. 1410-1418, 2010.