SIM UNIVERSITY
SCHOOL OF SCIENCE AND TECHNOLOGY
THERMOELECTRIC COOLED
COOLING FAN
STUDENT
SUPERVISOR
PROJECT CODE
: ROSHAN MATHEW GEORGE
E0704643 (PI NO.)
: TAN FOCK LAI
: JAN2010/ENG/051
A project report submitted to SIM University
in partial fulfilment of the requirements for the degree of
Bachelor of Engineering
November 2010
ABSTRACT
Thermoelectric cooling fans can be considered as one of the major
applications of thermoelectric modules (TEM) or thermoelectric
coolers (TEC). The main objective of this project is to design a cooling
system installed on a conventional fan. The idea of cooling is based on
Peltier effect, as when a dc current flows through TE modules it
generates a heat transfer and temperature difference across the ceramic
substrates causing one side of the module to be cold and the other side
to be hot. The purpose of the project is to make use of the cold side to
cool the ambient air to a lower temperature, so that it can be used as a
personal cooler. Besides, an attempt to design a Switching mode power
supply (SMPS) to drive the TE modules has been made. Testing and
measurements are also performed using an off shelf SMPS power
supply. A simple temperature controller to interface with the cooling
system has also been incorporated. Based on an analysis of sizing and
design of the TEC cooling fan, it can be deduced that the cooling
system is indeed feasible. Readings taken during testing also testify to
the fact that the TE cooling fan can lower the ambient temperature by 7
degree Celsius.
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ACKNOWLEDGEMENTS
I am taking this opportunity to render my sincerest thanks to Prof.Tan Fock
Lai (School of Mechanical and Aerospace Engineering, NTU) the project supervisor,
for his invaluable superintendence, profound advice and immaculate care from the
very inception of the project to its accomplishment despite his busy commitments.
My thanks are due to Mr. Rajesh, Student of NUS for providing his personal
equipments. In spite of his doctoral thesis, he found time to help me. Thanks to Mr.
Rahul on PCB layout and design advice. I am highly indebted to Fridaus, Research
Engineer in SIM University for advising in trouble shooting. Mr. Edwin has taken
many pains to procure a suitable power supply from China for testing. He too
deserves my thanks. I also thank Mr. Unmesh for his tips on solid works design.
Prof. Madhavan Nair based India was kind enough to spend much of his
invaluable time on sharing his ideas in connection with trouble shooting a SMPS
power supply. Words are quite insufficient to express my indebtedness to him.
Mr. Justin has lent me digital thermometers and anemometers. I place on
record my sincerest gratitude to him. In conclusion, I express thanks to my family and
friends for their unflinching moral support and strong motivation. Once again I thank
all concerned.
ENG 499 CAPSTONE PROJECT REPORT
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TABLE OF CONTENTS
ABSTRACT
i
ACKNOWLEDGEMENTS
ii
LIST OF FIGURES
v
LIST OF TABLES
vii
LIST OF SYMBOLS
viii
CHAPTER 1: INTRODCUTION
1
1.1: Project Objective
2
1.2: Scope of Project
2
1.3: Proposed Approach and Method implemented
3
1.4: Project Tasks
4
1.5: Project Management–Planning and Scheduling
5
1.6: Gantt Chart
6
CHAPTER 2: LITERATURE REVIEW
8
CHAPTER 3: THERMOELECTRIC COOLING SYSTEM
12
3.1: Thermoelectric Module
12
3.2: Parameters of a Thermoelectric Module
14
3.2.1: Cold side Temperature
15
3.2.2: Hot side Temperature
15
3.2.3: Temperature Difference
15
3.2.4: Cooling Load
16
3.3: Thermoelectric Assembly - Heat Sinks
16
3.4: Coefficient of Performance
18
3.5: Power Supply and Temperature Controller
19
CHAPTER 4: THERMOELECTRIC COOLING FAN DESIGN
20
4.1: Computation of Cooling Power
22
4.2: TEC Selection
23
4.2.1: TEC Arrangement
ENG 499 CAPSTONE PROJECT REPORT
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iii
4.3: Selection of Heat sinks
25
4.4: Selection of Blower fan
26
CHAPTER 5: POWER SUPPLY DESIGN AND FABRICTAION
28
5.1: Working Principle of the Power Supply
28
5.2: Power Supply Specification
30
5.2.1: Circuit and PCB layout
31
5.2.2: Circuit Assembly and Sections
31
5.3: Voltage Regulator and Temperature Control Circuit
36
CHAPTER 6: RESULTS AND DISCUSSIONS
38
6.1: Experimental Results of the TEC fan
38
6.1.1: Problems Faced and Solutions (Cooling Assembly)
43
6.2: Testing, Troubleshooting and Problems Encountered
44
CHAPTER 7: CONCLUSION AND RECOMMENDATIONS
49
CHAPTER 8: CRTICAL REVIEW AND REFLECTIONS
51
REFERENCES
53
APPENDIX A
55
APPENDIX B
58
APPENDIX C
66
APPENDIX D
68
APPENDIX E
71
APPENDIX F
79
APPENDIX G
82
GLOSSARY
87
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LIST OF FIGURES
Figure No:
Title
Page No
Figure 1: Block diagram of the thermoelectric cooled cooling fan
3
Figure 2: Gantt chart used to track and monitor the status of the project
7
Figure 3: A typical single stage thermoelectric module
13
Figure 4: A Classic TE Module Assembly
13
Figure 5: A Cutaway of Thermoelectric Module
14
Figure 6: Characteristics temperature of relationship in a TEC
16
Figure 7: Forced convection heat sink system
17
Figure 8: Thermal Schematic
18
Figure 9: Thermoelectric cooling fan
21
Figure 10: Exploded view of the prototype
22
Figure 11: Layout of the TECs
24
Figure 12: Electrical connection of the TECs
25
Figure 13: Block diagram of the Power Supply Circuit
29
Figure 14: Schematic Diagram of 300W Power Supply
30
Figure 15: PCB top and bottom before soldering the components
32
Figure 16: PCB board after soldering all the components
33
Figure 17: Start up circuit
34
Figure 18: Switching MOSFETs
34
Figure 19: Power Transformer
35
Figure 20: Adjustable regulator and Schmitt trigger circuit
36
Figure 21: Temperature versus time (when the clips were not installed)
38
Figure 22: Temperature versus time (with clips)
39
Figure 23: Temperature at the outlet versus Voltage
40
Figure 24: Temperature at outlet
41
Figure 25: Temperature at hotside of heat sink
42
Figure 26: Temperature measurements on the cooling assembly
43
Figure 27: Rectified output from the AC line
44
Figure 28: Ground loop formed by the scope probe
45
Figure 29: Isolation transformer
45
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Figure 30: Mica Spacer
46
Figure 31: Switching MOSFET wave form on oscilloscope
46
Figure 32: DIAC pulses
47
Figure 33: Output at IC on oscilloscope
47
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LIST OF TABLES
Table No:
Title
Page No
Table 1: A Checklist consisting of the progress made and tasks done
5
Table 2: Parts list and description
21
Table 3: Dimension of the Items
22
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LIST OF SYMBOLS
Symbol
Description
Units
A
Cross section area
m2
Ab
Effective base Area of a heat sink
m2
A fin
Area of a Fin
m2
Cp
Specific heat of air
J/kgK
D
Diameter of the channel
m
f
Darcy friction factor
N/A
h
Heat transfer coefficient
W/m 2 K
H
Height of a channel
m
I
Operating Current
A
L
Length of a fin or channel
m
L
c
Corrected length for a rectangular fin
m
m
Mass flow rate of air
kg/s
N
Number of channels
N/A
P
c
Pressure drop in the circular duct
N/m 2
P
e
Electrical input power
W
P
r
Pressure drop in the rectangular channel
N/m 2
P
t
Total pressure drop
N/m 2
Q
Air flow rate
f 3 /min
Q
c
Heat load absorbed by the cold side of TEC
W
Qh
Amount of heat dissipated at the hot side of TEC
W
R
Thermal resistance
K/W
Rb
Base thermal resistance
K/W
Rf
Fin thermal resistance
K/W
R
t
Total Thermal resistance
K/W
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r
Radius
m
t
Thickness of a fin
m
T
Temperature
°C
T
c
Cold side temperature
°C
Th
Hot side temperature
°C
in
Inlet temperature
°C
out
Outlet temperature
°C
T
Ambient temperature
°C

Temperature difference
Κ
v
Velocity of the air
m/s
V
Operating Voltage
V
W
Spacing between a rectangular channel.
m
w
Width of a fin/heat sink
m

Density of air
kg/m3
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Chapter 1: Introduction
Air cooling is of significant importance in Singapore as the air in the country is
relatively humid. So there is a need to bring down the humidity. Different types of
cooling systems are available in the market. They can be classified as air cooled,
water cooled, refrigerated, and thermoelectric cooled.
Conventional compressor run cooling devices have many drawbacks pertaining
to energy efficiency and the use of CFC refrigerants. Both these factors indirectly
point to the impending scenario of global warming. As most of the electricity
generation relies on the coal power plants, which add greenhouse gases to the
atmosphere is the major cause of global warming. Although researches are going on,
better alternatives for the CFC refrigerants is still on the hunt. So instead of using
conventional air conditioning systems, other products which can efficiently cool a
person are to be devised. By using other efficient cooling mechanisms we can save
the electricity bills and also control the greenhouse gases that are currently released
into the atmosphere.
Although Thermoelectric (TE) property was discovered about two centuries ago
thermoelectric devices have only been commercialised during recent years. The
applications of TE vary from small refrigerators and electronics package cooling to
Avionic instrumentation illumination control and thermal imaging cameras. Lately a
dramatic increase in the applications of TE coolers in the industry has been observed.
It includes water chillers, cold plates, portable insulin coolers, portable beverage
containers and etc.
As conventional fans are commonly available in the market, a TE cooling
module installed on it will be an easy and efficient way to cool a person. An effort to
build a personal cooling system was the main aim of this project. Sizing and
designing of the cooling system was performed and tested with a designed DC power
supply. The conventional fan together with the cooling module can be termed as
Thermoelectric Cooled Cooling Fan or a personal TEC cooler.
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1.1 Project Objective
Air conditioning a whole room for domestic use can be waste of energy. The
idea was to build an alternative for air conditioners and to provide cooling for a
person. The project aims to design and build a miniature prototype of thermoelectric
cooling system for a conventional fan to provide cool air. The system was targeted as
a personal cooler and temperature of the cooled air should be lowered 7 to 8 degree
Celsius from ambient temperature. Secondary objective of the project includes design
of a dc power supply and a temperature controller circuit.
1.2 Scope of Project
The scope of the project is very crucial as conventional fans will only blow at
the ambient temperature of the room. The air blown out by the fan will not be
sufficiently cooled unless the room is air-conditioned. There comes the importance
and need for this thermoelectric cooling fan to cool the air.
The project involves the development of a suitable cooling module designed
with a fan to cool the air blown out by the fan. This cooling system needed to be
powered up by a DC power supply, which is designed or using a suitable off-shelf
power supply.
The project scope involves the following elements
1. Sizing and Designing of the cooling system
2. Selection of the TECs
3. Selection of Fans and Heat sinks
4. DC power supply design with temperature control.
5. Prototype Assembly and Fabrication.
6. Temperature measurements for testing.
7. Power supply testing and troubleshooting.
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1.3 Proposed Approach and Method Implemented
The project implemented a structured system analysis and design methodology
approach to achieve the project objectives. Block system analysis of the project is
shown below (Figure 1) with the aid of a straightforward block diagram. Ambient air
is blown out by the blower through a duct to the TECs. TECs are sandwiched in
between heat sinks. Cold air is blown out from one end of the cold heat sinks. The
TECs were powered by a power supply.
AC
FANS
HEAT SINK
Ambient Air
B
L
O
W
E
R
Cold Air
Hot side
TECs
Cold side
DUCT
CLUSTER OF COLD SIDE
HEAT SINKS
TEC POWER SUPPLY
Figure 1: Block diagram of the thermoelectric cooled cooling fan.
The cooling system mainly consist of the following modules
1. Blower fan (conventional fan) which acts as the primary source of air.
2. Duct which conveys the air from the blower to cluster of Al cold heat sinks.
3. One long heat sink is fitted to the hot side of TEC to absorb heat.
4. 4 Aluminium heat sinks that are attached to the cold side.
5. Six TECs are sandwiched between cold and hot heat sinks.
6. An AC source which is used to power the fans and blower.
7. Dc power supply is used to drive the TECs
8. A simple on off temperature controller is built in with the dc power supply.
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1.4 Project Tasks
This project was separated into five phases. The first phase was the preparation
and research phase. The second phase was design and selection of components. The
third phase was the fabrication and assembly of the prototype. The fourth phase was
the testing, troubleshooting and modification. The fifth and final phase was the report
and presentation phase.
Phase 1 – The first phase of the project involved the project proposal, getting the
approval of the project proposal, drafting of the project plan and gathering of the
information needed for the project. A thorough literature review was also conducted
to expand one’s knowledge. The author also started familiarising himself with TEC.
Phase 2 – The second phase involved in-depth research on selection of TECs and heat
sinks.
A Design for the cooling section was confirmed in this phase. Various
calculations regarding the selection of heat sinks, TEC and blower fan was made. The
power supply circuit and temperature controller circuit was confirmed and designed.
Drawings for the electronic circuits with ALTUIM design tool and mechanical
designs with solid works were also made during this phase.
Phase 3 – During this phase, the author primarily continued learning on the ALTUIM
software to draw the PCB layout for the Power Supply circuit. PCB was outsourced
for printing. All the purchased components were soldered onto the board. On the other
hand the Assembly of the TECs, heat sinks, fans, clips etc were done.
Phase 4 – This was the most challenging phase where by troubleshooting of the
power supply board was carried out. Different temperature readings and
measurements were taken from the cooling system prototype. Certain modifications
were made on the prototype as well as on the power supply circuitry.
Phase 5 – During this phase, more time was allocated to prepare for final year report
and oral/poster presentation as well as highlight areas of the project which will need
further work. A power point presentation was also done in preparation for the final
presentation.
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1.5 Project Management – Planning and Scheduling
Table 1 below shows a systematic approach on the progress made and tasks
completed.
Table 1: Checklist consisting of the progress made and tasks done
Date
Tasks completed
Phase 1: Proposal and research work
Feb 2010
i) Discussion with Supervisor on the project
Checklist
ii) Research on TEC and Heat Sinks
iii) Research on power supply design and temp
control circuit
Mar 2010
iv) Vetting and Amendment of Project Proposal
v) Review and submission
April 2010
Phase 2: Design and selection
i) Calculations for the selection of TEC
ii) Selection of TEC, Heat sinks, Fans
iii) Power supply design
iv) Selection of electronic components
May 2010
v) Schematic for Mechanical/ Electronics
Design
vi) Preparation of the Interim report
vii) Review and Submit of interim report
Phase 3: Fabrication and Assembly
i) Draw PCB layout for printing.
June 2010
ii) Purchase of TEC , Heat sinks, fans etc
iii) Procuring electronic components
July 2010
iv) Soldering of components
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v) Assembly of TECs, heat sinks-prototype
August 2010
vi) Final Fabrication of prototype and Board
Phase 4: Testing and Troubleshooting
i) Testing of power supply
ii) Trouble shooting of power supply
iii) Temp Measurements on Prototype
Sept 2010
iv) Research on more functions and modification
to the system
v) Discuss with Tutor on the evaluation and
further Improvement of the project
Oct 2010
Phase 5: Final report and Project Presentation
i) Preparation of Final Report
ii) Discuss with tutor on Final Report
iii) Review and Submit Final Report
Nov 2010
iv) Poster and Slides preparation
v) Overall project presentation
1.6 Gantt Chart
A Gantt chart can be very useful for detailed planning and proper time
allocation of the entire project. So it was efficiently used to monitor the progress of
the project. Figure 2 shows the Gantt chart utilised which was utilised for the
successful completion of the project. Testing and troubleshooting of the project took a
longer period than expected.
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Months
Week No.
Activities
Feb-10
Mar-10
Apr-10
May-10
Jun-10
Jul-10
Aug-10
Sep-10
Oct-10
Nov-10
1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4 1 2 3 4
PROPOSAL & LITERATURE
REVIEW
Discussion with Supervisor on
the project
Research on TEC & HeatSinks
Research on designing power
supply and Temperature control
circuit
Preparation of proposal
Vetting & Amendment of Project
Proposal
Review & submission
DESIGN & SELECTION
Calculations for the Selection of
TEC
Selection of TEC & Heatsinks
Power supply design
Temp Controller Design
Selection of electronic
components
Drawings for Mech & Electronics
Design
Preparation of the Interim report
Review and Submit of interim
report
FABRICATION & ASSEMBLY
PCB printing for powersupply
Sourcing of TEC , Heatsinks,
fans etc
Sourcing of electronic
componets
Soldering of components
Assembly of TECs, heat sinksprototype
Final Fabrication of prototype &
Board
TESTING &
TROUBLESHOOTING
Testing of power supply
Trouble shooting of power
supply
Temp Measurements on
Prototype
Research on more functions and
modification to the system
Discuss with Tutor on the
evaluation and further
Improvement of this project
FINAL REPORT & POSTER
PRESENTATION
Preparation of Final Report
Discuss with tutor on Final
Report
Review and Submit Final Report
Prepare Poster
Overall project presentation
Figure 2: Gantt chart used to track and monitor the status of the project
ENG 499 CAPSTONE PROJECT REPORT
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Chapter 2: Literature Review
Thermoelectric phenomenon was discovered nearly two hundred years ago.
Since last sixty years the practical applications from thermoelectric had been
exploited.
The first breakthrough that would eventually be used to form the
thermoelectric effect was discovered in 1820. Several other breakthroughs in the field
were discovered over the next few decades but their relationship was not realized for a
full 38 years. William Thomson discovered that heat is absorbed or produced when
current flows in material with a certain temperature gradient and that the heat is
proportional to both the electric current and the temperature gradient. His publication
linked all the discoveries from the preceding decades. Kryotherm, (2007)
Thermoelectric coolers which is also known as thermoelectric module or Peltier
cooler is widely used in the market for several cooling applications. Use of TE
modules often gives an answer to many critical thermal management problems, where
low to moderate amount of heat is concerned.
Certain advantages of TE coolers are it works electrically without any moving
parts, thus it becomes maintenance free and silent. They are able to cool or heat
within the same module depending on the polarity of the applied DC power.
Traditional refrigeration systems are almost impossible to be manufactured without
using chlorofluorocarbons or other chemicals that harmful to the environment. TE
devices do not use or generate gases of any kind. TE modules are noted when there is
a need to cool one specific component or area only.
Typical applications on TE coolers are many. Major ones are in Avionics, Black
Box Cooling, and Electronics Package Cooling, Water and Beverage Coolers, Long
Lasting Cooling Devices and etc. Several studies, papers and research have already
been made on TE coolers. The author had gone through few and will be highlighted in
this chapter.
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Koetzsch and Madden (2009) examined on thermoelectric cooling versus
conventional cooling in industrial enclosures. Conventional cooling systems such as
air conditioners and air-to-water heat exchangers rely on chemical refrigerants or
water to cool, or remove heat from, enclosures. Besides that refrigerants, air
conditioners use compressors, evaporators, condensers and fans to provide cooling.
For the operation of Air-to-water heat exchangers it must have a connection with the
facility’s chilled water system. On the other hand a TE cooler does not require any of
the aforementioned things required by air conditioners and air-to-water heat
exchangers. Thus TE coolers provide effective cooling without refrigerants, water or
other components such as compressors and coils to effect. It only requires TE module,
a fan and a power supply. So studies have proven that TE coolers are very useful
when used for cooling in industrial enclosures.
Certain medicines are to be transported safely and in chilled surroundings.
Inventions for keeping medicines cool have taken place with the help of TE Cooler.
McStravick, et.al (2009) had invented a medical travel pack with cooling system. The
invention has helped people suffering from chronic disease to travel with proper
supply of medicine kept at proper temperature. These insulated container using TE
modules comprises of a cold plate, heat sink, fan and a temperature sensor. A
microcontroller is in electrical communication with the TE modules and the sensor.
The device maintained a temperature of 2  C to 8  C. Thus it shows that TE cooler
helps for low temperature cooling.
Several studies related on TE coolers with regards to vehicles and are utilized
well. They can be integrated into several designs. Hyeung, et.al (2007) have done a
research on thermoelectric device to control the temperature of car- seat surface. The
device helped when the temperature is warm in summer and cold in winter.
Thermoelectric property was also implemented in pick up refrigerated trucks. Studies
based on thermoelectric cooling unit for thermostatic body on refrigerated trucks were
conducted by Bulat and Nekhoroshev (2003). In this study a comparison between the
thermoelectric cooling units with vapour-compression installations was also made,
where it showed that cost price of thermoelectric unit is four-five times cheaper than
vapour-compression cooling units. The cooling power obtained for TE cooling was
same when compared to compression cooling units.
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These are excellent examples for spot cooling property of a TE module. Once
such prototype was made by Bartlett and Sukuse (2007). They have built an airconditioned cooling helmet which used thermoelectric device. The product was
designed to give comfort for the user. The idea of cooling helmet was also discussed
by Buist and Streitwieser (1988). The 12 volt personal cooling system worked well to
cool the head of a race driver. The 225 grams helmet cooling system reduced 5 to 6
degree Celsius form ambient.
TECs are more utilized in personal cooling and Harvie (2005) invented a
personal cooling and heating system specifically designed to provide many hours of
efficiency cooling or heating when worn by an a user. It was a durable light weight
cooling specifically for harsh climatic conditions. Lauwers and Angleo (2009) had
conducted a study and development of personal cooling vest which catered to
maintain a core body temperature even at extreme conditions. So this was an
admirable example, where they made use the property of TEC to benefit for their
country’s armed forces. Several others also tried examining TEC in air cooling. One
such innovative is a thermoelectric air cooling device which is powered up by a jack
that is to inserted in to a cigarette lighter socket in a vehicle. It was studied by
Harrington (2009) and the device provided comfort cooling to a persons head and face
in a vehicle. The device also removed the heat with help of a heat sink and exhausted
away to the ambient from the user.
There are many TEC manufactures in the market and to facilitate the search, a
few of them provide downloadable software search facilities. One such software is
provided
by
Laird
Technologies
(http://www.lairdtech.com/Products/AZTec-
Software-Download/), which is an excellent tool for thermoelectric module
simulation. It can be used for the analysis and selection of TECs or TEMs. Selection
of a TEC from various manufactures can be tedious. Tan and Fok (2008) have
conducted an analytical study on method of selecting a TEC from different
manufacturers before designing a cooing system. Their purpose of study was to assist
the designers to help on developing an optimised thermoelectric cooling system
design in minimum amount of time. The designers will be benefited from this study to
implement a cooling system with TEC.
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Many of the previous studies discussed above ensure that TEC is a reliable
product to be used in a cooling system for personal use. The author is confident that
anyone who has a keen interest to design TEC cooling system and if they are willing
to trail certain methodology and sizing this report will set as good example.
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Chapter 3: Thermoelectric cooling system
To design a cooling system using thermoelectric cooler (TEC) one has to know
the basics of thermoelectric effect, thermoelectric materials and thermoelectric
cooling. Thermoelectric effect can be defined as the direct conversion of temperature
difference to electric voltage and vice versa. Thermoelectric effect covers three
different identified effects namely, the Seeback effect, Peltier effect and the Thomson
effect
A thermoelectric device will create a voltage when there is temperature
difference on each side of the device. On the other hand when a when a voltage is
applied to it, a temperature difference is created. The temperature difference is also
known as Peltier effect. Thus TEC operates by the Peltier effect, which stimulates a
difference in temperature when an electric current flows through a junction of two
dissimilar materials.
A good thermoelectric cooling design is achieved using a TEC, which is solid
state electrically driven heat exchanger. This depends on the polarity of the applied
voltage. When TEC is used for cooling, it absorbs heat from the surface to be cooled
and transfers the energy by conduction to the finned or liquid heat exchanger, which
ultimately dissipates the waste heat to the surrounding ambient air by means of
convection.
3.1 Thermoelectric Module
A standard module consists of any number of thermocouples connected in series
and sandwiched between two ceramic plates (See Figure 3). By applying a current to
the module one ceramic plate is heated while the other is cooled. The direction of the
current determines which plate is cooled. The number and size of the thermocouples
as well as the materials used in the manufacturing determine the cooling capacity.
Cooling capacity varies from fractions of Watts up to many hundreds.
Different types of TEC modules are single stage, two stage, three stage, four
stage, center hole modules etc. Single stage will be suitable for a wide range of
ENG 499 CAPSTONE PROJECT REPORT
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cooling applications with low to high heat pumping capacities. A typical single stage
is shown in Figure 3.
Figure 3: A typical single stage thermoelectric module.
A thermoelectric cooler has analogous parts. At the cold junction, energy (heat)
is absorbed by electrons as they pass from p-type (low energy) semiconductor
element, to the n-type semiconductor (high energy). The power supply provides the
energy to move the electrons. At the hot junction, energy is expelled to a heat sink as
electrons move from an n-type to a p-type. Figure 4 shows an illustration on the
assembly of a Thermoelectric cooler.
Figure 4: A Classic TE Module Assembly
Before staring to design a TEC cooling system the designer have to take note the
following into consideration.
1. Temperature to be maintained for the object that is to be cooled.
2. Heat to be removed from the cooled object.
3. Time required to attain the cooling after a DC power is applied.
ENG 499 CAPSTONE PROJECT REPORT
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4. Expected ambient temperature.
5. Space available for the module and hot side heat sink.
6. Expected temperature of hot side heat sink.
7. Power available for the TEC.
8. Controlling the temperature of the cooled object if necessary
3.2 Parameters of a Thermoelectric Module
Once it is decided that thermoelectric cooler is to be considered for cooling
system, the next step is to select the thermoelectric module or cooler that can satisfy a
particular set of requirements. Modules are available in great variety of sizes, shapes,
operating currents, operating voltages and ranges of heat pumping capacity. The
minimum specifications for finding an appropriate TEC by the designer must be based
on the following parameters. The cutaway of a TEC is shown in Figure 5.
Figure 5: A Cutaway of Thermoelectric Module
 Cold side temperature ( T )
c
 Hot side temperature ( T )
h
ENG 499 CAPSTONE PROJECT REPORT
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 Operating temperature difference (  ), which is the temperature difference
between T and T .
h
c
 Amount of heat to be absorbed at the TEC’s cold surface. This can also be
termed as heat load. It is represented as ( Q ) and the unit is Watts
c
 Operating current (I) and operating voltage (V) of the TEC.
3.2.1 Cold side temperature
If the object to be cooled is in direct contact with the cold surface of the TEC,
the required temperature can be considered the temperature of the cold side of TEC
( T ).Here in this project the object is air, which has to be cooled when passed through
c
a cluster of four Aluminium heat sinks. It is discussed in detail in the next chapter.
The aim is to cool the air flowing through the heat sinks. When this type of system is
employed the cold side temperature of the TEC is needed to be several time colder
than the ultimate desired temperature of the air.
3.2.2 Hot side temperature
The hot side temperature ( T ) is mainly based on the two factors. First
h
parameter is the temperature of the ambient air in environment to which the heat is
been rejected. Second factor is the efficiency of the heat sink that is between the hot
side of TEC and the ambient.
3.2.3 Temperature difference
The two temperatures T and T and the difference between them  is a
h
c
very important factor.  has to be accurately determined if the cooling system is
expected to be operating as desired. The following equation shows the actual  .
  T  T
h c
Actual  is not same as the system  . Actual  is the difference between
the hot and cold side of the TEC. On the other hand system  is the temperature
difference between the ambient temperature and temperature of the load to be cooled.
ENG 499 CAPSTONE PROJECT REPORT
15
Figure 6 illustrates a relationship of a classic temperature summary across a
thermoelectric system.
Figure 6: Characteristics temperature of relationship in a TEC
3.2.4 Cooling Load
The most difficult and important factor to be accurately calculated for a TEC is
the amount of heat to be removed or absorbed ( Q ) by the cold side of the TEC. In
c
this project Q was calculated by finding the product of finding the product of mass
c
flow rate of air, specific heat of air and temperature difference. Here the temperature
difference system  in the difference between the inlet temperature and outlet
temperature of the cooling system. The mathematical equation for Q is as shown
c
below.
Q  m C 
c
p
3.3 Thermoelectric Assembly - Heat Sinks
Thermoelectric Assemblies (TEAs) are cooling or heating systems attached to
the hot side of the TEC to transfer heat by air, liquid or conduction. TEAs which
dissipate heat from the hot side use heat exchangers. TEC requires heat exchangers or
heat sinks and will be damaged if operated without one. The two  s, actual  and
system  (section 3.2.1) depend on the heat sinks fitted at the hot sides or cold sides
ENG 499 CAPSTONE PROJECT REPORT
16
of TEC. The thermal resistances of the heat sinks could vary the  across the TEC
for a set ambient temperature and cooling load temperature. Therefore the thermal
resistance of the heat sinks could increase the current flowing through the TEC. The
three basic types of heat sinks are: forced convective, natural convective and liquid
cooled, where liquid cooled is the most effective. The typical allowances for  at
the hot side heat sink of a TEC are
1. 10 to 15 C for a forced air cooling system with fins.- Forced convection
2. 20 to 40 C for cooling using free convection - Natural convection.
3. 2 to 5 C for cooling using liquid heat exchangers - Liquid cooled.
There are several different types of heat exchangers available in the market. As
far this project is concerned a forced convection type of heat sink was be used based
on the  . Figure 7 shows a forced convection hot side heat sink attached with a fan.
The air blows towards the heat sink from the fan will cool down the temperature of
heat sink.
Figure 7: Forced convection heat sink system
The main heat sink parameter for the selection process is its thermal resistance.
Heat sink resistance can be termed as the measure of the capability of the sink to
dissipate the applied heat. The equation is as follows.
R
ENG 499 CAPSTONE PROJECT REPORT
Th  T
Qh
17
R is the thermal resistance (in 0 C /W or K/W) and T , T is the hot side temperature
h 
and ambient temperature respectively. Q is the heat load into the heat sink which is
h
the sum of TEC power P and heat absorbed.
e
Qh  Qc  Pe
The goal of a heat sink design is to lessen the thermal resistance. It can be
attained through exposed surface area of the heat sink. It may also require forced air
or liquid cooling. The following Figure 8 shows a simple thermal schematic of a
forced convective heat sink.
Th
R
Qh
T
Figure 8: Thermal Schematic
Typical values of heat sink thermal resistance for natural convection range is
from 0.5°C/W to 5°C/W, where as for forced convection is from 0.02°C/W to
0.5°C/W, and water cooled is from 0.005°C/W to 0.15°C/W. Most of the
thermoelectric cooling requires forced convection or water cooled heat sinks. In this
project force convective heat sink is used for the design of the cooling system.
3.4 Coefficient of Performance
The Coefficient of performance (COP) of a thermoelectric module which is
the thermal efficiency must be considered for a TE system. The selection of TEC will
also be based on the COP factor. COP is the ratio of the thermal output power and the
ENG 499 CAPSTONE PROJECT REPORT
18
electrical input power of the TEC. COP can be calculated by dividing the amount of
heat absorbed at the cold side to the input power.
COP 
QC
Pe
3.5 Power Supply and Temperature Control
Power supply and temperature control are two added items that must be
considered wisely for a successful TE system. TEC is a direct current device. The
quality of the DC current is important. Current and voltage of a TEC can be
determined by the charts provided by the manufacturer. TEC’s power is the product of
required voltage and current. (P = IV).
Temperature control is generally categorized into two groups. One is open
loop or manual and the other is closed loop or automatic. For cooling systems
normally cold side is used as basis of control. The controlled temperature is compared
to the ambient temperature. An on-off or a control using thermostat is the simplest
and easiest techniques to control the temperature of a TEC.
ENG 499 CAPSTONE PROJECT REPORT
19
Chapter 4: Thermoelectric Cooling Fan Design
The thermoelectric cooling fan design was preformed based on certain
mechanical and electrical calculations. The fan’s design was compromised on the
availability of parts in the market and budget of the project. The prototype assembly
starts with a main fan which is used to blow the ambient air through a circular duct
(Appendix A.1).The duct is attached to the blower fan and leads towards a group of
four heat sinks. The air which is passed through the duct goes into the cluster of four
heat sinks which are united together. These heat sinks acts as a channel for the air to
pass through. There are six TECs that are sandwiched between a long black heat sink
and the bunch of four heat sinks. TEC cold side or the bottom side rests on the group
of four heat sinks. The hot side or the top sides of the TECs are fastened together with
the long heat sink. The TECs were installed between the heat sinks using thermal
grease, which increases the thermal conductivity by balancing irregular surface of the
heat sinks. When the TECs are in operation cold side of the TEC cools down the heat
sink channel. Air which is coming out from the channel (i.e. cold side heat sinks H1,
H2, H3, H4) is chilled air which is lower than the ambient. The cold side heat sinks
rests on a wooden base (Appendix E, Figure E.2). There are two fans fitted on top of
the hot side heat sink. They blow air towards the hot heat sink to cool it down when
the TECs are in operation. The hot air is channeled away from the user using panels
(Appendix E Figure E.3).The whole assembly of the cold side heat sinks, hot side heat
sink, TECs and the wooden base are fitted tightly with the help of metal clips. These
metal clips are tightened together with screws and nuts.
The whole assembly is
enclosed with sheets or panels. (Appendix E, Figure E8 – E11.)
Detailed drawings drawn in solid works are enclosed in Appendix A (Figure
A1- A5). It includes the front view, rear view, isometric view, exploded view and the
side view of the internal assembly.
Figure 9 shows the cooling fans assembly without the exterior panel shows the
internal structure. The parts are labeled in the Figure accordingly. The final assembly
prototype when enclosed with panel is 50cm x 16cm x19cm.
ENG 499 CAPSTONE PROJECT REPORT
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Figure 9: Thermoelectric cooling fan
The description of components and its models numbers are listed in Table 2
below.
Table 2: Parts list and description.
S/No. MODEL
QTY DESCRIPTION
1
1 WOODEN BASE
2 SUPER ORIX GH12038HA 2 HEAT SINK FANS
3 SUPER ORIX GH14045HA 1 BLOWER FAN
4 9Y692 A00-00
4 COLD SIDE HEAT SINK
5
1 HOT SIDE HEAT SINK
6
12 CLIPS
7
1 DUCT
8 TEC1-12704
6 THERMOELECTRIC MODULES
9 SHCS M6X15
18 SCREWS
The serial numbers of each item in the above Table 2 are labelled in the following
Figure 10.
ENG 499 CAPSTONE PROJECT REPORT
21
Figure 10: Exploded view of the prototype
The dimensions of each items of the internal assembly as in Table 3.
Table 3: Dimension of the Items
S/No. Item
Dimension
1 Wooden Base
28.8cm x 10.5cm x 2cm
2 Heat sink fans
12cm x 12cm x3.8cm
3 Blower fan
16cm x 16cm x 4.7cm
4 Cold side heat sinks 25.2cm x 7.96cm x 6.8cm
5 Hot side heat sink 30cm x 10cm x 2.2cm
6 Clips
15.5cm x 14cm
7 Duct
8.5cm x 14cm
8 TECs
4cm x 4cm x 4.25 mm
4.1 Computation of cooling power
The amount of heat removed or the cooling power was determined before
selection of the TEC. Q which is the amount of heat absorbed was calculated using
c
the equation ( Q  m C  ).
c
p
ENG 499 CAPSTONE PROJECT REPORT
22
Mass flow rate ( m ) of air and is the product of density of air (  ) and volume
flow rate ( Q ). Density of air at 30 C was taken as 1.164 kg / m3 . Q was obtained
by multiplying velocity of air pass through the rectangular duct of heat sinks and the
cross section area of a heat sink. It is denoted by the equation ( Q  V  A ). Velocity
of the air passing through the duct was measured using an anemometer and resulted in
a reading of 5m / s 2 .
Cross sectional area of the rectangular duct ( W  H ) was
calculated as 0.0054128m2 and the volume flow rate was 0.02706m3 / s .
Specific heat of air ( C ) at 30 C was taken as 1007 J / kgK . As discussed
p
in section 3.2.3 the system  is the difference between the ambient temperature and
the temperature of the load to be cooled. It had been targeted to attain a temp of
23C form the ambient temperature ( 30 C ). In other words the input temperature
from the blower fan is 30 C and the expected output is 23C
  in - out  30C - 23C  7 
The amount of heat load for cooling the air through the rectangular duct was
calculated as 222 W . Please refer Appendix B.1 for detailed calculations on cooling
load.
4.2 TEC Selection
The TEC was selected considering few factors such as dimensions, Qc, power
supply and etc. The model of TECs used in this project was manufactured in China by
Hebei I.T (Shangai) Co. Ltd. (Datasheet and Charts in Appendix G). The model no.
of the module is TEC1-12704. (Please see Appendix E, Figure E-5).
The idea was to select a TEC which has a cooling power greater than the
calculated TEC. TEC1-12704 operates with an optimum voltage of 12V. It has
maximum voltage of 15.4V. At 12V it draws and maximum DC current of 4 A. The
minimum power rating or the cooling power is 37.7 W. The maximum power is 48W.
It has a maximum operating temperature of 200°C.  of the TEC are 68 when hot
side temperature is 25 C . The charts from the TEC manufacture were also analysed
while choosing the TEC.
ENG 499 CAPSTONE PROJECT REPORT
23
It had been decided to choose 6 TECs of the same model so that when the
power of all the 6 TECs is higher than the calculated cooling load. The minimum
power rating for 6 TECs added together was more than the cooling load calculated.
So it was acceptable to select the
37.7 W  6  226W  222W
The electrical power supplied to the TEC must be higher than the combined
power rating of the six TECs and it also depends on the arrangement of the TEC.
4.2.1 TEC Arrangement
The ambient air blown from the blower is channelled into goes a group of four
heat sinks which acts a rectangular duct as discussed earlier. It was decided to remove
maximum amount heat from the point when the air started to enter the first heat sink.
Keeping that in mind the first heat sink was installed with two TECs in series and the
second one also was installed with another two TECs in series. This will help to
remove more heat from of the air when air enters the duct. The third and fourth heat
sinks were installed with one TEC each and they were connected in series also. All
the two series connected TECs were connected in parallel. Figure 11 illustrates a top
view of the connection of TECs as explained above. The arrow indicates direction of
air flow.
D
Figure 11: Layout of the TECs
ENG 499 CAPSTONE PROJECT REPORT
24
Each of the TEC will be acting as loads. In other words the layout above can
also be termed as three parallel groups of two TECs in series electrically. Figure 12
shows simpler redrawn electrical connection of the TECs.
Figure 12: Electrical connection of the TECs
Total required current and voltage for the all the joined TE modules are 12A
and 24V respectively. Therefore a 300W power supply was enough for the cooling
system. The electrical power input was greater than cooling power of the TECs and
also higher than the calculated Qc. ( 300W  226 W  222 W ).
4.3 Selection of Heat sink
There were two different types of heat sink used for this project. One sort was
for the cold side and another for hot side. The initial idea of the project was to use a
hollow cylinder as duct to channel air, instead of heat sink on the cold side of the
TEC. Initial testing after the proposal stage with hollow cylinder, did not work out
well. This was because there of less heat transfer within the cylinder and the air
coming out was not cold enough. So the decision was made to use to heat sinks which
acts a rectangular duct to channel air. A total of four similar kinds of heat sinks
(9Y692 A00-00) were used. (Appendix E, Figure E-4 and E-6) .Each heat sinks have
20 fins which helped to dissipate coldness fast enough from TECs cold side.
In this project heat sinks (hot side and cold side) operate by conducting heat
or coldness from the TEC to the heat sink and then radiating to air. A better the
transfer of coldness between the two surfaces, the better the cooling will be. When the
heat sinks were attached the TECs, there will be uneven surfaces or gaps. The gap
will cause for poor heat transfer, even if it is negligible. To improve the thermal
ENG 499 CAPSTONE PROJECT REPORT
25
connection between the TECs and the heat sinks a chemical compound was used. The
heat sink compound, typically a white paste made form zinc oxide in a silicone base
ensures a good transfer of heat between the modules and the heat sinks.
4.3.1 Hot Side heat sink
The hot side heat sink used in the project was a single long one installed on the
top side of the TECs. (Appendix E, Figure E-7). As discussed in section 3.3, thermal
resistance of a heat sink is an important factor while designing a system. Appendix
B.2 shows a detailed calculation for the thermal resistance required for a suitable heat
sink. Thermal resistance found using the equation R  (Th
t
-T)

Qh
was 0.038K / W .
Therefore a forced convection heat sink had to be used.
When selecting hot side heat sink for the project other factors such as
dimension to fit into the whole assembly, budget and availability were also taken to
consideration. The heat sink was bought from a local shop and there was no thermal
resistance or datasheets available for the product. The alternative was to calculate R
t
from the resistance of the unfinned area ( Rb ) and the resistance offered by the fins
( Rf ). Since both of these resistances are acting in parallel, total resistance was found
using the equation
1
1
1
. The detailed calculations were attached in


Rt
Rb
Rf
Appendix B.2. The calculated value was 0.0145K / W .
The calculated thermal resistance of the heat sink was lesser than the required.
But when considered the dimensions of the cooling system the selected heat sink was
very apt. A drawback expected was overheating of heat sink. However bigger fans
were installed to cool the hot side heat sink to overcome this.
4.4 Selection of Blower fan
The Super Orix fan model GH14045HA operates on 240V AC with 0.18A
with a power rating of 35 W. The fan acts as a blower which blows ambient air in to
the cooling modules. The fan is attached to a circular duct; the circular duct is fitted to
a rectangular duct (cold side heat sinks). The blower fan was selected and verified
ENG 499 CAPSTONE PROJECT REPORT
26
against some important pressure drop calculations across the circular duct and the
rectangular duct. Detailed calculations on power of the fan and pressure drop are
attached in Appendix B.3.
Pressure drop of the each sections were calculated separately using Darcy’s
Equation. 0.5  (
fL
)    v 2 . Friction factor f was taken as 0.03. This is normally
D
selected from Moody’s diagram in fluid mechanics. D is the diameter of the circular
pipe. For the heat sink D was taken as 0.5 W , where W is the spacing between the
channel of fins. Pressure drop for each channel was calculated. The total pressure
drop through the heat sink = N  Pressure drop through each channel. N denotes the
number of channels. The total pressure drop will be the sum of pressure drop in
circular pipe and pressure drop in heat sink channel.
It was calculated as
1393.33 N/m2 .
Power of the fan is the product of total pressure drop and volume flow rate.
The power was obtained as 36W after calculation and it shows that the selected fan
was appropriate.
ENG 499 CAPSTONE PROJECT REPORT
27
Chapter 5: Power Supply Design and Fabrication
Thermoelectric cooling system needs a suitable deigned power supply to
operate. A Thermoelectric cooler operates from a DC power input. The power
supplies will range from batteries to closed loop temperature control power supply
circuits. A suitable power supply could be brought from market for the cooling
system. But here in this project an attempt to implement a power supply and a
temperature control circuit was done.
It was finalized to implement a switching mode power supply (SMPS) AC to
DC converter for the cooling system. When compared to a linear power supply, the
advantages of a SMPS are small size, less weight and cost with higher power
efficiency. SMPS uses the principle of continuous power transfer for the
implementation of voltage regulation. The transistors will operate as switches (on/off)
with inductors and capacitors as energy storage an SMPS transfers enough energy
from input to output to reach the required output current and voltages.
The SMPS circuit used in the project is a 300W secondary controlled twoswitch forward converter (ST Microelectronics, 2004). It is controlled with a L5991A
IC(Appendix G). A two switch forward converter with two transistors is typically
used for 100 to 300 W applications. The cooling system needs a 300W power input,
hence it had been decided to use the circuit.
5.1 Working Principle of the Power Supply Circuit
The reason for using a complicated SMPS circuit rather than a simple AC to
DC converter is because it would require a 5 to 10 kg transformer to deliver 300W
DC at normal line frequency. The basic working of the circuit can be explained as
follows. Initially the AC from the line is converted to a dc voltage using a full bridge
and input capacitors. This DC is then modulated at high frequencies using switching
MOSFETs and passed through a high frequency transformer. The resulting output at
the secondary of the transformer would be high frequency AC that has been stepped
down. This AC is passed through a half bridge and then through an inductor to obtain
a steady current. At the end there will be output capacitors that will smooth out the
voltage to a required DC.
ENG 499 CAPSTONE PROJECT REPORT
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In the circuit that is used in this project, the switching of the MOSFETS and
hence the output is controlled by L5991A controller IC. The controller gets the
feedback of the voltage and current from the secondary side of the power transformer
using through a voltage divider and current sense transformer. This feedback is used
to adjust the switching of the MOSFETS to obtain desired output. The switching is
achieved by connecting the pulses from the controller to the gate of the MOSFETs
through a pulse transformer to provide isolation. The controller obtains power from a
secondary winding on the output inductor. The circuit starts with the help of a pulse
trail obtained from a DIAC circuit is connected to the gate of MOSFETS. The
resulting power transferred to the secondary would give enough voltage for the
controller to start-up. Once turned on, the controller will regulate the outputs to
required values. Figure 13 below illustrates the designed circuit board and
temperature control circuit.
`
Line to
DC
Converter
DIAC
Circuit
Switching
MOSFETs
Pulse
Transformer
L5991A
Controller
Power
Transformer
Current
Sense
Voltage
Sense
Voltage
Regulator
Schmitt
Trigger
RELAY
HF AC to
DC
Conversion
TEC
OUTPUT
Thermistor
Figure 13: Block diagram of the Power Supply Circuit
ENG 499 CAPSTONE PROJECT REPORT
29
5.2 Power Supply Specification
The selected design of power supply has an input voltage ( VI ) range from
176Vac to 265Vac at a frequency of 50Hz. The output voltage ( VI ) is 24V and output
current ( VO ) is 13A. The output power ( P ) is 312W with a
o
switching frequency
( f ) of 200 kHz. The design has a target full load efficiency of 90% from mains to
s
output. Figure 14 in the following page shows the schematic diagram of the 300W
power supply.
Figure 14: Schematic Diagram of 300W Power Supply
A typical SMPS has the controller situated at the primary side of the
transformer. The output voltages to be controlled will be located on the secondary
side. Normally the voltage feedback is given to the primary controller with the help of
a transformer/opt coupler. But in the chosen design for this project the SMPS works
differently. An asymmetrical half bridge rectifier forward converter with the
controller IC is located on the secondary side of the circuit. The controller IC in the
ENG 499 CAPSTONE PROJECT REPORT
30
secondary side requires a DIAC (diode for alternating current) based start-up
sequence.
5.2.1 Circuit and PCB layout
The circuit taken form STMicroelectronics was redrawn in a trial version of
ALTIUM electronics design software. The drawing is attached in Appendix C, Figure
C-1.
The circuit was drawn accurately with all the components as specified in
manufactures application note. The circuit was then converted to netlist. The next
step after schematic circuit was to create the PCB layout before printing the circuit
board. The overall layout design guidelines with planes, layers and track were
followed while routing the PCB. The layout can be found in Appendix C, Figure C-2.
The drawn PCB layout was then outsourced to a local company (Fortune Box
Pte Ltd) for printing the circuit board. The following requirements were requested to
the company when printing the circuit board.
1. The board was double layered.
2. The amount of copper used was at least 2 oZ per sqr ft
3. Vertical Interconnect access (Vias) were finished with metalized holes.
4. Top overlay was printed in non conducting material. (.i.e. not using copper)
5. Solder masks were defined and built in.
6. The thickness for the PCB board was 1mm
7. The Pads were covered with stannum (lead + alloy).
Figure 15 shows the top and bottom side of the printed circuit board before soldering
the components.
ENG 499 CAPSTONE PROJECT REPORT
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Figure 15: PCB top and bottom before soldering the components
5.1.2 Circuit Assembly and Sections
Most of the components required for the circuit were bought locally from
Simlim (Singapore). Those items which were not found in the local market were
purchased through RS components or Farnell who are the two major online electronic
component traders. Few items shipped from overseas (China) includes Magnetics
77930A7 Core for the output toroid inductor and L5991A IC the controller .Figure 16
below shows PCB after soldering all the components.
ENG 499 CAPSTONE PROJECT REPORT
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Figure 16: PCB board after soldering all the components
A list of individual items purchased for the circuit assembly is attached in
Appendix D. The whole circuit could be divided into a few segments namely the start
up circuit, gate driver and the MOSFETs, current sense, power transformer and output
inductors, Input and output capacitors.
As mentioned earlier the controller (L5991A IC) located in on the secondary
circuit or secondary side of the power transformer. Therefore a startup circuit is
necessary for the system activation. As soon as the controller IC wakes up it generates
a pulse width modulation signal and it enables the start up circuit. The DIAC sends a
train of controlled pulses to the low side drive section. The second secondary gate
driver transformer energies the floating drive section. The DIAC circuit is connected
to the secondary of the pulse transformer. Figure E-12 (Appendix E) and Figure 17
shows the start-up circuit.
ENG 499 CAPSTONE PROJECT REPORT
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Figure 17: Start up circuit
The pulse transformer (Murata 77208C, Appendix G) is a tiny transformer
designed to ensure the isolation safety requirements and helps to obtain fast switching
times. The pulse from the IC goes to the primary of the pulse transformer, but the
DIAC circuit is connected to the secondary. The transformer has a turns ratio of 1:1:1.
The two MOSFETs are driven by them. Figure E-13 (Appendix E) shows pulse
transformer with two MOSFETs.
The switching MOSFETs (STW14NB50) in the main circuit is shown in
Figure 18. A two switch topology was used in the circuit.
Figure 18: Switching MOSFETs
ENG 499 CAPSTONE PROJECT REPORT
34
As the output current is 13A continuous, two current sense transformers had
been used. CPIN2 and CPIN3 in the above Figure 18. One is sensing the current
flowing into BYV52, when the two MOSFETs are turned ON. Another one is sensing
the current through D5.
Power transformer and output inductor were wound using the specified turn’s
ratio. The power transformer transport energy from the primary to secondary with no
storage. The core selected for the transformer was ETD39 in 3F3 material. The
numbers of primary turns used were 32, and secondary turns were 10. The diameter of
wire chosen was 0.36mm. The windings on the transformer were interleaved, which
means the first half of primary with one layer of 16 turns, the secondary layer with 10
turns and second half of primary with another layer of 16 turns. Figure 19 shows the
wound power transformer for the circuit.
Figure 19: Power Transformer
The output inductor was made using a core 77930(Magnetics). The inductor
has to assure the requested value at a maximum load current. The number of turns
was therefore calculated by the designer taking into account the roll-off of the initial
permeability. The no of turns for the inductor were 24. It was also wound with an
auxiliary winding of 9 turns which gives the necessary supply to L5991A IC. The
output inductor is labeled in the earlier Figure 16.
There are two main input capacitors and three major output capacitor for this
circuit. The input capacitors were for filtering DC. They had to be selected based on
distributing the requested maximum power output at a minimum mains value.
The
ripple voltage is accepted at 100Hz. The two selected input capacitors had a value of
220uf. The output capacitor values were chosen by the circuit designer on the basis of
output voltage ripple requirement. The ripple was due to equivalent series resistance
ENG 499 CAPSTONE PROJECT REPORT
35
(ESR). Three capacitors parallel connected with a value of 1000uF had been used as
the output capacitors.
5.3 Voltage Regulator and Temperature Control Circuit
The voltage regulator circuit and the temperature control circuit (Schmitt
trigger) were the two additional circuits incorporated into the power supply circuit
board. Please refer Figure 20 which shows the adjustable voltage regulator circuit and
Schmitt trigger circuit.
It was designed with the intention of controlling the
temperature of the TEC if needed.
A voltage regulator circuit using LM350AT was connected to the output of the
24V power supply. LM350 is an adjustable 3- terminal positive voltage regulator
capable of supplying excess of 3A over an output range of 1.2V to 25V. When the
regulator circuit was connected it is expected to get a 17V which drives the Schmitt
trigger circuit. R49 and RP3 are the resistors for calibration. R93 has to be adjusted in
such a way as to turn off the relay when the temperature is at the required value. It
was done experimentally through trial and error by continuously monitoring the
desired output temperature and adjusting the value of RP3. R49 has been set currently
to work with a 1 degree hysteresis, and if it causers fluctuation (fast on and off) then a
larger value for R49 can be used. It was set to 500K.
Figure 20: LM350AT (1.2V-25V) Adjustable regulator and Schmitt trigger circuit
ENG 499 CAPSTONE PROJECT REPORT
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Header pin 3 and 4 was connected to the thermistor. Header pin 1 and 2 connected to
a relay that turns on or off the TEC connection. Figure E-14 (Appendix E) shows the
Schmitt trigger circuit in the main board.
ENG 499 CAPSTONE PROJECT REPORT
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Chapter 6: Results and Discussions
6.1 Experimental results of the TEC fan
Temperature readings were performed on the cooling fan at certain conditions.
Both surface temperature and air temperature at different sections on the assembly
were made as the part of testing the product. The measurements were performed using
a handheld digital thermometer (DT 305, TCL).
The first measurements were done without the clips (For clips refer to Figure 10,
item no. 6) installed on the cooling assembly. The temperature measurements were
done during an ambient temperature of 31.2 ° C . Surface temperature on the hot and
cold side heat sinks and air temperature at the cooling fan outlet were monitored for
about 40mins. Figure 21 shows the plotted graph of Temperature against time.
Figure 21: Temperature versus time (when the clips were not installed)
ENG 499 CAPSTONE PROJECT REPORT
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The least temperature of the air obtained at the cooling fan outlet was 28.3 °C ,
which was only 3 °C difference from ambient. The numbers of TECs used were four.
A suitable power supply of 10A and 24V were used to run the TECs. Table F-1 in
Appendix F shows the temperature readings measured.
Based on the first testing results some modifications were done to the cooling
system to improve the coldness of air coming out from the outlet. The whole
assembly of TECs, hot side and cold side heats inks were tighten together with clips.
The no. of TECs and power input to the TECs followed the initial testing
arrangement. The cooling system was monitored for 30mins and temperature
measurements were taken every 5 minutes at an ambient temperature of 31.5 °C .
Temperature readings from the cooling system outlet were also measured. Figure 22
below shows the graph plotted.
Figure 22: Temperature versus time (with clips)
ENG 499 CAPSTONE PROJECT REPORT
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The response obtained after the experiments were striking. It has been noted
that the temperature at the outlet was 25.1 °C , which was a drop of 6.4 °C . So it had
been concluded that while installing tight clips on the assembly will promote greater
heat transfer. Table F-2 in Appendix F shows the temperature measurements taken.
Based on the calculated cooling power in Section 4.2, it has been decided use
six TECs with a suitable power supply for the further testing of the cooling system.
The TEC arrangement was also discussed in the earlier section 4.2. The total required
current and voltage for 6 TECs for the arrangement was 24V and 12A. Since there
were 3 parallel groups of 2 TECs in series, each module would require 12V and can
draw up to a maximum current of 4A. The TECs operates at 40% to 80% of the TEC
maximum performance. The maximum voltage of a TEC was 15.4V. Therefore it was
decided to examine the cooling system at lower the voltage so as to verify any
improvements in temperature readings and to find the best operating voltage of
system. Figure 23 shows the temperature when different voltages are fed to the
cooling system. An adjustable 360W (24V, 15A) power supply was used for the
testing. Different voltages were supplied ranging from 25V to 20V.
Figure 23: Temperature at the outlet versus Voltage
ENG 499 CAPSTONE PROJECT REPORT
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Based on the results it was noted that when supplied with 20V the TECs the
cooling was more effective. The temperature measured was 22.8 °C at 20V supply at
a room temperature of 30.5 °C . Table F-3 in Appendix F shows the measured
temperatures at various voltages. All the future testing was adjusted to 20V since it
gave the best cooling.
The time required to achieve the expected temperature at the cooling fan outlet
was also measured. Readings from thermometer at every 10s were taken after turning
on the TECs. It had been obtained from the results that within 3 minutes the fan
achieved a temperature of 23 °C . It was tested at an ambient temperature of 30 °C .
Figure 24 shows the response of the cooling fan. Table F-4 (Appendix F) shows the
readings taken.
Figure 24: Temperature at outlet
ENG 499 CAPSTONE PROJECT REPORT
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Temperature response at the center of hot side heat sink was also plotted after
turning the TEC on. Figure 25 shows the plotted graph. After 2 minutes the hot side
heat sink temperature stabilizes at about 47 °C . Table F-5 (Appendix F) shows the
readings taken.
Figure 25: Temperature at hotside of heat sink
Testing of the final cooling assembly was done by supplying a power of 360W
(24V and 15A) for 6 TECs. The assembly of the TECs was as discussed in the earlier
Section 4.2. The voltage was adjusted down to 20V since it had already given
maximum cooling during the earlier testing. During the final testing the TEC was
turned on and monitored for half an hour. Surface temperature of all the four cold side
heat sinks, front, middle and rear sections of the long hot side heat sink
were
measured. Temperature measurements at the outlet of the cooling fan as well as 5 cm
away from the outlet were also performed. It had been observed that the TEC cooling
fan bring down the ambient temperature of 30 °C to 22.8 °C . Figure 26 below shows
ENG 499 CAPSTONE PROJECT REPORT
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the graph plotted on the temperature readings against time. The values recorded are
attached in Table F-6(Appendix F).
Figure 26: Temperature measurements on the cooling assembly
6.1.1 Problems faced and solution (Cooling assembly)
During the initial stages of assembling the cooling system finding a suitable
hot side heat sink was an issue. The calculated thermal resistance of the hot side heat
sink did not match with selected heat sink which was dimensionally apt for the
cooling assembly. The corrective action was done by installing 2 fans on the hot side
heat sink to cool it down.
ENG 499 CAPSTONE PROJECT REPORT
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The blower fan which was initially selected had less air flow was not strong
enough to produce a reasonable amount of air at the cooling outlet. Therefore the
blower fan’s power was recalculated as discussed earlier in section 4.4. A new blower
fan was chosen which was of higher power which was in line the calculated values.
The whole cooling system assembly was bulky and heavy. In order not to
reduce the weight it had been decided to use plain cardboard sheets to enclose the
assembly, rather than using glass or wooden box.
6.2 Testing, Troubleshooting and Problems Encountered.
The first round of testing of the power supply board was carried out by
checking the rectified output from the AC line. It had been obtained as 327V DC as
shown in Figure 27 below.
Figure 27: Rectified output from the AC line
There was a rectified DC in the primary but no voltage was obtained in
secondary. On further point by point testing it was found that there was short in the
PCB, which occurred due to the printing error by the supplier. The problem had been
solved by using a knife to cut the connection part between two short circuit pins. It
was done together with a soldering gun.
It was decided to check the waveform in an oscilloscope to check the
switching of MOSFETs. While connecting up the oscilloscopes the power in the room
was tripped due to a ground loop formed by the scope probe. It was resulted when two
separate ground paths are tied together at two points. When the ground lead of the
ENG 499 CAPSTONE PROJECT REPORT
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scope probe was connected to the circuit board which was grounded resulted in the
ground loop. Please refer Figure 28 for the illustration. A voltage potential was
developed in the probe ground path, resulted from circulating current acting on the
impedance within the path.
Figure 28: Ground loop formed by the scope probe
A solution for the ground looping was to use an isolation transformer between
the AC mains and the circuit board before further testing. Figure 29 shows the
isolation transformer used for troubleshooting the circuit.
Figure 29: Isolation transformer
It had been identified that there was always a short occurring at the gate of the
Switching MOSFETs. On brainstorming it was found that the body of the MOSFET
ENG 499 CAPSTONE PROJECT REPORT
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was short through the heat sink attached to it. The solution was to use mica spacers
(Figure 30) to provide insulation between heat sink and MOSFET.
Figure 30: Mica Spacer
On further analysis a major error in the parent design (ST Microelectronics)
was spotted. Vcc to the controller IC (L5991A) had not been connected with respect to
the ground. When the voltage was measured as per the original circuit design at the IC
it was found as 0.1mV. When a ground reference was added in the circuit
subsequently resulted a voltage of 18 V at the IC.
The MOSFET waveform was checked using an oscilloscope and resulted as in
Figure 31 below. Form the waveform it was understood that proper switching of
MOSFET was not taking place.
Figure 31: Switching MOSFET wave form on oscilloscope
After getting the above results a check on the DIAC circuit wad done to ensure
that the circuit was sending pulses to the pulse transformer which enables switching.
Figure 32(a and b) below shows the DIAC (DB3) pulses, which provides give voltage
close to 30 V. The DIAC itself requires a voltage of 27V – 33V for its operation.
Therefore the amplitude was found low for the startup circuit.
ENG 499 CAPSTONE PROJECT REPORT
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Figure 32(a): DIAC pulses
Figure 32(b): DIAC pulses shown on oscilloscope
When the output at the IC was tested, it only showed an output of 2V. The output
waveform of the IC had not enough amplitude and pulse width. A minimum of 10V is
required for the IC to operate. Therefore an external voltage was supplied to the IC to
at the pin 8 and 9 with respect to the secondary ground (pin 11 and 12). The output at
the IC is shown below in Figure 33. The output of the circuit was connected with a
bulb as a load. It was able to turn on the bulb, but the voltage received at the output
was not as expected.
Figure 33: Output at IC on oscilloscope
ENG 499 CAPSTONE PROJECT REPORT
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The voltage and output current received from the power supply was not
enough to drive the TECs. Therefore the temperature control circuit was calibrated
using a separate DC power supply, which was used to test and run the Cooling
system.
ENG 499 CAPSTONE PROJECT REPORT
48
Chapter 7: Conclusions and Further Work
7.1 Conclusions
A Thermoelectric cooling fan prototype was designed and built which can be
used for personal cooling. Six TECs were used for achieving the cooling with a DC
power supply. A conventional axial fan of 35W was used to blow the air to the
cooling module. It had been shown from testing results that the cooling system is
capable of cooling the air .TEC cooling fan designed was able to cool an ambient air
temperature from 30 °C to 22.8 °C . Cooling stabilises within three minutes once the
fan is turned ON. The system can attain a temperature difference of set target which
was 7 °C . Accomplishing the set target establish the success of the project.
A power supply circuit with temperature control circuit was designed and
fabricated for the cooling system. TECs were not powered using the fabricated power
supply considering maximum performance for the cooling system and less current
obtained from the power supply.
Most of the items selected in the project were compromised on budget .A total
of SGD 1033 was spend for the entire project development which includes the
electrical, electronics & mechanical sections. A cost analysis segment is attached in
Appendix D.
All the components in the project had been tested individually and the results
were found to be positive. This was the ultimate result of many a months hard work.
7.2 Further Work
The prototype can be made compact by selecting as single TEC of higher
power (.i.e. of 200W or more). It can be done by choosing a better cold side heat sink
that has twisted channels or pipes for circulating the air for a longer time. As an
alternative for normal axial fan used in this project, if a blower fans is selected, the
cooling system would provide better airflow.
ENG 499 CAPSTONE PROJECT REPORT
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Well-known TEC brands (.i.e. Melcor, FerroTEC etc)
must be chosen if
there is only one high power TEC selected for the cooling system. Bigger hot side
heat sink has to be selected accurately based its calculated thermal resistances for best
cooling efficiency. With a single TEC, one hot side and a cold side heat sink a smaller
personal TEC cooler which gives comfort can be fabricated.
Both the mechanical part (sizing and designing a cooling system) and
electronics sections (designing and fabrication of power supply with temperature
controller) in this project can be two different projects of its own. Designing a
suitable power supply with an apt temperature controller can be a major project.
By changing the airflow and some mechanical or electronics section
modification, the TEC cooling fan can be used for heating applications.
ENG 499 CAPSTONE PROJECT REPORT
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Chapter 8: Critical Review and Reflections
When I first got my project, frankly speaking, I had only a scant idea of how
to proceed further. But the situation had undergone a tremendous change when I
slowly grasped the ins and outs of the project. I am fully aware of the fact that a
project preparation is a Herculean task. I had to chalk out a programmed schedule and
I had to thoroughly adhere to within the timeframe. Since I had to combine my job
and study simultaneously, time management was of utmost importance. In fact I had
undertaken a lot of research work .I wasted no time in scanning internet and any other
sources of materials available from any quarters.
The first thing I had done was to collect all available materials from different
sources such as internet books, IEEE journals etc. I continued reading and
assimilating ideas from other relevant sources also. My Guide was kind enough to
share his valuable ideas. I actually reviewed and recapitulated the skills needed to
accomplish the project.
I had set apart much of my available free time reading, sourcing components,
testing and trouble shooting relating to the project. Altogether I spent a year to fulfil
the task as it was a hard nut to crack in many modules. I strongly feel that doing
projects really need an iron will, strong motivation, strict self-discipline and incessant
perseverance.
This project has been a challenging experience as far as I am concerned. It has
given me an opportunity to get more exposure not only in the fields of electrical and
electronics but also mechanical fields. I can unhesitatingly say that I have acquired
proper skills of the power of analysis, logical reasoning and skills in their true
perspective. Moreover this innovative aspect of designing a product relating to the
project really inspired me.
During the course of evolution of the project many facets of electronic,
electrical and mechanical matters were referred to and executed. This has been both
rewarding and educative. I had found enough chance to be familiar with the nuances
of such areas. I think it is an asset.
ENG 499 CAPSTONE PROJECT REPORT
51
Time constrain was major factor as far as part-time engineering student is
concerned. I even had other modules under-going during the progress of this project.
The situation worsened when you had a project of mechanical and electrical sections.
The designing of the TEC fan and the design of the power supply with temperature
control can be two different projects of its own as discussed earlier.
In the ultimate analysis I have assimilated much knowledge and experience
from this project due to its broad spectrum of multifarious engineering nature. I have
acquired problem solving skills which cannot be underestimated. The project has
considerably enhanced my executive skills also. The evolution of engineering ideas
and fundamental theory into a practical product enhanced me as an engineer. I
emphatically feel that the knowledge I gained from this project will greatly help me in
my future career. I may also contribute this knowledge for the welfare of country, if
necessary.
ENG 499 CAPSTONE PROJECT REPORT
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REFERENCES
Bartlett, S & Sukuse L, 2007, Design and build an air conditioned helmet using
thermoelectric devices, Final Year Project, University of Adelaide.
Buist, RJ & Streitwieser, GD March 16-18,1988, The thermoelectricly cooled helmet,
The Seventeenth International Thermoelectric Conference, Arlington, Texas.
Bulat, L & Nekhoroshev, Y 2003, Thermoelectric cooling-heating unit for
thermostatic body of pickup refrigerated trucks, 22nd international conference on
thermoelectrics.
Harrington, SS 2009, Thermoelectric air cooling device, Patent Application
Publication, US Patent Number 5623828.
Harvie, MR 2005, Personal cooling and heating system, Patent Application
Publication, US Patent Number 6915641.
Hyeung,SC, Sangkook, Y & Kwang-il, W 2007, Development of a temperaturecontrolled car-seat system utilizing thermoelectric device, Applied Thermal
Engineering, pp 2841-2849.
Koetzsch, J & Madden, M 2009, Thermoelectric cooling for industrial enclosures,
Rittal White Paper 304, pp 1- 6.
Larid 2009, Thermoelectric AssembliModules for Industrial Applications, Application
Note, Larid Technologies.
Lauwers, W & Angleo, SD 2009, The Cooling VestEvaporative Cooling, Final Year
Degree Project, Worcester polytechnic institute.
Marlow Industries, Thermoelectric Cooling systems Design Guide, pp -11, Dallas,
Texas.
Melcor 2010, Thermoelectric Handbook, Laird Technologies.
McStravick, M et.al 2009, Medical travel pack with cooling System, Patent
Application Publication, US Patent Number 49845A1.
Rowe, DM & Bhandari CM 2000, Modern thermoelectrics. Reston Publishing, USA.
Rowe, DM 1995, CRC handbook of thermoelectrics. Boca Raton, FL: CRC Press.
Rowe, DM 2006, Thermoelectrics Handbook: Macro to Nano. Boca Raton, FL:
CRCPress.
ST Microelectronics 2004, 300W Secondary Controlled Two switch forward
converter with L5991A, AN1621 Application Note.
ENG 499 CAPSTONE PROJECT REPORT
53
Tan, FL & Fok, SC 2008, Methodology on sizing and selecting thermoelectric cooler
from different TEC manufacturers on cooling system design. Energy conversion and
management 49,pp 1715-1723
Tektronix 1996, Differential Oscilloscope Measurements, 51W-10540-1Technical
Note, pp 1-4, USA.
Yunus, AC & Afshin, JG 2011, Heat and mass transfer: fundamentals &
applications .4th Edition, McGraw-Hill, New York.
Yunus, AC, Robert, HT & John, MC 2008, Fundamentals of Thermal-Fluid
Sciences. 3rd Edition, McGraw-Hill, New York.
Bioserve space technologies 2003 Cooling fans with heat exchangers
http://www.colorado.edu/engineering/ASEN/asen5519/09fans-heat.htm,
Accessed 05 Sep 2010.
Craig Forsythe 2009, Craig’s thermostat circuits,
http://www.craig.copperleife.com/tech/thermo/ Accessed 15 May 2010
Ferro TEC 2001-2010, Technical reference guide, Ferrotec (USA) Corporation
http://www.ferrotec.com/technology/thermoelectric/thermalRef09/,
Accessed 12 Oct 2010.
National Semiconductor Corporation 2010, 3-Amp Adjustable Regulator
http://www.national.com/mpf/LM/LM350.html#Overview, Accessed 28 Aug 2010
Kryotherm 2007 ‘Kryotherm: Engineering & Production
Firm’http://www.kryotherm.ru. Accessed 01 Sep 2010.
TEC Mirco systems GMBH 2010, Thermoelectric cooler basics’
http://www.tec-microsystems.com/EN/Intro_Thermoelectric_Coolers.html,
Accessed 16 Sep 2010.
TE Techology Inc 2010, TEC Advantages
http://www.tetech.com/FAQ-Technical-Information.html, Accessed 06 April 2010.
ENG 499 CAPSTONE PROJECT REPORT
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Appendix A
Solid work drawings
Each of the thermoelectric cooling fan’s components was modeled in solid
works for the purposes of properly dimensioning the components as well as the
complete assembly. Some of the components were available readily in the solid
works library.
Figure A-1: Top view of the Thermoelectric cooling fan
Figure A-2 in the following page shows the view of the prototype from the
front, where ambient air flows into the assembly.
ENG 499 CAPSTONE PROJECT REPORT
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Appendix A
(cont’d)
Solid work drawings (cont’d)
Figure A-2: Front view of the Thermoelectric cooling fan
Figure A-3 below shows the view of the prototype from the rear where cool air
flows out from the assembly.
Figure A-3: Rear view of the Thermoelectric cooling fan
ENG 499 CAPSTONE PROJECT REPORT
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Appendix A
(cont’d)
Solid work drawings (cont’d)
Figure A-4 below is the side view of the assembly. The TECs can be seen
between the hot side and cold side heat sinks.
Figure A-4: Side view of the Thermoelectric cooling fan
The exploded view of the whole assembly is shown in the below in Figure
A.5, where all the parts were dismantled.
Figure A.5: Exploded view of the Thermoelectric cooling fan.
ENG 499 CAPSTONE PROJECT REPORT
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Appendix B
Calculations
All calculations used in this project related to the cooling load, selection of
heat sinks, selection of fans, pressure drop calculations, surface area needed to cool
the air etc can be found in Appendix B.
B.1: Cooling load
Q
The amount of heat load to be absorbed by the cold junction has to be
c
calculated before the selection of TEC.
Q  m C 
c
p
m  Q
  1.164 kg / m3 ( At 30 C )
Q V  A
A W H
0.0796m  0.068m
 0.0054128m 2
V  5m / s 2
Q  0.0054128m 2  5m / s 2
 0.02706m3 / s
m  1.164 kg / m3  0.02706m3 / s
 0.0315 kg / s
C  1007 J / kgK ( At 30 C )
p
  in - out
 30C - 23C  7 
 0.0315 kg / s 1007 J / kg .K  7 K
Q
c
Q  222.06  222 W
c
Q was calculated by adding the electrical power input and the cooling load.
h
ENG 499 CAPSTONE PROJECT REPORT
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Appendix B
(cont’d)
Calculations (cont’d)
P
 300 W
e
Q  222  P
h
e
 222 W  300 W  522 W
COP 
Q
c
P
e

222 W
 0.74
300 W
This was not the actual COP of the system. It can be higher, as the power input
designed is higher than the calculated Q . A higher power input for TECs were
c
selected in the project. The system was designed with a higher power input.
Therefore the actual COP can be even higher.
B.2: Thermal Resistance of the Hot side Heat Sink.
Hot side heat sink has to be selected based on its Thermal resistance. The
thermal resistance of the hot side heat sink is calculated below.
(T - T )
h

R
t
Q  522W (Q  P )
h
c
e
T  30C

T  50C
h
(T - T )
h
  20 K
R 
t
Q
522 W
h
 0.038 K / W
Q 
h
Thermal Resistance of the selected heat sink is calculated as follows. The resistances
acting on the selected heat sink (Appendix E, Figure E–7) can be divided into two.
They are the resistance offered by the base ( Rb ) / unfinned area and the resistance
offered by the fins ( Rf )/ finned area.
ENG 499 CAPSTONE PROJECT REPORT
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Appendix B
(cont’d)
Calculations (cont’d)
Since both of these resistances are acting in parallel, total resistance will be equal to,
1
1
1


R
R
R
t
b
f
Calculation of R :b
Area A , is the net base area or the unfinned area through which the heat is flowing.
b
Width of the heat sink
= 0.3m
Length of the base
= 0.1m
Thickness of each fin
= 0.002m
Total space occupied by 10 fins
= 0.002m x 10 = 0.02m
Length of Remaining base w/o fins = 0.1m – 0.02m = 0.08m
Width of the heat sink
= 0.3m
1
R 
b
hA
b
A  0.08  0.3  0.024m 2
b
h  100W / m 2 K
1
R 
 0.41666 K / W
2
b
100W / m K 0.024m 2
Calculation of R
A
A
fin
fin
f
is the area of the 1 fin.
 2wL
c
Where w is the width of the fin and the L is the length along with its thickness.
c
L  Lt / 2
c
Width ( w ) of the fin = 0.3m, which also same as the width of heat sink
Length (L) of the each fin = 0.022m
ENG 499 CAPSTONE PROJECT REPORT
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Appendix B
(cont’d)
Calculations (cont’d)
R
f

Afin 
L 
c

Afin 
1
hA
fin
2 wL
c
t
0.02m
L   .1m 
2
2
0.11m
2  .3m  0.11m
 0.066m 2
h  100 W / m 2 K
1
Rf 
2
100 W / m K  0.066m 2
 0.151 K/W
There are 10 identical fins in parallel, N = 10
R
f 0.151
Therefore Net R 

 0.0151K / W
f
N
10
Total resistance
1
1
1


R
R
Net R
t
b
f
1
1


0.41666 K / W
0.0151 K / W
R  0.0145K / W
t
The thermal resistance of the selected heat sink was lower than the required resistance
for the system. This may cause the heat sink to overheat, but bigger cooling fans were
installed to overcome it.
ENG 499 CAPSTONE PROJECT REPORT
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Appendix B
(cont’d)
Calculations (cont’d)
B.3 Power of the blower fan.
The power of the fan will be equal to the product of total pressure drop ( P )
t
and volume flow rate. The total pressure drop will be the sum of pressure drop in
cold side heat sink channel(rectangular channel) and the circular duct.
To calculate the pressure drop using Darcy Law, the equation is as follows:
The pressure drop = 0.5  (
fL
)    v2
D
Pressure drop in the circular duct P :c
For the circular duct, Darcy friction factor is value is taken as 0.03 for
f  0.03
L  0.085m
D  0.14m, r  0.07
  1.164 kg / m3 ( At 30 C )
Q  vA
v 
Q
A
Q  0.02706m3 / s
A   r2
 3.14  0.07 2
 0.0153m 2
0.02706m3 / s
v 
0.0153m 2
 1.77 m / s
fL
P
0.5 
   v2
c
D
0.03  0.085m
 0.5 
 1.164kg / m3  1.77 2 m / s
0.16m
 0.029 N / m 2
ENG 499 CAPSTONE PROJECT REPORT
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Appendix B
(cont’d)
Calculations (cont’d)
Pressure drop in a rectangular channel and heat sink ( P )
r
For calculating the pressured drop in a rectangular channel of the heat sink, D
is taken as 0.5*W, where W is the spacing between the channel. A total of 20 fins (i.e
19 gaps/channels) with each having a thickness or W of 0.003m. For Calculating
pressure drop across the rectangular the cross sectional area of the heat sink (W x H)
had to be considered. . Height of the heat sink = 0.068m & width =0.0796m
D  0.5 W
 0.5  0.003m
 0.0015m
f  0.03
L  0.252m
H  0.068m
W  0.0796m (heatsink width)
  1.164 kg / m3 ( At 30 C )
Q
A
Q  0.02706m3 / s (From Appendix B.1)
v
A  WH
 0.0796m  0.068m
 0.0054128m 2
0.02706m3 / s
0.0054128m 2
 5m / s
v
fL
P
0.5     v 2
r channel 
D
0.03  0.252m
0.5 
1.164kg / m3  52 m / s

0.0015mm
 73.3N/m 2
Since there are a total of 19 channels, the total pressure drop across the heat sinks or
rectangular duct will be equal to 19  pressure drop in 1 channel.
ENG 499 CAPSTONE PROJECT REPORT
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Appendix B
(cont’d)
Calculations (cont’d)
Net P  N  P
r
r channel
=19  73.3N/m 2
=1393.3 N/m2
Total pressure drop P = P + P
c r
t
= 0.029 N/m 2 + 1393.3 N/m 2
= 1393.33 N/m2
Power of the fan
= Total pressure drop  volume flow rate
Volume flow rate
= 0.02706m3 / s
= 1393.33 N/m2  0.02595711 m3 / s
= 36 W
Power
The Blower fan model GH14045HA was of 0.18A and the power of the fan
was 35W. Hence from the calculation it proved that the selection of the fan was
acceptable.
B.4: Surface area needed to cool the air.
From the earlier section of Appendix B.1 the value of Q was already been
c
calculate. The calculations shown below computes the surface area needed to cool the
air.
ENG 499 CAPSTONE PROJECT REPORT
64
Appendix B
(cont’d)
Calculations (cont’d)
Q  m C   222 W
c
p
Q  hA
c
Q
A c
h
h  100 W / m 2 K
  T - Tc
in  out
2
30C  23C

 26.5C
2
Tc  15C
T
  26.5C  15C  11.5 K
222 W
100 W / m 2 K  11.5 K
 0.193m 2
A 
ENG 499 CAPSTONE PROJECT REPORT
65
Appendix C
Power Supply Circuit
Figure C-1: Schematic of the power supply circuit
ENG 499 CAPSTONE PROJECT REPORT
66
Appendix C
(cont’d)
Power Supply Circuit (cont’d)
Figure C-2: PCB layout of the power supply circuit
ENG 499 CAPSTONE PROJECT REPORT
67
Appendix D
Cost analysis
Table D.1 summarizes each of the costs associated with this project. It can be
divided in to three sections. First one was the cost incurred for the Electrical and
Electronics part, which was to make the SMPS power supply. Second one was to
fabricate the cooling fan assembly and the third was for testing. Where possible,
items required for this project have been sourced for an amount less than the retail
cost of the item. Many components required for the project were lying around the
home and some others where borrowed from the project supervisor and friends.
Table D-1: Cost Analysis
UNIT
PRICE
ITEMS DESCRIPTION
QUANTITY AMOUNT
ELECTRICAL AND ELECTRONICS
STW15NB50, MOSFETS
3 PIN PLUG
COPPER WIRE, 100/0,40
VOLTAGE REGULATOR, LM350AT
CURRENT SENSE, CST306- 1A
ECORE KIT, ETD39/FN44(V)
CAPACITOR, 2.2UF
MINI PWR RELAY, 12V DC
ISOLATION TRANSFORMER, 50VA 0 230V
THERMISTOR NTC
PULSE TRANSFORMER, MURATA
HEAT SINKS, CIRCUIT
SPACER FOR MOSFETS
DIODE, DFD 30 TL
HEAT SINK, HS 211- 50
DIODE, BYV52-200
DIODE LN 4007
INDUCTOR, MIX 10A
1 EC CASK
3 WAY EXT CORD
EMI FILTER 6A
ENG 499 CAPSTONE PROJECT REPORT
$6.00
$1.50
$9.00
$6.15
$7.50
$15.70
$0.93
$3.56
$55.90
6
1
1
1
2
1
5
1
$5.66
$21.01
$1.50
$0.10
$1.00
$1.70
$12.00
$0.50
$15.00
$4.50
$19.00
$17.00
2
1
2
4
4
1
1
4
1
1
1
1
1
$36.00
$1.50
$9.00
$6.15
$15.00
$15.70
$4.65
$3.56
$55.90
$11.32
$21.01
$3.00
$0.40
$4.00
$1.70
$12.00
$2.00
$15.00
$4.50
$19.00
$17.00
68
Table D-1: Cost Analysis (cont’d)
UNIT
PRICE
ITEMS DESCRIPTION
QUANTITY AMOUNT
ELECTRICAL AND ELECTRONICS
FUSE HOLDER 30MM
FUSE 8A
FUSE 8A
HEAT SINK, CIRCUIT 2
2 PIN CONNECTOR
TANTALUM CAPACITOR
OPAMP UA 741
BJT
CAPACITOR, BIG 420V
ST PLUG SKT CABLE
RESISTORS
VARIABLE RESISTOR
UA 741
IC SOCKET
ZENER DIODE
ZENER DIODE IN 4148
CAPACITORS
CAPACITORS
RESISTOR 1 W
RESISTOR .5 W
SOLDER
L5991A IC
MAGNECTICS TOROID,77930A7
POTENTIOMETERS, 2K & 100K
STW15NB50, MOSFETS
4 PIN PLUG
$2.20
$0.30
$1.70
$2.50
$1.00
$1.50
$1.00
$0.60
$3.00
$3.00
$0.08
$1.00
$1.00
$0.40
$0.30
$0.30
$0.70
$0.40
$0.20
$0.10
$1.00
$1.15
$1.53
$1.20
$0.50
$200.00
1
2
2
2
3
2
1
1
2
1
48
3
1
6
1
11
2
10
3
1
3
5
3
2
1
1
$2.20
$0.60
$3.40
$5.00
$3.00
$3.00
$1.00
$0.60
$6.00
$3.00
$3.84
$3.00
$1.00
$2.40
$0.30
$3.30
$1.40
$4.00
$0.60
$0.10
$3.00
$5.76
$4.60
$2.40
$0.50
$200.00
1
1
2
1
1
7
6
3
5
$27.00
$30.00
$30.00
$4.20
$8.00
$7.00
$27.00
$3.00
$40.00
MECHANICAL
BLACK HOTSIDE HEAT SINK
AC FAN, BLOWER
FANS, HOT SIDE
THERMAL COMPOUND, ANABOND
GLUE GUN
GLUE STICK
CLIPS
SCREWS/BOLT & NUTS
HEAT SINK - AL
ENG 499 CAPSTONE PROJECT REPORT
$27.00
$30.00
$15.00
$4.20
$8.00
$1.00
$4.50
$1.00
$8.00
69
Table D-1: Cost Analysis (cont’d)
UNIT
PRICE
ITEMS DESCRIPTION
QUANTITY AMOUNT
MECHANICAL
WOODEN BOARD
TEC's 12704
SAW
CARDBOARDS
$10.00
$16.00
$7.50
$5.00
1
6
1
2
$10.00
$96.00
$7.50
$10.00
$20.00
$58.00
$1.50
$20.00
1
1
1
1
$20.00
$58.00
$1.50
$20.00
1
1
$23.00
$20.00
TESTING
POWER SUPPLY (24V, 10A)
POWER SUPPLY (24V, 15A)
9 V BATTERY FOR MULTIMETER
DIGITAL HYGRO THERMOMETER
MISCELLENEOUS
SHIPPING CHARGES
WESTERN UNION SERVICE CHARGE
TOTAL
GST
SUB TOTAL
ENG 499 CAPSTONE PROJECT REPORT
$23.00
$20.00
$964.59
$67.52
$1,032.11
70
Appendix E
The prototype and circuit board.
Figure E-1 shows the front–side view of the prototype. It shows the internal
structure of the assembly during the initial construction stage of the prototype.
Figure E-1: Internal assembly of the prototype.
ENG 499 CAPSTONE PROJECT REPORT
71
Appendix E
(cont’d)
The prototype and circuit board. (cont’d)
Figure E-2: Wooden base of the assembly
Figure E-3: Hot air channel
ENG 499 CAPSTONE PROJECT REPORT
72
Appendix E
(cont’d)
The prototype and circuit board. (cont’d)
Figure E-4: One of the cold side heat sinks
Figure E-5: Two TEC1-12704 connected in series
ENG 499 CAPSTONE PROJECT REPORT
73
Appendix E
(cont’d)
The prototype and circuit board. (cont’d)
Figure E-6: Cold side rectangular duct
Figure E-7: Hot side heat sink
ENG 499 CAPSTONE PROJECT REPORT
74
Appendix E
(cont’d)
The prototype and circuit board. (cont’d)
Figure E-8: Blower Fan
Figure E-9: Top view of the assembly
ENG 499 CAPSTONE PROJECT REPORT
75
Appendix E
(cont’d)
The prototype and circuit board. (cont’d)
Figure E-10: Cooling fan outlet
Figure E-11: Side view of the assembly
ENG 499 CAPSTONE PROJECT REPORT
76
Appendix E
(cont’d)
The prototype and circuit board. (cont’d)
Figure E-12: Start up circuit
Figure E-13: Pulse transformer and MOSFET with heat sinks.
ENG 499 CAPSTONE PROJECT REPORT
77
Appendix E
(cont’d)
The prototype and circuit board. (cont’d)
Figure E-14: Schmitt Trigger circuit
ENG 499 CAPSTONE PROJECT REPORT
78
Appendix F
Experimental results
Temperature measurements of the cooling fan with 4 TECs and 240W power
supply were performed as the initial stage testing. The assembly was tested without
the clips fitted. Table F-1 Shows the readings and in the table time is in minutes and
temperature in degree Celsius.
Table F-1: Temperature readings without clips
Temperature
Temperature Temperature Temperature Temperature Temperature
5cm away
Time at cold side at cold side at cold side at cold side at hot side
from the
heat sink 1 heat sink 2 heat sink 3 heat sink 4 heat sink
outlet
0
31.2
31.2
31.2
31.2
31.2
31.2
10
31.5
30.5
29.7
28.0
44.3
28.3
20
31.7
30.9
29.9
29.1
45.0
29.3
30
31.6
30.6
29.8
29.0
45.2
29.4
40
31.6
30.6
29.8
29.0
45.2
29.3
Temperature readings were taken with 3 set of clips installed to hold the
TECs, cold side heat sink and hot side heat sink tightly. The room temperature was
31.5 degree Celsius. Table F-2 shows the measurements taken when clips were
installed.
Table F-2: Temperature readings with clips
Temperature
Temperature Temperature Temperature Temperature Temperature
Outlet
5cm away
Time at cold side at cold side at cold side at cold side at hot side
temperature from the
heat sink 1 heat sink 2 heat sink 3 heat sink 4
heat sink
outlet
0
31.5
31.5
31.5
31.5
31.5
31.5
31.5
5
31.2
30.9
28.1
27.0
52.0
25.5
26.2
10
31.0
30.0
27.9
26.7
50.5
25.5
26.3
15
31.2
30.1
28.1
26.7
52.0
25.6
26.4
20
31.4
29.7
27.8
26.2
51.0
25.7
26.4
25
31.6
29.6
27.6
26.1
50.1
25.6
26.5
30
31.4
29.8
27.8
25.9
51
25.1
26.2
ENG 499 CAPSTONE PROJECT REPORT
79
Appendix F
(cont’d)
Experimental results (cont’d)
The cooling fan assembly was supplied with different range of voltages to find
out the best operating voltage, when 6 TECs were used. The power supply used was
24V-15A, 360W. Table F-3 shows the measurements taken at different voltages.
Table F-3: Temperature readings at different Voltages
Voltage (V)
25
24
23
22
21
20
Temperature at Outlet
24.3
23.4
23.2
23.1
23.0
22.8
Table F-4 shows the decreasing temperature at the outlet when the TECs were
turned on. The ambient temperature measured was 30.5 degree Celsius.
Table F-4: Time required achieving the expected cooling
Time (s)
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
150
160
170
180
190
200
ENG 499 CAPSTONE PROJECT REPORT
Temperature at Outlet
30.5
28.5
27.7
27.2
26.6
26.1
25.7
25.3
25.0
24.6
24.4
24.1
23.9
23.8
23.5
23.3
23.2
23.1
23.0
23.0
23.0
80
Appendix F
(cont’d)
Experimental results (cont’d)
Table F-5 below shows the measured temperature at the center of the hot side
heat sink until it stabilizes.
Table F-5: Temperature at the center of hot side heat sink
Time (s)
Temperature at hot side heat sink
0
10
20
30
40
50
60
70
80
90
100
110
120
130
140
30.5
31.2
33.4
36.3
38.7
40.8
43.0
44.4
45.8
46.9
46.5
46.6
46.7
47.0
47.0
Final testing of TECs for the completed assembly for about 30 mins.
Temperature measured at different locations is shown in Table F-6.
Table F-6: Temperature results of the TEC fan (Final Assembly)
T at 5cm
T at
Time T at cold T at cold T at cold T at cold Outlet(T) from
hotside T at hotside T at hotside
(s) side H1 side H2 side H3 side H4
outlet
H(Front) H(Center)
H(End)
0
30.0
30.0
30.0
30.0
30.0
30.0
30.0
30.0
30.0
5
26.9
25.1
25.6
25.4
25.0
54.4
47.1
40.0
23.4
10
27.0
24.5
24.8
24.3
25.1
55.8
48.2
41.9
22.8
15
27.7
24.2
24.8
24.0
24.2
54.5
47.7
41.3
22.7
20
27.0
24.4
24.2
24.0
24.0
54.7
47.5
41.4
22.8
25
26.9
24.4
24.3
24.0
24.1
54.8
47.1
42.0
22.9
30
27.1
24.5
24.4
22.8
24.0
54.6
47.0
41.3
22.8
ENG 499 CAPSTONE PROJECT REPORT
81
Appendix G
Datasheets
ENG 499 CAPSTONE PROJECT REPORT
82
Appendix G
(cont’d)
Datasheets (cont’d)
TEC1-12704
Qc vs I
Qc Watts
th=50 °C
60
50
40
—ΔT=0
—ΔT=10
—ΔT=20
—ΔT=30
—ΔT=40
—ΔT=50
—ΔT=60
—ΔT=67
30
20
10
0
0
0
0.5
1.0
0.5
1.5
1.0
2.0
1.5
2.5
3.0
2.0
2.5
3.5
4.0 A
3.0
3.5
4.0 A
Vin—Th ΔT=30 °C
30
25
I=4.0A
20
I=3.0A
15
I=2.0A
I=1.0A
10
5
0
-100
-50
0
ENG 499 CAPSTONE PROJECT REPORT
50
100
150
Th °C
83
Appendix G
(cont’d)
I—Vin
Th=50 °C
V
20
ΔT=60
ΔT=50
ΔT=30
ΔT=0
15
10
5
0
0
1
2
3
4A
Vin— I —TC Th=50℃
V
20
15
I=4
I=3
10
5
I=2
I=1
0
-25
-10
5
20
35
50 Tc( °C )
60
75 DT( °C )
Qc — I —D Th=50 °C
Qc(w)
aa60
0
15
30
45
45
30
15
0
1A
ENG 499 CAPSTONE PROJECT REPORT
2A
3A
4A
84
Appendix G
(cont’d)
Datasheets (cont’d)
ENG 499 CAPSTONE PROJECT REPORT
85
Appendix G
(cont’d)
Datasheets (cont’d)
ENG 499 CAPSTONE PROJECT REPORT
86
GLOSSARY
CFC
Chloro fluro carbon
DIAC
Diode for alternating current
MOSFET
Metal oxide semiconductor field effect transistor
PCB
Printed circuit board
SMPS
Switching mode power supply
TE
Thermoelectric
TEC
Thermoelectric cooler
TEM
Thermoelectric module
TEA
Thermoelectric assembly
ENG 499 CAPSTONE PROJECT REPORT
87