2. 2
It is with the sense of great satisfaction and pride that we are
sitting down to pen our project report. On this day, we stand
indebted to Mr. Anand Sir, Lecturer at Government
Polytechnic, Masab Tank, Hyderabad for his valuable
advices, guidance and suggestions through our project work
which played a vital role in carrying out this project
successfully. We are also thankful for his cooperation and
help for successful completion of this project.
We are profoundly thankful to Mr. Venkateshwarlu,
Head of Mechanical department, for his dynamic invaluable
technical guidance and constant encouragement, without
which we couldn’t have completed our project successfully.
In this context we would like to thank all our staff members
in Department of Mechanical engineering, Masab Tank, for
there constant encouragement in carrying out our project
work.
We would like to thank our friends whose constant
doubts and suggestions inspired us throughout the course of
the project.
3. 3
GOVERNMENT POLYTECHNIC, MASAB TANK
Affiliated to SBTET,
ASIFNAGAR, HYDERABAD-500028.
CERTIFICATE
This is to certify that the project entitled, “DESIGN OF MINI COMPRESSOR LESS
PELTIER REFRIGERATOR” is being submitted by
MUDAVATH BABURAM (13001-M-036)
In partial fulfilment for the degree of DIPLOMA IN MECHANICAL ENGINEERING,
Government Polytechnic, Masab tank, Hyderabad-500028, Affiliated to SBTET, is
record of bonafide work carried by him under our supervision.
Mr. Anand A. VENKATESHWARLU
(LECTURER) (HOD, MECHANICAL)
INTERNAL GUIDE
K. RAMULU
EXTERNAL GUIDE (PRINCIPAL)
4. 4
DECLARATION
We hereby declare the results embodied in this dissertation
titled “ DESIGN OF MINI COMPRESSOR LESS
PELTIER REFRIGERATOR” is carried out during the
year 2015-2016 in the practical fulfilment of the award
DIPLOMA from “GOVERNMENT POLYTECHNIC,
MASAB TANK, HYDERABAD”. We have not submitted
the same to any other university or organization for the
award of any other degree.
5. 5
Abstract
we designed and constructed a COMPRESSOR LESS PELTIER
REFRIGERATOR with an interior cooling volume of 3.45 cubic
meters (1.5m x 1.0m x 2.3m). The Peltier refrigerator was
equipped with on/off control which was found to be adequate to
meet the required precision of +/- 15 degrees Celsius put forth in
the project requirements.
One liter of water was placed inside the cooler to test the
performance of the device. We tested the maximum
performance of the device by cooling a sample down to -5
degrees Celsius. Temperature control was also tested by cooling
one liter of water from room temperature down to -5 degrees
Celsius. On/off control was found to give adequate performance
and we met or exceeded all of our project requirements set forth
in the fall semester of 2016.
6. 6
TITLE PAGE
NO.
CHAPTER:1 INTRODUCTION 6
CHAPTER:2 THEORY OF PELTIER
UNIT
Peltier History
Peltier Structure
Peltier theory
Why use TE coolers
Disadvantages
Which industries use TE cooling
and their applications?
Basic Principles
Semiconductor P and N Type
Doping
Thermoelectric materials
Condensation
TE performance
8
CHAPTER:3 MATERIALS USED 26
CHAPTER:4 CONSTRUCTION AND
DESIGN
32
CHAPTER:5 WORKING OF FRIDGE 35
CHAPTER:6 COST ANALYSIS 37
CHAPTER:7 CONCLUSION 39
7. 7
Conventional cooling systems such as those used in
refrigerators utilize a compressor and a working fluid to
transfer heat. Thermal energy is absorbed and released as
the working Fluid undergoes expansion and compression
and changes phase from liquid to vapor and back,
respectively. Semiconductor thermoelectric coolers (also
known as Peltier coolers) offer
Several advantages over conventional systems. They are
entirely solid-state devices, with no moving parts; this
makes them rugged, reliable, and quiet. They use no ozone-
depleting chlorofluorocarbons, potentially offering a more
environmentally responsible alternative to conventional
refrigeration. They can be extremely compact, much more so
than compressor-based systems. Precise temperature
control (< ± 0.1 °C) can be achieved with Peltier coolers.
However, their efficiency is low compared to conventional
refrigerators. Thus, they are used in niche applications
where their unique advantages outweigh their low efficiency.
Although some large-scale applications have been
considered (on submarines and surface vessels), Peltier
coolers are generally used in applications where small size is
needed and the cooling demands are not too great, such as
for cooling electronic components.
8. 8
The objectives of this study is design and develop
a working thermoelectric refrigerator interior cooling
volume of 5L that utilizes the Peltier effect to refrigerate
and maintain a selected temperature from 5 °C to 25 °C.
The design requirements are to cool this volume to
temperature within a time period of 6 hrs. and provide
retention of at least next half an hour. The design
requirement, options available and the final design of
thermoelectric refrigerator for application are
presented
9. 9
Peltier History
Early 19th century scientists, Thomas Seebeck and Jean
Peltier, first discovered
the phenomena that are the basis for found that if you
placed a temperature gradient across the junctions of two
Dissimilar conductors, electrical current would
flow. Peltier, on the other hand, learned that
passing current through two dissimilar electrical
conductors, caused heat to be either emitted or
absorbed at the junction of the materials. It was
only after mid-20th Century advancements in
semiconductor technology, however, that practical
applications for thermoelectric devices became
feasible. With modern techniques,
We can now produce thermos electric efficient solid state
heat-pumping for both cooling and heating; many of these
units can also be
used to generate DC power at reduced efficiency.
New and often elegant uses for thermo-electrics
continue to be developed each day.
10. 10
Peltier structure
A typical thermoelectric module consists of an array of
Bismuth Telluride semiconductor pellets that have been
carrier–either positive or negative–carries the majority of
current. The pairs of
P/N pellets are configured so that they are
connected electrically in series, but thermally in
parallel. Metalized ceramic substrates provide the
platform for the pellets and the small conductive
tabs that connect them.
Peltier Theory
When DC voltage is applied to the module, the
positive and negative charge carriers in the pellet
array absorb heat energy from one substrate surface
and release it to the substrate at the opposite side.
The surface where heat energy is absorbed becomes
cold; the opposite surface where heat energy is
released becomes hot. Reversing the polarity will
result in
Reversed hot and cold sides
11. 11
Why is TE Coolers Used for Cooling?
No moving parts make them very reliable;
approximately 105 hrs of operation at 100 degrees
Celsius, longer for lower temps (Goldsmid,1986).
Ideal when precise temperature control is required.
Ability to lower temperature below ambient.
Heat transport controlled by current input.
Able to operate in any orientation.
Compact size make them useful for applications where
size or weight is a constraint.
Ability to alternate between heating and cooling.
Excellent cooling alternative to vapor compression
coolers for systems that are sensitive to mechanical
vibration.
DISADVANTAGES
Able to dissipate limited amount of heat flux.
Less efficient then VCR system
Relegated to low heat flux applications.
More total heat to remove than without a TEC.
12. 12
Electronic
Medical
Aerospace
Telecommunications
Cooling:
Electronic enclosures
Laser diodes
Laboratory instruments
Temperature baths
Refrigerators
Telecommunications equipment
Temperature control in missiles and space systems
Heat transport ranges vary from a few mill watts to
several thousand watts, however, since the efficiency of
TE devices are low, smaller heat transfer applications
are more practical.
13. 13
When a p type semiconductor (doped with holes)
is used instead, the holes move in a direction opposite
the current flow. The heat is also transported in a
direction opposite the current flow and in the direction
of the holes. Essentially, the charge carriers dictate the
direction of heat flow.
14. 14
Method of Heat Transport
There are several methods which can be employed to
facilitate the transfer of heat from the surface of the
thermoelectric to the surrounding.
Electrons can travel freely in the copper conductors
but not so freely in the semiconductor.
As the electrons leave the copper and enter the hot-
side of the p-type, they must fill a "hole" in order to
move through the p-type. When the electrons fill a
hole, they drop down to a lower energy level and
release heat in the process.
Then, as the electrons move from the p-type into the
copper conductor on the cold side, the electrons are
bumped back to a higher energy level and absorb heat
in the process.
Next, the electrons move freely through the copper
until they reach the cold side of the n-type
semiconductor. When the electrons move into the n-
type, they must bump up an energy level in order to
move through the semiconductor. Heat is absorbed
when this occurs.
Finally, when the electrons leave the hot-side of the n-
type, they can move freely in the copper. They drop
down to a lower energy level and release heat in the
process.
15. 15
To increase heat transport, several p type or n type
thermoelectric(TE) components can be hooked up in
parallel.
However, the device requires low voltage and therefore,
a large current which is too great to be commercially
practical.
The TE components can be put in series but the heat
transport abilities are diminished because the
interconnecting’s between the semiconductors creates
thermal shorting.
16. 16
The most efficient configuration is where a p and n TE
component is put electrically in series but thermally in
parallel . The device to the right is called a couple.
One side is attached to a heat source and the other a
heat sink that convects the heat away.
The side facing the heat source is considered the cold
side and the side facing the heat sink the hot side.
Between the heat generating device and the conductor
must be an electrical insulator to prevent an electrical
short circuit between the module and the heat source.
17. 17
The electrical insulator must also have a high thermal
conductivity so that the temperature gradient between
the source and the conductor is small.
Ceramics like alumina are generally used for this
purpose.
The most common devices use 254 alternating p and n
type TE devices.
The devices can operate at 12-16 V at 4-5 amps. These
values are much more practical for real life operations.
An entire assembly
18. 18
Semiconductor Doping: N Type
N doped semiconductors have an
abundant number of extra electrons to use
as charge carriers. Normally, a group IV
material (like Si) with 4 covalent bonds (4
valence electrons) is bonded with 4 other
Si. To produce an N type semiconductor, Si
material is doped with a Group V metal (P
or As) having 5 valence electrons, so that
an additional electron on the Group V
metal is free to move and are the charge
carriers
19. 19
Semiconductor Doping: P Type
For P type semiconductors, the dopants are
Group III (In, B) which have 3 valence electrons, these
materials need an extra electron for bonding which
creates “holes”. P doped semiconductors are positive
charge carriers. There’s an appearance that a hole is
moving when there is a current applied because an
electron moves to fill a hole, creating a new hole where
the electron was originally. Holes and electrons move
in opposite directions.
20. 20
THERMOELECTRIC MATERIALS
Semiconductors are the optimum choice of material
to sandwich between two metal conductors (copper)
because of the ability to control the semiconductors’
charge carriers, as well as, increase the heat pumping
ability.
The most commonly used semiconductor for
electronics cooling applications is Bi2Te3 because of its
relatively high figure of merit. However, the
performance of this material is still relatively low and
alternate materials are being investigated with possibly
better performance.
Alternative materials include:
Alternating thin film layers of Sb2Te3 and Bi2Te3.
Lead telluride and its alloys
SiGe
Materials based on nanotechnology
21. 21
A plot of various p-type semiconductor
figures of merit times temperature vs. temperature are
shown. Within the temperature ranges concerned in
electronics cooling (0-200C) Bi2Te3 performs the best.
Similar results are shown for n-type semiconductors
22. 22
Bi2Te3 Properties:
Below is a plot of the figure of merit (Z), Seebeck
coefficient, electrical resistivity, and thermal
conductivity, as a function of temperature for Bi2Te3.
Carrier concentration will alter the values below.
Bi2Te3 figure of merit as a function of tellurium
concentration.
23. 23
Condensation
A common problem with TE cooling is that
condensation may occur causing corrosion and eroding
the TE’s inherent reliability.
Condensation occurs when the dew point is reached.
The dew point is the temperature to which air must be
cooled at constant pressure for the water vapor to start
to condense Condensation occurs because the air loses
the ability to carry the water vapor that condenses. As
the air’s temperature decreases its water vapor carrying
capacity decreases.
Since TE coolers can cool to low and even below
ambient temperatures, condensation is a problem. The
most common sealant employed is silicon rubber.
Research has been performed to determine the most
effective sealing agent used to protect the chip from
water. Four sealants were used to seal a TE cooling
device and the weight gain due to water entering the
device measured. The best sealants should have the
lowest weight gain. The epoxy has virtually no weight
Gain
24. 24
According to the previous results, it seems that the epoxy
is the best sealant. These results are verified by the
published permeability data showing the epoxy having the
lowest permeability (vapor transmission rate) of all the
sealants.
25. 25
Thermoelectric Performance
TE performance depends on the following factors:
The temperature of the cold and hot sides.
Thermal and electrical conductivities of the
device’s materials.
Contact resistance between the TE device and
heat source/heat sink.
Thermal resistance of the heat sink.
Coefficient of Performance
A typical AC unit has a COP of approximately 3. TE
coolers usually have COP’s below 1; 0.4 to 0.7 is a
typical range.
Below are COP values plotted versus the ratio of
input current to the module’s Imax specification. Each
line corresponds with a constant DT/DTmax (the ratio
of the required temperature difference to the module's
max temperature difference specification).
27. 27
CHAPTER: 3 MATERIALS USED
EVAPORATOR:-
• A mini sized Evaporator is made of Aluminum
as it retains cooling effect for long period.
• The size of Evaporator is 15*12*23 = 4140 cc
Aluminium box recieves chilling effect from one side of the
peltier and transfer to the the storage.
28. 28
Pump:-
A pump is a device that moves fluids. Pumps are selected for
processes not only to raise and transfer fluids, but also to
meet some other criteria. This other criteria may be constant
flow rate or constant pressure.
In this project pumping system is provide to water
inorder to circulate around the hotside of the peltier. It is
done because the rate of heat dissipation is higher with
water rather than fan. This increases the efficiency of the
system.
The water pump employed is mini sized, it is capable of
running at 12v and 5Amp
29. 29
SUMP:
A sump is a cubiodal shape water container in which
pump is employed for circulation of coolant.the size of the
sump employed in this project is 20*130*200 mm.
Sump serves as a base part of peltier cooler, on which
evaporator is mounted. The peltier that is attached to the
bottom side of the evaportor is fixed with heatsink over it
which is submerged in the water of the sump.
30. 30
12V –BATTERY:-
Peltier device is powered by 12v battery.
an electric battery is a device consisting of two or
more electrochemical cells that convert stored chemical
energy into electrical energy. each cell has a positive
terminal, or cathode, and a negative terminal, or anode. the
terminal marked positive is at a higher electrical potential
energy than is the terminal marked negative. the terminal
marked negative is the source of electrons that when
connected to an external circuit will flow and deliver energy
to an external device.
`
`
31. 31
HEATSINK:-
HEATSINK is a passive heat exchanger that transfers the
heat generated by an electronic or a mechanical device into a
coolant fluid in motion. Then-transferred heat leaves the
device with the fluid in motion, therefore allowing the
regulation of the device temperature at physically feasible
levels.. The heat sink used in this fridge is of the dimension
7.5cm X 8cm X 4.5 cm (L x B x H).
32. 32
Insulation Material:-
As we know the ice vendors take advantage of thermocol for
its economic value and good insulation property as it does not
allow the inner temperature of cooling medium to go down. Hence
it is also an economic source of insulation. So the external
structure of the whole refrigerator is made of thermocol.
PLASCTIC TUBE:-
Plastic tube conveys the water from the sump to the peltier
device which is employed at the upper side of the evaporator
box. One end of the tube is connecting to the water pump
and another is connected to a section attached to the peltier.
33. 33
Chapter4:- Construction and Design
Dimensions of the Fridge
1. Outer dimensions
Length 160mm
Breadth 110mm
Height 240mm
2. Inner dimensions
Length 150mm
Breadth 100mm
Height 230mm
3. Volume of the Fridge 3450000mm3
4. DIMENSIONS OF PELTIER 40mm x 40mmx 2mm
34. 34
STEPS IN THE CONSTRUCTION OF THE FRIDGE
Firstly a box of Thermocol is made of given dimensions and
then the aluminum box is made and fixed into it.
The aluminum box is mounted with a Peltier device at
the top and bottom with the help of thermal paste.
At the top of the aluminum box a small rectangular box
is made in which hot side of the Peltier is faced.
Base of the evaporator is attached with cold side of the
Peltier and hot side is attached to a heat sink which is
submerged in sump water.
The sump is placed beneath evaporator has a pump and
heat sink submerged in it.
One end of the tube is connected to the Water Pump
and another end is connected to the small rectangular
box mounted on the top side of the evaporator.
A small rectangular has a channel to the sump in which
the water flows to the sump.
A battery is placed beside the evaporator with proper
insulation.
The terminals of the Peltier devices, and Pump should
be connected properly.
35. 35
Circuit diagram of fridge
Circuit diagram showing the Peltier and Pump connections
with a Power Source.
The circuit of the fridge is made quite simple and convenient
so that in case of any fault, it can be easily dissembled and
can be repaired without any major changes to the design.
The two Peltier units are used in series with each other
connected to the 12 volt DC supply. A pump is also
connected in series as same that of Peltier.
36. 36
Chapter 5 WORKING OF THE PROJECT
Fridge:-
The fridge is provided power supply form a 12 volt DC
7.5 amps battery.
To start the fridge, the switch on the fridge is turned on.
When the switch is turned on the Peltier devices and
Pump start functioning.
The water from the sump is pumped to the upper
smaller rectangle and directs to the hotter side of the
Peltier (P1).
The hot side of the second Peltier is cooled by the
sump.
Cold sides of the both Peltier transfers the chilling effect
to the evaporator.
The Peltier thermoelectric Device will be so arranged in
a box with proper insulation system and heat sink so
that efficient cooling takes place at all the time.
To turn off the fried, switch can be turned off.
37. 37
Calculation of COP of FRIDGE
1. Input power = product of current and voltage = ------
----- W
2. Initial temperature of the evaporator = --------K
3. Final temperature of the evaporator = --------- k
4. Total amount of heat removed = Total cooling effect
produced
5. Total amount of heat removed = Mw* cp * change in
temperature = --------------------- = -------------
6. Coefficient of performance = refrigeration effect / input
work= -------------------
38. 38
Chapter6: COST ANALYSIS
The cost analysis for this project is done as follows. All the
components along with the miscellaneous cost are
included in the total cost of this fridge.
S.No Name of the Material / Equipment Cost Rs.
1. Peltier devices -2 660/-
2 Aluminum box 200/-
3 Thermocol box 200/-
4 Pump 300/-
5 Battery 12v 650/-
6 Heat sink – 2 400/-
7 Thermal paste 80/-
8 Plastic tube 50/-
9 Sump 60/-
10 Insulating material 150/-
Total cost Rs.2750/-
The cost Analysis shows that the Overall Cost of the Project
strikes Rs. 2750/-
39. 39
CHAPTER 7 CONCLUSION
During construction of the device several minor changes
were made to the design. Each of these changes we feel was
justified as they made for easier construction while
maintaining the performance of the device with respect to
the project goals. The device passed its final inspection and
was deemed to have a professional appearance by the design
project coordinator
The device was discovered to have ample precision and
total heat transfer capabilities while meeting its accuracy
requirement.
REFERENCES
1. Wikipedia https://en.wikipedia.org/wiki/Main_Page
2. Google.com
3. Astrain D and Vian J G (2005), “Computational Model for Refrigerators Based on
Peltier Effect Application”, Applied Thermal Engineering,
4. Christian J L and Jadar R Barbosa Jr (2011), “Thermodynamic Comparison of
Peltier, Stirling, and Vapor Compression Portable Coolers”, Applied Energy, Vol.
5. Roy J Dossat (2002), Principles of Refrigeration, Vol. 2
