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Submitted by

MUDAVATH BABURAM

13001-M-036

Under the Guidance of

Mr. ANAND

(Lecturer)

FOR THE PARTIAL FULFILLMENT OF THE DIPLOMA IN

MECHANICAL ENGINEERING

2013-2016

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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.

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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)

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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.

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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.

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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

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CHAPTER:3 MATERIALS USED 26

CHAPTER:4 CONSTRUCTION AND DESIGN

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CHAPTER:5 WORKING OF FRIDGE 35 CHAPTER:6 COST ANALYSIS 37

CHAPTER:7 CONCLUSION 39

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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.

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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

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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.

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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

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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.

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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.

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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.

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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.

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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.

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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.

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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

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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

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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.

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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

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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

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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.

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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

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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.

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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).

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DESIGN METHODOLY OF TE

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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.

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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

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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.

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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.

`

`

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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).

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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.

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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

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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.

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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.

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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.

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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= -------------------

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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/-

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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