1. THERMOELECTRIC COOLING

2. CONTENTS INTRODUCTION BASIC PRICIPLES OF THERMOELECTRIC MODULES
BASIC MECHANISM OF THERMOELECTRIC COOLING
THERMOELECTRIC COOLING MODULES
HEAT SINK CONSIDERATIONS
PERFORMANCE GRAPH OF THERMOELECTRIC MODULE
APPLICATIONS OF THERMOELECTRIC COOLERS
ADVANTAGES OF THERMOELECTRIC COOLING
THERMOELECTRIC COOLING VERSUS TRADITIONAL REFRIGERATION

3. 1. INTRODUCTION
A thermoelectric (TE) cooler, sometimes called a thermoelectric module or Peltier cooler, is a semiconductor-based electronic component that functions as a small heat pump. By applying a low voltage DC power source to a TE module, heat will be moved through the module from one side to the other. One module face, therefore, will be cooled while the opposite face simultaneously is heated.

4. 2. BASIC PRICIPLES OF THERMOELECTRIC MODULES
THERMOELECTRICITY IS BSED UPON THREE
BSIC PRINCIPLES
SEEBECK EFFECT
PELTIER EFFECT
THOMSON EFFECT

5. SEEBECK EFFECT VO = AXY * (TH - TC)
Where: VO :- is the output voltage in volts. AXY :- is the differential Seebeck coefficient between the two materials, x and y, in volts/K . TH and TC, are the hot and cold thermocouple temperatures, respectively

6. PELTIER EFFECT QC or QH =PXY * I Where:
PXY is the differential Peltier coefficient between the two materials, x and y, in volts .I is the electric current flow in amperes. QC, QH is the rate of cooling and heating, respectively, in watts.

7. THOMSON EFFECT
When an electric current is passed through a conductor having a temperature gradient over its length, heat will be either absorbed by or expelled from the conductor. Whether heat is absorbed or expelled depends upon the direction of both the electric current and temperature gradient. This phenomenon is known as the Thomson Effect

8. 3. BASIC MECHANISM OF THERMOELECTRIC

9. N-TYPE SINGLE SEMICONDUCTOR PELLET

10. P-TYPE SINGLE SEMICONDUCTOR PELLET

11. ELECTRICALLY AND THERMALLY PARALLEL MULTIPLE PELLETS

12. THERMALLY PARALLEL AND ELECTRICALLT IN SERIES MULTIPLE PELLETS

13. N AND P-TYPE PELLETS

14. N AND P-TYPE MULTIPLE PELLETS

16. THERMOELECTRIC MATERIALS
The most often used in today's TE coolers is an alloy of Bismuth Telluride (Bi2Te3).
In addition to Bismuth Telluride (Bi2Te3), there are other thermoelectric materials including Lead Telluride (Pb-Te), Silicon Germanium (Si-Ge) and Bismuth-Antimony (Bi-Sb) alloys that may be used in specific situations.
Thermoelectric Materials should posses:-
Large Seebeck Coefficients (to minimize Joule heating).
High Electrical Conductivity.
Low Thermal Conductivity (to retain heat at the junctions)

17. APPROXIMATE FIGURE-OF-MERIT(Z)FOR VARIOUS TE MATERIALS

18. 4. THERMOELECTRIC COOLING MODULES
thermoelectric modules ranging in size from approximately mm (0.1 to 2.0 inches) square and 2.5-5mm (0.1 to 0.2 inches) in height.

19. 5. Heat Sink Considerations
A perfect heat sink would be capable of absorbing an unlimited quantity of heat without exhibiting any increase in temperature.
A heat sink temperature rise of 5 to 15°C above ambient (or cooling fluid) is typical for many thermoelectric applications.
Heat sink performance:- Qs= (Ts-Ta)/Q
Where
Qs:- Thermal Resistance in Degrees centigrade per Watt Ts:- Heat Sink Temperature in Degrees Centigrade. Ta:- Ambient or Coolant Temperature in Degrees Centigrade Q :- Heat Input to Heat Sink in Watts.

20. TYPES OF HEAT SINKS NATURAL CONVECTION HEAT SINKS
FORCED CONVECTION HEAT SINKS
LIQUID-COOLED HEAT SINKS

21. Forced Convection Heat Sink System Showing Preferred Air Flow

22. 6. PERFORMANCE GRAPH OF TE MODULE

28. 7. APPLICATIONS OF THERMOELECTRIC COOLERS
Include equipment used by military, medical, industrial, consumer, scientific/laboratory, and telecommunications organizations.
Uses range from simple food and beverage coolers for an afternoon picnic to extremely sophisticated temperature control systems in missiles and space vehicles.

29. 8. ADVANTAGES OF THERMOELECTRIC COOLING
No Moving Parts
Small Size and Weight
Ability to Cool Below Ambient
Ability to Heat and Cool With the Same module
Precise Temperature Control
High Reliability
Electrically "Quiet" Operation
Operation in any Orientation
Spot Cooling
Ability to Generate Electrical Power
Environmentally Friendly

30. Limitations of Thermoelectric Cooling Devices
Low C.O.P. and efficiencies make them unsuitable in places where economy is concerned.
There is also a limitation of their use in larger units.

31. 9. THERMOELECTRIC COOLING VERSUS TRADITIONAL REFRIGERATION
Solid state design
No moving parts
Integrated chip design
No hazardous gases
Silent operation
Compact and lightweight
Low profile
Sizes to match your component footprint
No bulky compressor units
Precise temperature stability
Tolerances of better than +/- 0.1°C
Accurate and reproducible ramp and dwell times
Cooling/heating mode options
Fully reversible with switch in polarity
Localized Cooling
Spot cooling for components or medical applications
Perfect for temperature calibration in precision detection systems
Rapid response times
Instantaneous temperature change
Reduced power consumption
Dehumidification
Efficient condensation of atmospheric water vapor

32. CONCLUSION
In spite of the fact that it has some disadvantages like low coefficient of performance and high cost, thermoelectric refrigerators are greatly needed, particularly for developing countries where long life, low maintenance and clean environment are needed. There is a lot of scope for developing materials specifically suited for TE cooling purpose and these can greatly improve the C.O.P. of these devices. Development of new methods to improve efficiency catering to changes in the basic design of the thermoelectric set up like better heat transfer, miniaturization etc. can give very effective enhancement in the overall performance of thermoelectric refrigerators. Finally, there is a general need for more studies that combine several techniques, exploiting the best of each and using these practically.       

33. REFRENCES http://www.thermoelectrics.com/introduction.htm

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