4. Thermoelectric Materials
A material that can be used to convert
thermal energy into electric energy or provide
refrigeration directly from electric energy.
Eg :
Bismuth chalcogenides (Bi2Te3 & Bi2Se3 )
Lead telluride (PbTe)
4http://www.sigmaaldrich.com/materials-science/metal-and-ceramic-science/thermoelectrics.html
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5. History Of Thermoelectric effect
• Seebeck found that a circuit made from two
dissimilar metals, with junctions at different
temperatures would deflect a compass
magnet
• Peltier found that an electrical current would
produce heating or cooling at the junction of
two dissimilar metals.
5
6. Seebeck Effect
An electric current would flow continuously in a
closed circuit made up of two dissimilar metals, if
the junctions of the metals were maintained at
two different temperatures.
𝐒 =
∆𝑽
∆𝑻
Where;
𝐒 – Seebeck Coefficient
∆𝑽 – Voltage Difference
∆𝑻 – Temperature Gradient
6
7. Peltier Effect
An electrical current would produce a
temperature gradient at the junction of two
dissimilar metals.
7http://www.thermoelectrics.caltech.edu/thermoelectrics/history.html
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8. Materials selection criteria
1.Figure Of Merit
The potential of a material for thermoelectric
applications is determined in large part to a
measure of the material’s dimensionless figure of
merit,
ZT =
S 𝟐
𝝈𝑻
𝒌
ZT =
S 𝟐
𝑻
𝝆𝒌
𝒌 = 𝒌e + 𝒌g
8
9. where,
S - Seebeck Coefficient
ρ - Electrical Resistivity
k - Thermal Conductivity
ke - Electronic Conductivity
kg - Lattice Conductivity
Note:
Low electrical resistivity and thermal conductivity
are required for high figure of merit.
These values are temperature dependent
therefore, the figure of merit is temperature
dependent.
p and n type material have different figures of merit
and are averaged to determine a materials overall
quality.
9
10. 2. Power Factor
Under a given temperature difference, the ability of
a material to produce useful electrical power is
quantified by its power factor,
Power Factor = σS2
3. Device efficiency
The efficiency of a thermoelectric device for
electricity generation is given by ɳ.
ɳ =
𝑬𝒏𝒆𝒓𝒈𝒚 𝒑𝒓𝒐𝒗𝒊𝒅𝒆𝒅 𝒕𝒐 𝒕𝒉𝒆 𝒍𝒐𝒂𝒅
𝑯𝒆𝒂𝒕 𝒆𝒏𝒆𝒓𝒈𝒚 𝒂𝒃𝒔𝒐𝒓𝒃𝒆𝒅 𝒂𝒕 𝒉𝒐𝒕 𝒋𝒖𝒏𝒄𝒕𝒊𝒐𝒏
10http://www .sigmaaldrich.com/materials-science/metal-and-ceramic-science/thermoelectrics.html
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11. Thermoelectric power generation
A thermoelectric power generator is a solid state
device that provides direct energy conversion from
thermal energy into electrical energy.
Principle of operation is “Seebeck Effect”.
Thermoelectric generators contain no moving
parts and completely silent.
Thermoelectric generators have been used
reliably for over 30 years of maintenance-free
operation
11http://www.electrochem.org/dl/interface/fal/fal08/fal08_p54-56.pdf
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13. Uses Of Thermoelectric Generators
1. Harvesting automobiles produce waste heat
energy
2. Industrial processes waste heat reused to
generate electricity
13
14. 3. Used as power sources in satellites, space probes
(Radioisotope thermoelectric generator)
3. For small portable applications,
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15. Thermoelectric (TE) Cooling
Thermoelectric cooling uses the “Peltier effect” to
create a heat flux between the junction of two
different types of materials.
The amount of heat that can be absorbed is
proportional to the current and time.
15
W = PIt
http://www.tec-microsystems.com/EN/Intro_Thermoelectric_Coolers.htm
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17. 17
The most efficient
configuration of producing
TEC
One side is attached to a
heat source and the other a
heat sink that remove the
heat away.
The electrical insulator must
have a high thermal
conductivity
Ceramics like alumina are
generally used as a insulator
18. Which Industries Use TE Cooling?
1. Electronic
2. Medical
3. Aerospace
4. Telecommunications
18
19. Uses Of Thermoelectric Cooling
1. Laser diodes Cooling
2. Laboratory sample cooling
19
TE
Si bench
22. Advantages of TE
Environmentally friendly
No moving parts so maintenance is required less
frequently
No chlorofluorocarbons
Reliable source of energy
Recycles wasted heat energy
Has a long life, with mean time between failures
(MTBF) exceeding 100,000 hours
Scalability, meaning that the device can be applied
to any size heat source from a water heater to a
manufacturers equipment
22
23. Disadvantages Of TE
Slow technology Progression
Requires relatively constant heat source
Low energy conversion efficiency rate
Lack of customer/ industry education about
thermoelectric generators
Able to dissipate limited amount of heat flux.
Lower coefficient of performance than vapor-
compression systems.
Relegated to low heat flux applications.
23http://thermoelectricgeneratorgeneration.blogspot.com/2010/06/thermoelectric-generators-advantages.html
Access on 26.7.2014