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Thermoelectric materials & Applications

A material that can be used to convert thermal energy into electric energy or provide refrigeration directly from electric energy

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Thermoelectric materials & Applications

  1. 1. Thermoelectric Materials & Applications 1 E.A.N.S.Edirisingha
  2. 2. Content  Thermoelectric Materials  History of Thermoelectric effect  Seebeck Effect & Peltier Effect  Materials selection criteria  Thermoelectric power generation  Thermoelectric (TE) Cooling  Advantages & Disadvantages 2
  3. 3. 3 Waste Heat to Electricity Thermoelectric
  4. 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 Access on 26.07.2014
  5. 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. 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. 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 Access on 26.7.2014
  8. 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. 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. 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 Access on 26.07.2014
  11. 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 Access on 26.7.2014
  12. 12. 12http://isen.northwestern.edu/news_media/articles/2014/04/21april2014_waste_heat_material.html Access on 4.8.2014 Thermoelectric Module Electric Insulators
  13. 13. Uses Of Thermoelectric Generators 1. Harvesting automobiles produce waste heat energy 2. Industrial processes waste heat reused to generate electricity 13
  14. 14. 3. Used as power sources in satellites, space probes (Radioisotope thermoelectric generator) 3. For small portable applications, 14
  15. 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 Access on 26.7.2014
  16. 16. Basic Principles  For n type TE materials  For p type TE materials 16
  17. 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. 18. Which Industries Use TE Cooling? 1. Electronic 2. Medical 3. Aerospace 4. Telecommunications 18
  19. 19. Uses Of Thermoelectric Cooling 1. Laser diodes Cooling 2. Laboratory sample cooling 19 TE Si bench
  20. 20. 3. Medical Sample cooling 4. Portable beverage coolers 20
  21. 21. 5. Climate-controlled jackets 21
  22. 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. 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
  24. 24. References  http://isen.northwestern.edu/news_media/articles/2 014/04/21april2014_waste_heat_material.html  http://www.electrochem.org/dl/interface/fal/fal08/fal0 8_p54-56.pdf  http://www.rsc.org/education/eic/issues/2012March/ thermoelectric-materials-nanoparticles.asp  http://www.tec-microsystems.com/ EN/Intro_Thermoelectric_Coolers.htm 24
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