Thermoelectric coolers and pellet size
the_anomaly, Sat Jul 26 2014, 02:17AMThermoelectric coolers or Peltier devices use P and N doped materials to turn heat into electricity or vice-versa. I've noticed the P and N materials are formed into pellets which are often only a few mm cubed in size. The two main disadvantages to these devices are their poor efficiency and relatively low heat pumping capacity when compared with current refrigeration techniques. This got me to wonder, why are the pellets so large? Why not etch them into a wafer microscopically? As I understand it (and I could be wrong) the more P-N junctions, the greater the amount of heat can be moved. Any thoughts?
Re: Thermoelectric coolers and pellet size
johnf, Sat Jul 26 2014, 04:40AM
Yes but as you decrease the size the resistance goes up swamping the peltier effect with Joule heating so efficiency plummets
johnf, Sat Jul 26 2014, 04:40AM
Yes but as you decrease the size the resistance goes up swamping the peltier effect with Joule heating so efficiency plummets
Re: Thermoelectric coolers and pellet size
Dr. Slack, Sat Jul 26 2014, 08:37AM
Just mucking about with the dimensions won't change the efficiency of the underlying material, though it may well suit any given arrangement to your particular specifications better.
Peiltier material has a difficult time, it needs high electrical conductivity so as to not generate too much parasitic heat when operating, and low thermal conductivity so it doesn't shunt all the heat back through the device. Now you will recognise that changing the dimensions changes both of these by the same amount in the same direction, so no joy there.
Current research into improving the electrical to thermal conductivity ratio has two main approaches a) Looking for different material combinations in the hope that para-excoticum-di-unobtanium-trioxide will work, and b) enhancing the materials already have, nanostructures, meta materials, doping and the like, to inhibit transport of the heat carrying phonons while avoiding making life difficult for the electrons and holes. Obviously there's some considerable crossover between those two, depending on your definition of material.
Dr. Slack, Sat Jul 26 2014, 08:37AM
Just mucking about with the dimensions won't change the efficiency of the underlying material, though it may well suit any given arrangement to your particular specifications better.
Peiltier material has a difficult time, it needs high electrical conductivity so as to not generate too much parasitic heat when operating, and low thermal conductivity so it doesn't shunt all the heat back through the device. Now you will recognise that changing the dimensions changes both of these by the same amount in the same direction, so no joy there.
Current research into improving the electrical to thermal conductivity ratio has two main approaches a) Looking for different material combinations in the hope that para-excoticum-di-unobtanium-trioxide will work, and b) enhancing the materials already have, nanostructures, meta materials, doping and the like, to inhibit transport of the heat carrying phonons while avoiding making life difficult for the electrons and holes. Obviously there's some considerable crossover between those two, depending on your definition of material.
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