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Journal Bender_'s Journal: Comment about electrocaloric refridgerators

There has been quite some hype about 'compressor-free refridgerators'. Just some notes saved from comments I posted in the article. Probably gibberish to you if you are not a material science geek.

There are many ways to induce first order phase transitions in various system, leading to the release or take up of heat.

The special thing about the device in the article is that this phase transition is induced by an electric field, the so called electrocaloric effect. Therefore no movable parts in the system are required. Previously only small temperature differences have been demonstrated in metal oxides (small than 10K). By using ferroelectric/antiferroelectric polymers they are apparently able to increase the temperature difference to above 10K, which is a very significant increase.

That said, this of course typical university hype science and practial application faces many engineering and also intrinsic scientific problems. First of all they have not measured the temperature difference, but deduced it indirectly from maxwell relations. In a realistic set up the temperature difference will be lower.

A second problem is intrinsic to the material and has been conveniently neglected: Since the principle relies on a solid insulator the heat conductivitiy is extremely low. (No convection, no electronic heat conduction). This means that you are able to create a temperature gradient, but are not able to transfer a lot of heat, thereby severely limiting the cooling ability.

A third problem is that this effect only works in a very limited temperature range (above 70C). A fourth problem is hysteretic heating due to ferroelectricity...

Link to the original article: click

older work by the group

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