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Hey guys, while learning thermodynamics i wondered how a the principle of a heat pump would look at a microscopic level, not on a quantum mechanical level.

I learned that when a hot and a less hot body are in direct contact, the heat is transferred by the kinetic energy of the atoms, so to speak the vibrating atoms of the hot body kick the ones of the cooler ones and so transfer heat.

In the case of a heat pump, to maintain a increase in total entropy one needs to add mechanical work to get a cool body transfer heat to a body with a higher temperature (I hope this is correct). But how do the atoms of the cooler body interact with those of the warmer? If they would collide (along with their smaller kinetic energy) with those of the warmer body (along with their greater kinetic energy) I would intuitively say that nothing would happen...

So how does that work? :)

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I'll bite. You have a small chamber where you keep a gas. To heat it up you apply mechanical force to it so as to decrease its volume. To cool it you let it do work on your mechanical force so that its volume increases. This pumps heat in and out so move the two heat baths appropriately.

Surely there are some more elegant methods that could be constructed physically. I would suggest spin interactions as a way of making a heat pump. Another place to look is in the electrically powered heat pumps now used to cool some integrated circuits. See:
"Thermoelectric Effect"
http://en.wikipedia.org/wiki/Thermoelectric_effect

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