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Please forgive me ahead of time if something I say isn't correct, I've just started to read about thermodynamics ever since I developed a fascination for the anti-griddle (by the way does anyone know how one of those works?) Anyways, I've been reading up on different methods of cooling, and I am very intrigued by adiabatic cooling (demonstrated most commonly by a can of compressed air).

I think I understand why the highly pressurized air, when released, becomes cold:

  • the expansion of the pressurized gas from a small to a larger volume causes the energy to decrease and the gas to become cold
  • the resulting loss of energy within the can causes the temperature to decrease dramatically

Please correct me if the above is wrong, but I am wondering where heat is being generated in this system? It seems like the air is being cooled and so is the can, but is nothing being heated to counteract the cooling? Also would we see the same results in a closed system?

Imagine a can of compressed air inside a vacuum chamber, as the gas is released, would the can and air around it be cooled? I have a feeling that the work done in such a system would be zero, and as such there would be no temperature changes, but I am unsure. However if the can were to be cooled, would there be a way of recompressing air into the can and repeating the process to create a cooling system?

I appreciate any thoughts or corrections on my understanding of this topic.

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Your intuition is correct; if you use an ideal gas, the temperature will be unchanged. However, in a real gas there are extra attractive forces between the molecules, so that it costs energy for the gas to expand. The keyword to search for is the 'Joule-Thomson effect'.

This cannot be used as a free refrigerator (which would violate the 2nd law) because the gas will heat back up when you compress it again.

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