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Comment by babyshake | Hacker News Reader

> The general idea is "lower air pressure and move gas to cold side so the gas heats up" followed by "raise air pressure and move gas to warm side so the gas cools down".

This sounds like Maxwell's Demon, where the work required to prevent the system from reaching thermodynamic equilibrium is equal to or greater than the extra energy. How does this differ from that?

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Maxwell says that the effort you put in is more than the work you can get out. So the heat difference you get, even if converted perfectly to other kinetic energy, will always be less than the electricity input.

But we aren't after kinetic energy, or work. We are after heat.

I thought heat was a form of kinetic energy? Specifically, it is a measure of the kinetic energy of an object's particles, independent of the kinetic energy of the object as a whole. That not accurate?

It technically is, but not really. The correct term is 'work' which means something like useful change in kinetic energy.

Your idea of 'kinetic energy of the object as a whole' is probably quite close.

Makes sense. I was thinking of it in context here. Seems the distinction between kinetic and thermal inside a heat pump is less useful that other places.

This is how a refrigerator works. No it does not violate the "Maxwell's Demon" thought experiment. Yes it does consume electricity, it's not for free. Efficiency gains are still good though.

This isn't decreasing entropy without doing any work like in the thought experiment.

Can you explain in more detail how it sounds like Maxwell's Demon? There's nothing that sounds like it sorts the air particles, so I don't see the connection.

Energy input in the form of compressor work. It's not even remotely similar to Maxwell's Demon.

Not at all. You use a compressor or some other means to increase the pressure. That's what the electricity is for.

Counterarguments to Maxwell's Demon is not that such chambers with a microscopic door cannot be fabricated, but that the Demon and his door cannot run without some entropy/power source outside to the chamber thereby negating the "negative energy" created by it. The Demon works if you don't mind feeding him and maybe adding fuel to the chamber as well, but then you're not getting the supposed free energy.

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