I think I've found Maxwell's Demon, however the demon is quite large...

[Low-Q]

Well, fluids with faster density response to temperatur change are often less densed and less capable of transferring energy.

Many thoughts goes through my mind these days. I have been thinking, if the process in a heat exchanger have a COP of 4-5 (500% energy out compared to input energy), should make it possible to boost the energy harvesting from the air. Think of heat engine which is directly and thermally connected to this process, the engine could have little more than 20% efficiency and be suficcient to run the pump.

The expansion nozzle is pure loss, so what we need to increase the efficiency of the heat exchanger even more, is to place a reversal pump that is run by the pressure made by the main pump. This reversed pump must deliver less volume pr. revolution than the pressure pump in order to maintan the pressure difference between cold and hot sides. With such a reversed pump (expansion pump) if you like) will reduce the input power by 20%, and therfor increase COP to 6 or 7. Then we can talk about an engine that runs on pure air temperature

Vidar.

[broli]

I was thinking about the rotational setup and a simple design for it which could be utilized as proof of concept. I attached such setup below. Basically it's made of brass or copper pipes and a T pipe fitting. The lower parts are insulated while the upper part is open. A contactless IR thermometer could be used to measure the temperature on the upper part, which should be the hot part.

But to be honest for reasonable dimensions (sub 1 meter diameter) you would need some high valued parameters. The rotational speed has to be at least 10000 RPM to see accelerations that are near 10-20 g's.

Hopefully such a setup would be conclusive and show a significant temperature increase if the theory of the concept is sound and perhaps lead to more ideas, designs and concepts to improve it and multiply the difference by stacking.

Edit: I was quite a bit off with the acceleration numbers. 10000 RPM can lead to  10000-20000 g's at a radius of 10-20 cm!.