Your basic refrigerator and air conditioner work the same way. There is a compressor that compresses the "working fluid", typically freon. Compressing it makes it hot. The hot, high pressure fluid is allowed to flow through an external radiator where it gives up it's excess heat to the surrounding air. At the exit from the radiator there is the expansion valve that controls the amount of gas allowed through to the internal radiator. The pressure in the internal radiator is much lower than in the external one, so as the working fluid passes the expansion valve, it expands, and when it expands it gets much cooler. It gets so cold that it is colder than the inside of the refrigerator, so heat from the inside of the refrigerator is absorbed by the working fluid in the internal radiator. (I guess it's not proper to call it a radiator, since it is not radiating anything, but it functions just like a radiator: it maximizes the amount of surface area between the working fluid and the environment and so facilitates the transfer of heat energy from between the two.) After the freon has worked it's way through the internal radiator, it enters the compressor, and the cycle starts over.
I always thought this was a little weird. Here you have this high pressure gas, which you have gone to a lot of trouble to compress, and you are just venting it. Why aren't we using it to run some kind of engine? An engine performs the same function as an expansion valve, plus you could get energy back from it.
I imagine there are probably two reasons it hasn't been done:
- The present designs work. Companies build refrigerators and people buy them and feed them electricity. They do their job and people are willing to pay the cost of using them. Why spend a bunch of money on experimental research and engineering to build a product no one is asking for?
- It may not be possible to produce a compressed gas motor that would be efficient enough to produce a tangible benefit.
There are a couple of items that bear on this.
Vane-Type Motor |
There have been some attempts to build power generating stations that use the difference in temperature of water on the surface of the ocean and water from a hundred or so feet down. I haven't heard anything about them lately. Here they are generating power from relatively small differences in temperature.
The last little bit is something I tripped over recently, and that is the thermodynamic cycle used by refrigeration engineers makes no use of the potential energy in the compressed gas. That seems like an awfully big hole in such an established theory.
P.S. Here's an interesting A/C idea.
Update February 2017 replaced missing picture.
Did you know that Einstein invented and patented a refrigerator? The Einstein refrigerator is an absorption refrigerator which has no moving parts and requires only a heat source to operate. It was jointly invented in 1926 by Albert Einstein and his former student Leó Szilárd and patented in the US on November 11, 1930 (U.S. Patent 1,781,541)
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