I see what you are saying... You are saying that if you send it down a tube as compressed air, or air under great pressure, but not so much that it transforms to liquid, and then sorta expands into a different pressure zone hopefully drawing some heat into the equation? Ok here are a few problems...
1. You are still going to need a compressor. However, the gas under different pressures is just going to create faster moving air in certain areas. Imagina a can of air, like the computer dusting stuff. It's compressed, into a liquid as a matter of fact. As you press the trigger, the air decompresses and flys out at a rapid speed. But the only reason why this happens is because the pressure is so much less on the outside. If you are going to have a closed system, you might be able to get 2 sides with different air pressures, but they will not be able to mix. And if they do they will stabilize. Imagine you have 2 different compressed areas C1 and C2. And then you have the compressor- C. You might be able to get a setup like this- C1-C-C2-C and repeat. Now since the all the air pressure in the C1 compartment is the same, no air will be moving faster there. And Since the air pressure in the C2 compartment is the same, no faster air there either. A great amount of energy is required to change the state of matter. When that transformation takes place is when you get the desired affects.
Geez.. I can't remember my other points now lol. I'll write later if I remember them.