Ranque-Hilsch Vortex Tube (Interactive Simulation) 

Cooling the exterior might help to some degree, as the cooling of the inner vortex is caused by the outer vortex "stealing" energy to stay at the outside. Or perhaps the inner vortex is pushing energy into the outer gas because it has a tighter radius. Either way, it's energy transfer towards the outer vertex. If we pull energy away from that outer vortex by keeping it cool, then we should see a drop in temperature at both ends, a larger feed fraction at the cold end, or perhaps a reduction in tube length, as the energy needed to keep the outer vortex spinning is increased.

@@timh.6872 I see that in theory, a larger diameter and longer tube will have more surface area to give up its extra heat, maybe increasing the COP. Furthermore, actively cooling the outside of the tube will cool the cold side gasses. But, active cooling the outside is another issue. Either way, we don't see really long huge tubes for some reason. Maybe there's more friction with the wall, or more time for friction between the inner and outer vortex. Or maybe other factors. I think the inlet gas stream is a gas of molecules with various velocities. I think that as it vortexes, the faster higher energy molecules tend to the outside while the slower ones tend to the inside.

@@kreynolds1123 I did far too much research on this last night. The consensus, currently, on how it works is that the two vorticies trade energy from inner to outer, essentially making a simultaneous compressor and expander. This only works if the vorticies are distinct, so making the tube even longer might break the clean biaxial flow we need for it to work. It's also general consensus that this only works at high pressure differences, 1.9:1 inlet to outlet or better, as there are supersonic effects at play in the swirl chamber. However, I did come across a paper that seemed to show significant cooling at much lower pressure ratios, so I'm not completely convinced that a low-pressure "temperature separator" vortex tube is impossible

@@timh.6872 I had almost forgotten this. Now I want to know 😉 Too bad, I have 100 other projects vying for my time and not enough money for each. 😎

*despite being fantasy-fearing men