The Hilsch Vortex tube…

Old Amateur Scientist article, might need to (re)make this to see if it really works – “With nothing more than a few pieces of plumbing and a source of compressed air, you can build a remarkably simple device for attaining moderately low temperatures. It separates high-energy molecules from those of low energy. George O. Smith, an engineer of Rumson, N. I., discusses its theory and construction” – Link.