Abstract: A method for the design of a vortex tube for energy separation, the vortex tube having a long tube with a diameter Do, a diaphragm closing one end of the tube having a hole with diameter d.sub.1 in the center, one or more tangential nozzles with a total area F piercing the tube just inside the diaphragm, and a throttling valve at the far end of the tube, wherein conventionally describing in terms of the relative parameters are as follows:P=pressure ratio=gas pressure ahead of the vortex tube nozzles divided to gas pressure downstream the diaphragm.mu.=cold fraction=mass flow of cold gas divided by mass flow of the inlet gass=relative area of the nozzles ##EQU1## d=relative diameter of diaphragm: d.sub.1 /Do and wherein P is between 5.0 or less and more than 1.0 and d is between approximately 0.4 and approximately 0.55 and .mu. is between 0.4 and approximately 0.65, then s is selected to be between 0.08 and approximately 0.12; and wherein P is between 5.0 and approximately 10.