The Ranque-Hilsch vortex tube is a simple device which splits a compressed gas stream into a cold stream and a hot stream. The process of energy separation taking place in the vortex tube has been investigated theoretically and experimentally. The analysis of the dimensional groups that govern the tube performance as a cooling device have shown that; for geometrically similar tubes, the inside diameter of the tube is a parameter. This conclusion was verified experimentally. The experimental results have also indicated that there is an optimum tube diameter for best cooling
performance. It was also shown that the ratio between the temperature drop of the cold stream achieved at a certain pressure ratio to its maximum value (To - Tc)/(TO - Tc)max can be expressed by a sole function of the cold mass fraction U (U: kg. cold air per kg. supply air to the tube), and does not depened on other conditions of operation. On the other hand, the correlation between the analytical and experimental results have shown that the overall performance of the vortex tube can be expressed by a generalized formula which is valid for all conditions of operation. Stith formula can predict the cooling performance of the vortex tube from knowledge of its inside diameter, type of the working medium (expressed by the specific heat ratio Cp/Cv), its inlet condition (temperature 'To and pressure Po), the required cold stream pressure (Pc) and cold mass fraction (U).