An experimental investigation of the optimum geometry for the cold end orifice of a vortex tube

A vortex tube is a simple mechanical device, which splits a compressed gas stream into a cold and hot stream without any chemical reactions or external energy supply. This paper presents the results of a series of experiments focusing on various geometries of the "cold end side" for different inlet pressures and cold fractions. Specifically, the tests were conducted using different cold end orifice diameters. Energy separation and energy flux separation efficiencies are defined and used to recover characteristic properties of the vortex tube. These are used to show an appropriate scale to non-dimensionalize the energy separation effect. The experimental results indicate that there is an optimum diameter of cold end orifice for achieving maximum energy separation. The results also show that the maximum value of energy separation was always reachable at a 60% cold fraction irrespective of the orifice diameter and the inlet pressure. The results are compared with the previous studies on internal flow structure, and optimal operating parameters are shown to be consistent with a matching of orifice size with the secondary circulation being observed.