Computational Fluid Dynamics of Energy Separation in Vortex Tube

Abstract

Devil’s Tube is the name that some researchers chose for Ranque-Hilsch vortex tube because of the ambiguity of its working mechanism. In an attempt to unveil the principle of energy separations in this tube, this study uses the shear stress transport 𝑘−𝜔 turbulence model with viscous heating to investigate the flow structure inside the fluid domain and to examine the impact of the fluid’s properties on the performance of the temperature separation. Firstly, the flow parameters such as velocity, temperature, pressure, and density are plotted at various locations inside the tube. Thereafter, the energy separation performance is tested using five different gases, namely helium, air, oxygen, nitrogen, and carbon dioxide. In this regard, the effect of the gas properties, such as molecular weight, heat capacity, thermal conductivity, and dynamic viscosity are also examined. The study shows that the minimum cold temperature and the maximum hot temperature are achieved at different mass fractions and that the flow inside Ranque-Hilsch vortex tube consists of a forced vortex from r/R=0 to 0.9 and a free vortex from r/R=0.9 to 1. Furthermore, a comparison analysis is carried out to observe that helium yields the maximum separation while carbon dioxide yields the lowest; besides, one must account for viscous dissipation in modelling the energy separation in vortex tube. Moreover, energy separation performance improves with lower molecular weight and heat capacity, and higher dynamic viscosity of the working fluids, while no impact of the thermal conductivity is observed. Finally, it is concluded that the energy separation in vortex tube is due to the density gradient along the radial direction.