Numerical investigation of gas species and energy separation in the Ranque–Hilsch vortex tube using real gas model

A three dimensional Computational Fluid Dynamics (CFD) model is used to investigate the phenomena of energy and species separation in a vortex tube (VT) with compressed air at normal atmospheric temperature and cryogenic temperature as the working fluid. In this work the NIST real gas model is used for the first time to accurately compute the thermodynamic and transport properties of air inside the VT. CFD simulations are carried out using the perfect gas law as well. The computed performance curves (hot and cold outlet temperatures versus hot outlet mass fraction) at normal atmospheric temperature obtained with both the real gas model and the perfect gas law are compared with the experimental results. The separation of air into its main components, i.e. oxygen and nitrogen is observed, although the separation effect is very small. The magnitudes of both the energy separation and the species separation at cryogenic temperature were found to be smaller than those at normal atmospheric temperature.