Three-dimensional numerical simulations of a Ranque-Hilsch vortex tube working with subcritical carbon dioxide

Numerical simulations of a Ranque-Hilsch vortex tube working with subcritical carbon dioxide (CO₂) are performed using different modeling approaches assessed in terms of accuracy and computational cost. Three different fluid properties models and two turbulence models in both high and low Reynolds number formulations are compared to experimental data available in the literature. The ability of the models to predict the cold mass fraction as well as the temperature separation is discussed. A deep insight into the internal flow characteristics is then carried out to assess the assumptions made by one-dimensional thermodynamic models. For the range of operating conditions, results show a fairly good agreement in terms of cold mass fraction, cold and hot outlet temperatures, and hot outlet pressure with high Reynolds approaches, while the k-ω SST model performs better to predict the internal flow characteristics in conjunction with the Span-Wagner equation of state. To the best of the author's knowledge, the similarity between the Bödewadt flow and the boundary layer flow along the wall facing the hot exit is confirmed for the first time in a Ranque-Hilsch vortex tube working with subcritical CO₂.