Thermodynamic performance of a CO2 vortex tube based on 3D CFD flow analysis

Abstract

The vortex tube (VT) is a mechanical device that can simultaneously provide heating and cooling. In this work, a 3D CFD model is first developed to simulate the flow of CO2 within a vortex tube, and then it is validated with published experimental data. The assumed k-ε turbulence model uses Structured Hexahedral nodes generated in ANSYS Meshing. Only 1/6 of the geometry is required due to the symmetry of the VT. The validated CFD model is combined with a thermodynamic model of the VT to complete a parametric study, where the inlet pressure (550 kPa to 1300 kPa) and cold mass fraction (0.2–0.9) are the chosen parameters. The effects on the VT energy separation and performance are presented. Energy separation is discussed in terms of the hot exit and cold exit temperature differences, both with respect to the VT inlet temperature. Performance is characterized by cooling power, heating power, and both energy and exergy metrics. The numerical results show that the variation of the cold mass fraction from 0.2 to 0.9, for a fixed inlet pressure of 1300 kPa, causes the hot exit temperature difference to rise from 10 °C to 78.9 °C, while the cold exit temperature difference falls from 44.2 °C to 9.7 °C.