Abstract: The energy separation by a vortex tube, with ideal CO₂ gas medium, was mathematically formulated with a standard k-ε turbulence model and numerically simulated.The influence of the nozzle flow path number on the flow field profiles and energy separation was investigated under the conditions, including an inlet temperature of 298.15 K, an inlet pressure of 6.5 MPa and a cold flow rate of 0.1.The simulated results show that the nozzle flow path number significantly affects the refrigeration and heating of the vortex tube.For example, as the flow path number increases from 2 to 6, both the axial/radial temperature and pressure distributions change in a decrease-increase manner, resulting in an increase-decrease variation of refrigeration.An optimized nozzle flow path number of 3 accounts for the most effective refrigeration and heating of the vortex tube.