The thermal separation flow characteristic in a vortex tube using a three-equation turbulence model is discussed in the present research. Flow behavior and energy separation of a vortex tube in different boundary conditions are investigated through a 3D model. The effect of the operating parameters on the turbulent viscosity ratio and the Mach number is also discussed. It was found that strong swirling flows with a high order of tangential velocity in the peripheral flow contributes to the rise in temperature due to viscous heating. Energy separation and cold-end side temperature depend mainly on the ratio of cold and hot-end side mass flow rates and the inlet conditions. Moreover, the effect of back pressure at cold-end side was investigated to determine how it alters the performance of the vortex tube. Finally, the results of the proposed computational fluid dynamics model are validated by the available experimental data.