This article describes the energy separation with the simulation of a three dimensional flow field in Ranque-Hilsch vortex tube. Rectangular and trapezoidal shaped inlets with varying aspect ratio are compared and analyzed while other geometrical parameters are held constant. Air is used as a working fluid. The nature of flow field inside the vortex tube is observed for different cases at an inlet pressure condition of 6 bar (absolute). From the results, it is observed that inlet with higher aspect ratio gives higher temperature separation. The trapezoidal inlet configuration is found to give higher temperature separation as compared to a rectangular shape. The streamlines emanating at the hot and cold end exits for both the rectangular and trapezoidal are visualized. Residence time for two shapes is calculated and found to be higher for trapezoidal shape. The increase in turbulence kinetic energy for the cold end exiting streamlines at the dividing region between core and periphery could be an important factor towards energy separation. (C) 2016 Elsevier Ltd. All rights reserved.