In the present study, three dimensional computational fluid dynamic simulations are carried out to understand the energy separation in the counter-flow vortex tube. The objective of the work is to understand the flow features that affect the energy separation between the core and peripheral flow layers inside the vortex tube. Trapezoidal shaped inlets of varying numbers from one to six are compared and analyzed, while the total inlet mass flow rate and other geometrical parameters are held constant with air as a working fluid. From the results, highest temperature separation is observed with single inlet as observed in the literature. Further, the vorticity and turbulent kinetic energy at the dividing line between core and periphery decrease with the increase in number of inlets. To understand the same, streamlines are visualized. Analysis reveals that higher core flow layer diameter, lower mean pitch distance and longer residence time are the main factors affecting energy separation. It is also found that secondary circulation vortices are prominent with the single inlet. The size of these vortices regardless of the number plays a key role in energy separation. © 2017 Elsevier Ltd