A three-dimensional numerical model of Ranque-Hilsch vortex tube has been developed using the commercial CFD code (Star-CD) to analyze the flow parameters and energy separation mechanism inside the tube. Investigations have been done on the variation of fluid properties and flow parameters as the fluid particles progress in the flow field by tracking different particles exiting through the hot and cold end. Fluid properties like stagnation temperature, static temperature, static pressure and total pressure and flow parameters like axial, radial and swirl velocities are obtained along the axial and radial directions to understand the flow behaviour inside the tube. The presence of free vortex zone inside the tube also has been investigated. Possible energy transfer mechanisms are discussed and an estimate has been made on the magnitude of energy transfer from the cold end exit flow to hot end exit flow. Effects of secondary circulation and length of the tube on energy separation also have been evaluated. (C) 2008 Elsevier Ltd. All rights reserved