Academic Article

This paper presents a numerical solution on a Ranque-Hilsch vortex tube using the ANSYS CFX-Solver to study the effect of geometric features on the energy separation inside the vortex tube. Comparing the numerical results with the experimental observes, this work showed that CFD analysis can predict the temperature separation effect that is consistent for the specific geometric. By changing geometric features and determining the temperature separation in every single shapes, this study tried to come down in favor of most effective scales for this device.

Introduction
This device was first discovered by a French physicist Ranque [1], but it was thermodynamically highly inefficient so it was abandoned for several years. After that Hilsch [2], a German engineer reported an account of his own comprehensive experimental and theoretical studies aimed at improving the efficiency of the device. So this device known with this two names. In recent years, various theoretical and analytical studies have been done on the vortex tubes.

A comprehensive study, about these researches has been done recently by Eiamsa-ard et al [3]. CFD has been used for investigating this phenomenon: Frohlingsdorf et al [4] studied flow and temperature field in a vortex tube, using CFX code and k- ε turbulence model. T.dutta [5] et al too used a computational fluid dynamics model to compare the influence of different Reynolds Averaged Navier-Stokes (RANS) based turbulence models in predicting the temperature separation in a Ranque-Hilsch vortex tube. U.Behera [6] et al evaluated the effects of number and type of inlet nozzles on the temperature separation, using STAR CD code and RNG k- ε turbulence model. Sachin.U et al [7] examined the role of the cold orifice to determine the conditions for maximum temperature and energy flux separation over a range of parameters.

In the first part of this study a three dimensional CFD model is used in order to simulated the flow phenomena. The second part discusses the influence of the geometric features on the performance of this device.

1. CFD modeling of vortex tube
The vortex tube is a mechanical device that can divide the compressed air into a hot and cold air. Due to having no mobile parts in the vortex tube, maintenance is not essential. Easier structure rather than other types of refrigeration systems is next advantage for this device.

When a high pressure air enters the vortex tube through the inlet nozzles, its expansion makes a quickly spinning vortex. The spinning gas goes through the pipe, some portion of its leave the tube at hot outlet that located in the end of the tube, and the other forced back along the central axis after reaching the cone which placed in the end of tube. The devices schematic is shown in Fig1.