Numerical investigation of transient temperature separation phenomenon in vortex tube

Ranque-Hilsch vortex tube is a simple mechanical device with no moving parts. A high pressure feed gas enters the vortex tube through the swirl nozzles causing the feed gas to split into two thermodynamically different streams. These two streams will be having not only different velocities but also distinguished temperatures that are lower and higher than the inlet feed gas temperature. This phenomenon and the associated energy separation of the feed gas through the vortex tube are strongly dependent on such parameters as geometry, position, and number of the swirl nozzles, diameter and length of the vortex tube, inlet feed gas pressure, control valves, and aperture duct size. Although the vortex tube is used for few decades across different industries, energy separation phenomenon is still neither fully explained nor agreed upon by the scientific community. This paper is an attempt at a better physical understanding of the embedded phenomenon using computational fluid dynamics via a commercial software (Fluent Software) to numerically simulate the transient flow behavior of the feed gas as well as the energy separation, resulting in distinguished gas streams in a two-dimensional and axisymmetric vortex tube. Appropriate boundary conditions are employed in the numerical simulation resembling experimental conditions from the open literature with the exception of the gas exit at the hot end which has been set to be in concert with the operation of the flow-control valve. The obtained numerical results are in good agreement with experimental data from the open literature. Further, the numerical simulation confirms the existence of free and forced vortices and indicates that the temperature of the circumferential elements towards the hot end gets hotter by receiving heat from the core flow due to the kinetic to thermal energy conversion in the presence of viscous shear stresses.