Abstract
Flow behaviour and thermal separation mechanism on vortex tubes have been studied numer-ically. Rapid expansion indicated by high-pressure gradient near the inlet and the exit ports contributes to energy separation on the parallel and the counter flow vortex tubes. It creates a cooling process at the core region and drives an internal and rotational energy transfer to the peripheral region, then increases the gas temperature at the periphery along with friction due to the presence of the confined wall. Static temperature is related to static pressure in such a way that low pressure leads to the low static temperature at the same region inside the vortex tube. On the other hand, the high total temperature is found in the region with the low dynamic velocity. For both vortex tubes, the flow fields are mainly governed by the tangential velocity at the periphery and by the axial velocity at the core region. The maximum Mach number values based on the maximum tangential velocities in the inlet area for the counter and the parallel flow vortex tubes are 0.689 and 0.726, respectively, so both are compressible and subsonic flows. For the same size of geometry and boundary conditions, the parallel flow vortex tube has higher COP than the counter flow vortex tube i.e. 0.26 and 0.25, respectively.
Highlights
A vortex tube is a thermal-mechanical device that splits an inlet compressed gas into two streams at the outlet with higher and lower temperatures than the inlet one
The tangential velocity profile along z direction is identic for counter flow and parallel flow vortex tubes
Based on the velocities and temperature data, the maximum Mach number values for the counter and parallel flow vortex tubes are 0.689 and 0.726, respectively. Both are compressible flow but still in the subsonic flow regime. This tangential velocity decreases as the fluid progress along the axial direction and the minimum magnitude is found near the hot gas exit (z = 0.09 m)
Summary
A vortex tube is a thermal-mechanical device that splits an inlet compressed gas into two streams at the outlet with higher and lower temperatures than the inlet one. Flohlingsdorf and Unger [8] performed numerical investigations of the compressible flow and the energy separation in Ranque–Hilsch vortex tube using CFX code with k-ε turbulent model. Pouriya et al [12] have investigated the thermal separation flow characteristic in a vortex tube using a three- equation turbulence model. They concluded that the energy separation, cold-end side temperature and rise in temperature in the peripheral region depend mainly on the ratio of cold and hot-end side mass flow rates, the inlet conditions and swirling flow with high order tangential velocity. We use the same dimensions and number of grids for the counter-flow vortex tube (Figure 1)
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