Computational study of energy separation in convergent-divergent vortex tube for different throat diameters, throat locations, inlet pressures, and working gas

This paper aims to improve the energy separation performance of vortex tube with a converging-diverging design of the hot tube. Three-dimensional computational fluid dynamic simulations are conducted to explore energy separation in a straight vortex tube (SVT) and in convergent-divergent vortex tubes (CDVT) with variations in throat diameter, throat position, inlet pressure, and working gas. Detail analysis of flow and temperature distributions reveal that flow is accelerated in the converging part of CDVT, which increases the transfer of shear work from the axial region to the peripheral region of CDVT compared to SVT, thereby producing significantly higher cold temperature separation in CDVT compared to SVT. CDVT with non-dimensional throat diameter of 0.40 is observed to produce the maximum value of cold temperature separation, which is up to 9 K (similar to 35 %) higher than the same obtained with SVT. Coefficient of performance of cooling obtained with this CDVT is found to be up to similar to 30 % higher compared to SVT. When CDVT is operated with helium, Delta Tc is found to have mean increment of 20 K (56 %) compared to SVT being operated with air. Overall, CDVT having nondimensional throat diameter of 0.40, throat position in the middle of the hot tube, and operating with helium is recommended for obtaining maximum temperature separation performance in a wide range of cold mass fraction.