A CFD analysis on the effect of tube curvature, hot flow control valve profile, and inlet swirl on the thermal performance of curved vortex tubes

The influence of tube curvature, conical valve geometry, and initial swirl on the thermal performance of vortex tubes is numerically investigated. Multiple models of straight and curved vortex tubes are developed in Ansys-fluent®. The effect of each parameter on flow and temperature fields is analyzed using 3d simulations with standard κ - ε turbulence model. The cold stream mass fraction is varied by controlling hot exit pressure. Truncated cone hot control valves are found to perform better than non-truncated valves, but the optimum truncation length depends on the application for which the vortex tube is to be used. The tube curvature too has a positive effect in raising the temperature separation between the two streams specifically for curvature angles larger than 150° with cold mass fractions ranging between 0.3 and 0.7. The performance of curved tubes can be improved further by combining curvature effect with other design changes such as the use of truncated cone hot flow valve and an optimum number of inlet nozzles. Three inlet nozzles have been found to produce an initial swirl that gives maximum cold stream temperature difference and maximum end-to-end temperature separation for the 110 curved vortex tube. The combined effect of the three parameters is studied for the 180° curved vortex tube with three nozzles and a truncated hot conical control valve. It is found that using this combination the cold stream temperature difference increased by about 23.4 percent while the end-to-end temperature separation improved by about 37.3 percent when compared with the straight vortex tube.