Numerical simulation of supersonic separator with axial or tangential outlet in reflow channel

Abstract

In the separation process of the conventional supersonic separator, the shock wave easily appears in diverging section of the nozzle and the swirling flow occurs in subsonic conditions with poor efficiency, which make the low temperature section short and the cooling effect dissatisfied. In this paper, a novel supersonic separator with reflow channel that has axial outlet or tangential outlet has been designed. The fluid can be drawn into the nozzle by the differential pressure between the discharge clearance on the wall and the throat zone near the centerline. Axial and radial distribution of the main parameters and the effect of pressure ratio are investigated with Reynolds Stress Mode (RSM) turbulence model. The results show that compared with the device without reflow channel, the pressure recovery in the diffuser with reflow channel is faster, the centrifugal acceleration is higher and the temperature is lower, which manifest the new device has a better refrigeration and separation performance. The supersonic separator with axial reflow outlet can obtain the better performance with pressure ratio of 1.5 that has a low temperature (221 K) and high centrifugal acceleration (2.2 × 107 m/s2), while the high centrifugal acceleration (9.89 × 109 m/s2) and low temperature (223 K) can be achieved in the device with tangential reflow outlet when pressure ratio is 2.0. Moreover, the structure with axial reflow outlet enlarges the supersonic region in the novel device and has a better ability to resist flow fluctuation and backmixing under the same condition when pressure ratio is 1.5. As the pressure ratio increases, the position of shock wave shifts downstream and the centrifugal acceleration and the reflow impetus increase, while the minimum temperature decreases, which prove that the increasing pressure ratio can improve the fluid expansion characteristics.