Flow visualization of supersonic two-phase transcritical flow of CO2 in an ejector of a refrigeration system

Abstract

Supersonic two-phase flow of CO2 in an ejector was investigated in flow visualization experiments. The ejector was installed in a transcritical CO2 ejector-expansion refrigeration system with a convergent primary nozzle and a rectangular mixing chamber. The flow fields in the suction chamber and the mixing chamber of the ejector were visualized by direct photography for various operating conditions. The results showed that the liquid in the primary flow after the primary nozzle exit increased with increasing primary flow and secondary flow pressures. The expansion angle of the primary flow at the nozzle exit decreased with increasing secondary flow pressures. The primary flow was blocked in some cases at the mixing chamber entrance due to the large expansion angle which reduced the entrainment performance. The entrainment ratio was inversely related to the expansion angle. The primary and the secondary flows had a short mixing region in the mixing chamber with the mixed flow quickly becoming uniform.