ejector expansion refrigeration system, transcritical CO2 ejector, phase change, pressure measurement
Complex flow processes exist in the primary convergent-divergent nozzle of a transcritical CO2 ejector because of the rapid expansion of the supercritical CO2 flow, which have a significant influence on the performance of a transcritical CO2 ejector expansion refrigeration system. A visualization experiment with the direct photography method was carried out to investigate the phase change phenomena in the primary convergent-divergent nozzle of a transcritical CO2 ejector. The visualization transcritical CO2 ejector was designed as a rectangular cross section to minimize the optical distortion. In order to better interpret the phase change phenomena of CO2 flow, four pressure measurement points were lumped in the convergent-divergent nozzle to get the pressure distribution along the convergent-divergent nozzle for various operating conditions. The results revealed that the phase change position in the convergent-divergent nozzle was closely related to the primary flow inlet conditions and the suction flow inlet pressure. .The results showed that the phase change could start after or before the nozzle throat, and the phase change position moved upstream by decreasing the primary flow inlet pressure and temperature simultaneously. As keeping the primary flow inlet pressure constant, the phase change position also moved upward by decreasing the suction flow inlet pressure. In addition, the measured pressure results indicated that the pressure differences in the convergent section of the primary convergent-divergent nozzle increased as the CO2 suction flow inlet pressure decreased because of more adequate expansion of the primary flow.