The ejector is one of the key components of a transcritical CO2 ejector expansion refrigeration system

and the nozzle exit position (NXP) is the main geometric parameter. Therefore

research on the structure

performance

and internal flow mechanism of the ejector is beneficial for improving the performance of the ejector system. In this study

a visualization ejector with different NXPs was designed and manufactured. The entrainment ratio and pressure recovery ratio of the CO2 two-phase ejector with different NXPs were obtained in a transcritical CO2 ejector expansion refrigeration system. Furthermore

the pressure distribution along the primary nozzle

mixing section

and diffuser section was measured using a pressure sensor. Simultaneously

the expansion angle

expansion length

and phase change position of the primary flow were captured using a high-speed camera. According to the experimental results

the performance of the ejector is influenced by the expansion profile. Specifically

the short NXP (4 mm) led to a short expansion length

large expansion angle

and high-pressure recovery ratio

but the corresponding entrainment ratio was relatively low. As the NXP increased to 6 mm and 8 mm

the expansion of the primary flow was more sufficient

the expansion length was longer

the expansion angle was smaller

and the entrainment ratio was improved. A further increase in the nozzle distance to 10 mm contributed to a larger expansion angle as well as a low entrainment ratio and pressure recovery ratio. From the results

the optimal NXP is in the range of 6–8 mm for the ejector under the operating conditions of this study. The results of this study contribute to a better understanding of the internal flow mechanism of the ejector and help to improve its design theory.