In this paper

the motive nozzles of a CO2 ejector with a diverging angle ranging from small to large (0.076°

0.306°

and 0.612°) were investigated. Coupled models for the homogeneous equilibrium (HEM)

delayed equilibrium (DEM)

and wall friction model were presented and compared with the experimental data from related literature to analyze the dominant effects of the two flow mechanisms

non-equilibrium phase change

and wall friction on the delayed expansion process in the nozzle at corresponding angles. The results showed that within the ranges of this study

wall friction was the dominant mechanism of the delayed expansion process in the nozzle with a small diverging angle at the θ1 of 0.076°. Furthermore

the non-equilibrium phase change was the dominant mechanism in the nozzle with a middle diverging angle at the θ2 of 0.306°. In addition

the expansion process of the two-phase flow in the nozzle is close to the isentropic process for the large diverging angle at the θ1 of 0.612°. It is necessary for the design and optimization of the nozzle to choose a reliable model considering the dominant mechanism. When the diverging angle is small

the simulation results of the DEM coupled with a friction model indicated that the flow could choke the downstream of the minimum-area throat; this is verified by our experimental results. In addition

the critical mass flow rate predicted by the above model was lower than those of the HEM and DEM. The critical mass flow rates predicted by the three models indicated a barely noticeable difference for the larger diverging angle