## 1 Introduction
The secondary fluid started from Point B is mixed with the primary fluid along the isobar line CB and arrives in point M at the end of mixing process. Subsequently, as for the shock wave, the mixed flow reaches a subsonic condition (Point E) and it arrives in condition F after it eventually passes through the diffuser. The steam jet refrigeration cycle is applied in the ejector refrigeration system [30]. Figure 3b,d illustrates a typical one stage ejector refrigeration system, where the steam ejector is shown in Figure 3c. Based on this system, numerical studies with the consideration of spontaneous condensation of the steam ejector have also been performed to analyze the development of the primary fluid and the complicated phase change process. For example, [PERSON] et al. [31] simulated the condensation process during the nozzle, and [PERSON] et al. [32] compared the CFD modeling with an experimental test-case for the condensation. The spontaneous condensation in the nozzle of the steam ejector was studied in recent decades [33; 34; 35]. [PERSON] et al. [34] found that the steam condensation increases the flow Mach number and the ejector's performance comparison with a dry gas. [PERSON] et al. [33; 35] investigated the influences of superheating operation of the primary fluid. It was concluded that 0 K-20 K superheating for the primary fluid has a positive impact on the entrainment ratio, while superheating over 20 K was meaningless and led to energy waste. [PERSON] et al. [36] showed that the primary pseudo-shock flow gives a further downstream choking position and a higher secondary fluid flow velocity at the choking position with the wet steam model. Furthermore, [PERSON] et al. [37] applied a time-marching technique to obtain more accurate numerical predictions. This technique was proven to be effective and feasible for the two-dimensional flows of the nucleating and wet steam model in nozzles. Those studies, nevertheless, are limited to mainly focus on the individual parts of the system, i.e., the nozzle. Detailed analysis of the flow field development as well as the information about phase change within the entire steam ejector including all four major components, however, has so far not been performed. Furthermore, it is critical to have a clear study of the condensation effect inside the whole steam ejector, especially in the application of the wet steam model. Considering the above-mentioned research gap, in this article, the working process of the entire steam ejector consisting of the nozzle, mixing chamber, throat and diffuser will be considered entirely utilizing CFD simulations. In essence, key objectives of this study can be summarized by the following statements:  
1. The simulation will take advantage of a wet steam model to investigate the condensation effect on the flow behavior and steam ejector performance. 2. The numerical model will be validated against experimental data and the results will also be compared with the ideal gas model. 3. Different wall functions and turbulences models will be tested to determine the most optimized model in terms of prediction accuracy. 4. A series of simulations with different wetness operating conditions will be performed to investigate the relationship between the wetness of working flows and pump efficiency.