## 3 Results and Discussion  
### Nonequilibrium Phase Change Characteristics in Steam Ejectors  
The nonequilibrium phase change process in the steam ejector was analyzed through the distribution of the steam subcooled degree and steam wetness fraction on the axis of the steam ejector. The subcooled degree is defined as the difference between the steam pressure and the saturation temperature. The distribution of the subcooled degree can reflect the variation trend of the steam thermodynamic state well. Figure 4 shows the distribution of the subcooled degree of the steam ejector axis under different \(P_{m}\). It can be seen from the figure that the subcooled degree increased continuously after the primary flow passed through the nozzle throat. The droplet released latent heat of condensation in the process of growth based on condensation nuclei and the primary flow suddenly dropped. The inflection point of the subcooled degree is called the Wilson point [34]. When the primary flow passed through the nozzle outlet, a series of shock waves alternating between compression waves and expansion shock waves were generated in the mixing chamber. When the primary flow passed through the compression shock wave, the subcooled degree was negative; that is, the primary flow was in a superheated state. When the primary flow passed through the expansion shock wave, the subcooled degree increased further and the steam was in the nonequilibrium state of supercooling. When the primary flow was mixed with the secondary flow, a choking effect occurred in the mixing chamber. At this time, the subcooled degree of the primary flow reduced from 3 K to \(-18\) K. This meant that the choking effect caused the mixed flow to overheat. After entering the diffuser, the mixed flow accelerated the expansion and the subcooled degree increased. Then, under the choking effect of the shock waves in the diffuser, the subcooled degree changed from positive to negative and the mixed flow changed from the supercooled state to the superheated state.  
The distribution of the wetness fraction can reflect the process of the phase change in the steam ejector. A decrease in the wetness fraction means the droplet evaporates, while a rise in the wetness fraction means the droplet condenses. The distribution of the wetness fraction along the steam ejector axis under different \(P_{m}\) is shown in Figure 5. It can be seen from the figure that the wetness fraction increased rapidly at the Wilson point in the nozzle, while the wetness fraction decreased when the primary flow passed through the compression shock wave in the mixing chamber and increased when it passed through the expansion shock wave. According to the analysis in Figure 4, when the primary flow was in an overheated state in the compression shock wave, the droplet absorbed the heat and evaporated, resulting in a decrease in the wetness fraction. In addition, when the primary flow was in a supercooled nonequilibrium state in the expansion shock wave, the  
Figure 4: Subcooled degree distribution along the steam ejector axis under different \(P_{m}\).  
droplets continued to condense and release the latent heat of the condensation, resulting in an increase in the wetness fraction. The mixed flow continued to expand after entering the diffuser and the condensation of the droplets increased the wetness fraction. After the mixed flow passed through the shock wave, a large number of droplets evaporated and the wetness fraction dropped sharply until it reached zero.