## 4 Results and Discussion  
### The Influence of the Primary Fluid Temperature  
As can be seen from the variation of the entrainment ratio with the primary fluid temperature in Figure 9. The operating condition was the secondary fluid temperature, and the back pressure is 15 \({}^{\circ}\)C and 3000 Pa, respectively, which the primary fluid temperature varies from 134 \({}^{\circ}\)C to 146 \({}^{\circ}\)C. The maximum value of the entrainment ratio is 0.69 as the primary fluid temperature is 138 \({}^{\circ}\)C. The entrainment ratio increases with the increasing of the primary fluid temperature when it is less than 138 \({}^{\circ}\)C. On the contrary, when the temperature is higher than 138 \({}^{\circ}\)C, the entrainment ratio gradual declines. In the condition of the constant geometry of the eject, there exists a primary fluid temperature which optimizes the entrainment ratio. The static pressure lines of the flow structure are as shown in Figure 10 that the length of the shock train and the shock-mixing layer are almost the same. It indicates that these two flow characteristics are less affected by the primary fluid temperature. There is no significant difference inside the mixing chamber and diffuser sections when the temperature changes. Though the Mach number changes a lot at the inlet of the throat section, the shape of the primary fluid jet core is also similar. The local peak value of the normal shock wave increases with the temperature increasing. Figure 8: Flow structure partition under the influence of the shock-mixing layer. Figure 9: The variation of the entrainment ratio with the primary fluid pressure. With the increase of the primary fluid temperature, the position of the normal shock wave gradually moves from the outlet of the throat section to the inlet of the diffuser section and the intensity of the normal shock wave is enhanced (see Figures 10 and 11). Thus, the ability to resist the interference of the back pressure is significantly improved. Only when the normal shock wave is generated in the diffuser section, the ejector will work in double-choking flow and operates in a normal working state [45]. As mentioned before, the choking zone is an area that the static pressure and velocity were constant. As can be seen from Figure 11, the length of the choking zone changes with the primary fluid temperature. The length of the choking zone reaches the maximum value of 86 mm when the temperature is 138 \({}^{\circ}\)C. As the length of the choking zone increases, the inducing zone which is in front of the choking zone is almost the same while the discharge zone after choking zone is shortened. Compared with Figure 9, it is found that the length of the choking zone is a positive linear correlation with the entrainment ratio and the length of the choking zone directly affects the efficiency of the ejector. As the aspect of the energy transmission, the inducing zone and the choking zone were the main areas where the kinetic and the internal energy exchanges between the primary fluid and the secondary fluid. The two zones are including in the energy exchange progress. The results illustrate that the pumping performance of the ejector would be directly determined by the length the energy exchange progress. The longer length of the energy exchange progress, the higher the efficiency of the ejector would be. The length of the choking zone should be increased as the length of the discharging zone should be reduced to improve the pumping performance of the ejector. When the primary fluid temperature is too high, there will be a velocity reflux flow at the position of the nozzle outlet and a part of the kinetic energy would be lost as shown in the dotted line in Figure 11. It causes the kinetic energy of the primary fluid entering the choking zone reduced, and the entrainment ratio decreased. Although the length of the choking zone is much longer at 146 \({}^{\circ}\)C than at 134 \({}^{\circ}\)C, the entrainment ratio of the two is similar, which are 0.572 and 0.5684, respectively.