## 3 Results and Discussion  
### Structural Division of Shock Wave Structure in the Ejector  
The efficiency of the ejector is mainly determined by the degree of the mixing process between the primary fluid and the secondary fluid, as discussed in Part 1. Another important aspect affecting the pumping performance of the ejector is the complex flow characteristics of the steam ejector produced. Among these flow characteristics, the shock wave structure is extremely complex and its structure is one of the factors to determine the pumping performance of the steam ejector [40]. However, there is still a less thorough understanding of the whole shock wave structures in detail. This section will analyse and discuss the shock waves inside the steam ejector. The Mach number contour of the flow field and the static pressure distribution curve of the wall and the axis of the ejector are shown in Figure 3. The whole shock wave structure in the steam ejector can be clearly observed. The static pressure at the axis of the mixing chamber fluctuates up and down due to the existence of a series of shock waves in the mixing chamber and the throat sections. The zone ranges from the beginning point A of the shock wave to the point B where the two static pressure curves coincide is called the shock train region which is separated by the choking position of the secondary fluid. The range of this region is the length of the primary fluid jet core as described in Part 1. The pressure along the wall of the pseudo-shock region changes relatively smoothly, but the pressure along the axis continues to oscillate and its amplitude gradually decreases until the point B. The zone which ranges from the first coincidence point A to the second coincidence point C is called the co-velocity region. The pressures and the velocities are constant and the two streams begin to mix with each other. The shock train and the co-velocity region are collectively referred to as a pseudo shock region [43] while the oblique-shock region consisting of a single normal shock wave and a series of oblique shocks [40], and the range of which is from the position of the normal shock wave to the coincidence point C.  
From the Mach number cloud diagram of the steam ejector in Figure 4a, it can be clearly seen that three types of shock waves exit in the whole flow field. One type is the shock train consisting of several diamond waves both in the mixing chamber and the throat sections as displayed in Part 1, the other type is a single inviscid normal shock wave in the subsonic diffuser section. The last type is the oblique shock following with the normal shock. Figure 4a displays the Mach number counter of the ejector when the primary fluid pressure, secondary fluid pressure and the back pressure are 0.36 MPa, 2330 Pa and 3500 Pa, respectively. As indicated by the Mach number distribution along the radial distance shown in Figure 4b, the larger change of the velocity gradient begins at 0.50m distance along the wall. When the distance is greater than 0.50 m on the X-axis, greater velocity fluctuation occurs near the wall showing that the normal shock wave starts to change into the oblique shock waves [40]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Properties**} & **Dynamic** & **Thermal** & **Specific** & **Molecular** \\  & **Viscosity** & **Conductive** & **Heat Capacity** & **Weight** \\ \hline \multirow{2}{*}{Value} & \(1.34\times 10^{-5}\) & 0.00261 & 2014.00 \(\mathrm{J}\) & 18.01534 \\  & kgm\({}^{-1}\)s\({}^{-1}\) & Wm\({}^{-1}\)K\({}^{-1}\) & kg\({}^{-1}\)K\({}^{-1}\) & kgkmol\({}^{-1}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Properties of the working fluid used in the simulation. \begin{table}
\begin{tabular}{c c} \hline \hline \multicolumn{2}{c}{**Operating Condition**} & **Value** \\ \hline Primary fluid pressure & 360,000 Pa \\ Secondary fluid pressure & 2330 Pa \\ Back pressure & 3500 Pa \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The operating conditions of the numerical simulation.