## 4 Results and Discussion
This is attributed to raising the water mass flow rate, which magnifies the condensation occurrence around the upper region and hence the static pressure decreases due to phase change. The critical flow  
The turbulent intensity and kinetic energy at a point measure the degree of interactions and interruption due to fluids mixing. Figures 8 and 9 record the turbulent values due to mixing the water liquid with the side mixture at the tube upper region. The turbulent intensity and kinetic energy increase with air mass flow rate until \(\dot{\mathrm{m}}_{\mathrm{a}}=0.002\) kg/s with a water to air mass ratio of 1000 and water mass flow rate of 2 kg/s, as depicted in Figures 8a and 9a. Increasing the water mass flow rate to 4 kg/s has no significant effect on these turbulent values at the tube upper region as, by increasing the water liquid mass flow rate, the side entrained mixture is directed to flow down the tube. So, the generated turbulent values due to the mixing process in Figures 8 and 9 are less noticeable at the tube upper region at water mass flow rates of 4 kg/s compared to 2 kg/s. That means that working at a water siphon mass flow rate of 2 kg/s requires a water/air mass ratio of 1000 or less for avoiding system flow discontinuity. This can be ensured by tracking the flow velocity inside the upper region at the same operational conditions as demonstrated in Figure 10. The flow velocity rises with increasing the air mass flow rate until a mass ratio of 1000 then it recedes, and this inverted tube breaks down water siphon flow at a vapor mass ratio of 0.5, as shown in Figure 10a. Figure 6: Effect of side air on the vacuum pressure at inverted U-tube tip. Figure 7: Effect of air and vapor mass flow rates on the static pressure generation in the tube upper region. The effect of flow mass ratios of water, water vapor, and air on the static pressure contours are visualized in Figures 11-14. Low values of air and vapor flow rates satisfy the minimum pressure inside the U-tube, see Figure 11. On the other side, raising the side mixture volume ratio to 0.7 with  
Figure 8: Effect of air and vapor mass flow rates on the turbulent intensity in the tube upper region. Figure 10: Effect of air and vapor mass flow rates on the flow velocity in the tube upper region. Figure 9: Effect of air and vapor mass flow rates on the turbulent kinetic energy in the tube upper region. preserving the vapor mass ratio to be 0.1 increases the static pressure at the top of the U-tube as demonstrated in Figures 11 and 12. Raising the vapor mass ratio from 0.1 to 0.5 with maintaining the side mixture at 0.2 reduces the static pressure generation along the inverted U-tube as depicted in Figures 11 and 13. Meanwhile, increasing both ratios of water and air magnify the static pressure inside the considered tube, but water vapor has the noticed effect on preserving the lowest static pressure as preferred for this tube operation compared to full side mixture effect, as shown in Figures 12 and 14. This means that more condensation, due to increasing the vapor flow rate, enhances the present desired operations of this U-tube and it magnifies the required induced vacuum. The effect of flow mass ratios in the tube on the side air distribution is shown in Figures 15-18. Increasing the main water flow rate moves the side entrained air to flow downward, not to the suction region in the upper part of the U-tube. This is attributed to force balancing among the inertia of water flow and gravity with the force due to flow suction in the upper portion of the tube. So, reducing the force due to flow suction by magnifying the resulted force due to flow inertia weakens the entrainment operation in the inverted U-tube, as expected above in Figure 9. The flow inertia is a function of the flow velocity, which is determined by the water flow rate. This finding ensures that the relation between the flow rates of water in the tube and water vapor in the side mixture controls the entrainment process of the tube.