## 4 Results and Discussion  
In the proposed framework, low energy consumption with a simple construction device for maintaining the low generated pressure for engineering applications is presented. This flow is captured using Ansys Fluent with some model adjustments. The full details for the computational model are shown in Figures 2 and 3. Furthermore, the free predicted water mass flow rate in the U-tube shown in Figure 2 is 3.72 kg/s at a water elevation difference of 75 cm between the two tanks while the mixture inlet at the side pipe is blocked. This free predicted water flow rate is a function of the elevation difference between two water levels. The main objective of the current study is to investigate the two-phase flow interactions when it encounters condensation in the considered U-tube. Besides, the effect of water flow rate ratios and the critical operational conditions are highlighted. First, the computational results are validated with the results obtained in the experimental part of the present work and with the experimental data, reported in [18] as well, for air and water two-phase flow in pipes, as shown in Figure 4. It is to be noticed here that, in carrying out the computation for validation, the values of the mass flow rate of water siphon flow and air streaming from the side pipe were taken from the present experimental record. Additionally, the air-water two-phase flow in the inverted U-tube is previously studied in [31] and the main findings encouraged the present computations. The air mass fraction in the air/water mixture is represented on the horizontal axis while the air volume fraction appears on the vertical axis. Figure 4 shows an acceptable qualitative validation for the present computational model. It is expected that the water mass flow rate affected by the siphon flow would decrease as the air and water vapor mass flow rate is raised. This is ascribed to the increase in flow resistance. The effect of side air entrainment on the water siphon flow at different water levels between tanks (\(\Delta Z\)) appears in Figure 5, as obtained by the aid of the experimental data in this work. Side air suction from the branch side tube lowers the water siphon flow rate at different water levels between tanks. This is attributed to the effect of entrained air on the vacuum pressure at the tube upper region which is found weakening the siphon flow. The experimentally recorded vacuum pressure at the inverted U-tube tip is shown in Figure 6. Side air entrained into the inverted U-tube decreases the generated vacuum pressure at its tip. The computational model is executed for the operational conditions of water mass flow rate of 2, 4, 6 and 8 kg/s with side gas mixture fraction by volume of 0.2-0.7. The water vapor fraction in the side mixture is allowed to be in the range of 0.1-0.5. The air mass flow rate effect on the static pressure in the U-tube upper region is shown in Figure 7 at various water vapor mass ratio, MR. Reducing the U-tube upper part static pressure raises the suction effect for the side mixture, which results in improving the present tube function. Increasing both air and water vapor mass flow rates elevates the static pressure in the upper part of the tube, which is undesirable. Additionally, the lowest generated static pressure can be found at a water flow rate of 2 kg/s at lower than or equal to the water/air mass ratio of 1000. For a water/air mass ratio of more than 1000, raising the water vapor flow rates magnifies the static pressure; this is attributed to increasing the water vapor flow rate at a higher air mass flow rate, which decelerates the main flow and pushes the side flow down in the tube and, hence, the condensation takes place away from the upper region. The gradient of increasing the pressure with air mass flow rate in the upper region is more pronounced at a water mass flow rate of 2 kg/s, as noticed in Figure 7a, compared to the static pressure in Figure 7b at a water mass flow rate of 4 kg/s.