# Development of Hybrid Airlift-Jet Pump with Its Performance Analysis
## 5 Results and Discussion
### Performance and Efficiency of Hybrid Pump  
Figure 9a,b shows the average mass flow rate of the water versus the average mass flow rate of the air for all of the cases and the average mass flow rate of the water versus the water volume fraction at the water inlet for the hybrid cases, respectively. As shown in Case No. 1, the mass flow rate of water is zero, implying that the airflow is not sufficiently strong to pump the water to 0.9 m high. For the other cases, the water mass flow rate increases with the air mass flow rate. In Cases No. 5-8, which are set to simulate a shorter suction height of 0.4 m, the air mass flow rate does not change enormously in the same air inlet boundary condition, while the water mass flow rate is increased significantly in comparison with Cases No. 1-4. This relatively larger mass flow rate is due to the less work required to obtain gravitational potential energy with almost the same energy from the air flow. In the hybrid  
Figure 8: Comparison of predicted water flow rate with measured data according to air inlet pressure. pump, Cases No. 9-18 where the jet and airlift parts operate together are also shown in Figure 9a. When the volume fraction of water is set to be 0.5 at the water inlet (Cases No. 9-12), it shows a similar mass flow rate in Cases No. 5-8, which represent a shorter pipe suction length. The similarity here is considered to be related to less work required in the suction pipe owing to the lower mixture density or shorter suction height. When the hybrid pump case is performed with a shorter suction pipe length (Case No. 13), a more significant increase in the water mass flow rate is achieved. For the hybrid pump cases with different volume fractions of water (Cases No. 14-18), their water mass flow rates increase as the water volume fraction decrease to the value of 0.1; when the water volume fraction is further reduced to below 0.1, the water mass flow rate decreases, that is, the water mass flow rate in Case No. 14 is less than that in Case No. 15. The maximum water mass flow rate is achieved through Case No. 13, with a value of 0.21 kg/s. The effects of the water inlet volume fraction and the water suction height on the water mass flow rate can be seen in Figure 9b. To compare the performance of the pump operating under different conditions more quantitatively, the efficiency of the hybrid airlift-jet pump is defined as:  
\[\eta=\frac{P_{out}}{P_{in}}=\frac{(H_{2,w}-H_{3,w})\dot{m}_{w}}{(H_{1,a}-H_{2, a})\dot{m}_{a}} \tag{11}\]  
where \(\dot{m}\) represents the mass flow rate of the fluid; the subscripts \(w\) and \(a\) represent the water and air, respectively; the subscripts 1, 2, 3 denote the monitoring locations, as shown in Figure 10; \(H\) is the total head of water or air in a certain location, which can be expressed as:  
\[H=\frac{P}{\rho g}+\frac{v^{2}}{2g}+h \tag{12}\]  
Equation (11) is typically used for assessing the performance of the jet pump; however, it is also suitable for the hybrid pump. With only normal-pressure air being released at the water inlet, the additional input power is sufficiently small to be ignored owing to its low kinetic energy and small mass flow rate at the water inlet. Therefore, the equation is still valid provided that the state for each phase is correctly monitored at every boundary. However, note that Equation (11) needs to be corrected if the airlift part is modeled in more realistic ways: for example, the water volume fraction boundary condition is replaced with air-injection with higher pressure. Figure 9: Comparison of mass flow rates of hybrid airlift-jet pump in various operating conditions: (**a**) all cases; (**b**) airlift-jet hybrid pump cases. The predicted efficiency, the air mass flow rate, and the water mass flow rate in each case are shown in Figure 11. Figure 11a shows a similar relationship to that in Figure 9a. A higher efficiency is generally achieved when more air is injected as the air inflow in Cases No. 1-8, while the efficiency decreases in higher airflow rates for Cases No. 10-12.