# Development of Hybrid Airlift-Jet Pump with Its Performance Analysis
## 1 Introduction
The typical flow pattern in airlift pumps changes with the mass quantity [18], and the best efficiency is likely to occur in the slug or slug-churn flow pattern [17; 19]. Further, the effects of liquid properties [20], pipe geometry [17] or gas-injection methods [21; 22] on the performance of airlift pumps were investigated. Indirect pumps, such as the jet and airlift pumps, have not been used frequently due to their less efficiency than the direct type of pumps. However, the efficiency of the direct types of pumps strongly depends on the gap distance between an impeller and its housing. As the gap distance decreases, the efficiency of direct pumps also increases. Modern direct types of pumps keep the distance very small due to the advanced modern manufacturing technology, but the smaller distance increases the possibility that some particles in liquid block the gap and eventually cause the failure of the pump. The indirect pump can operate on such ill-conditioned liquids without suffering from such problems. In this respect, the indirect types of pumps are more durable than the direct pumps. To develop more efficient designs of indirect pumps and thus to increase their applicability in water pumping applications, the concept of hybrid airlift/jet pump is newly proposed in the preceding patent [23]. Our aim is to develop the baseline design of the hybrid airlift-jet pump and to assess its validity in terms of its performance and efficiency. The performance and efficiency characteristics of hybrid airlift-jet pumps are investigated by numerically solving the compressible unsteady Reynolds-averaged Navier-Stokes equations with a cavitation model. For simplicity, the operating condition of the airlift part is considered using the inlet boundary conditions of water. Altogether, eighteen simulation cases that are designed to represent the various operating conditions of the hybrid pump are investigated: the former eight cases belong to the operating condition of only the jet pump with different air inlet boundary conditions and the latter ten cases belong to the operating conditions of both the airlift and jet parts in the hybrid pump with different air and water inlet boundary conditions. The performance and efficiency curves of the hybrid pump are compared for each case. For further detailed investigations into the flow characteristics, the pressure and velocity distributions of the mixture in a primary pipe are compared. The periodic fluctuation of the secondary flow in the mass flow rate is found and analyzed. In Section 2, the baseline design of a hybrid airlift-jet pump is schematically presented with its relevant operating principle. In Section 3, the governing equations and the numerical methods are described. In Section 4, the detailed geometry of the pump and its computational mesh are presented with the detailed boundary conditions. In Section 5, the validity of the numerical method is confirmed by the comparison of the prediction results with the measured ones. Subsequently, the numerical results and discussions are presented to assess its performance and efficiency by investigating the detailed flow characteristics. The conclusion is presented in the final section.