Airlift Pumps with Annulus Risers: An Experimental Investigation

Abstract

Airlift pumps are used in many industries. In these pumps, the performance is strongly affected by the geometrical design conditions. In this study, the performance of an airlift pump is experimentally evaluated for both circular and annulus pump risers. An airlift pump operating under air-water two-phase flow conditions was tested using a dual pump injector and for a constant submergence ratio. Capacitance sensors are used to measure the instantaneous void fraction through the pump riser, while high-speed images are analyzed to identify the interfacial structures of the air-water two-phase flow patterns through the pump risers. The results show that the water flow rate and efficiency of the pump for both risers are strongly dependent on the flow-pattern. In the annulus riser, higher liquid flow rates and pump efficiency are achieved at low gas flow rates, where slug pattern exists, while for the circular riser, the pump performs better at higher gas flow rates. Also, void fraction was found to be higher in the annulus riser for the entire range of gas flow rate due to the smaller cross-sectional area and the faster gas phase velocity through this area. Moreover, in the annulus riser, the Taylor bubble exhibited rotational motion around the pipe axis while moving upward. The length of Taylor bubbles in the pump riser was found to be longer and move with higher velocity and frequency in the case of the annulus riser, which is contributing to the better pump performance at low air flow rates.