Air injection methods: The key to a better performance of airlift pumps

[Display omitted] •The effect of air injection methods on the pump performance is investigated.•The effect of two-phase flow patterns and the phase interaction is presented.•The performance of pump depends on the injector design and injection method.•The pulsating air injection mode is found to control the intermittent flow pattern.•The performance is enhanced by minimizing air penetration and water reverse. This paper presents a comprehensive experimental investigation on the effect of air injection methods on the performance of airlift pumps. The effect of air–water two-phase flow patterns and the phase interaction is presented. The present airlift pump utilizes various air injectors specially designed to enable air injection radially, axially, dual (radial and axial), or with a swirl effect at the air inlet ports. In addition, two air injection modes including steadily and pulsating, at different injection frequencies, are investigated at different two-phase flow patterns. The results have shown that the performance of airlift pumps does not only depend on the design of air injector, but also on the dynamics of air injection method. The pulsating mode of air injection is found to control the intermittent flow pattern in the pump riser and consequently able to keep the pump operating within the best efficiency range. The maximum efficiency of the pulsating axial injection operating at a frequency of 1Hz has improved by 60% over that of typical steady axial injection and by 24% over that of steady dual injection. Furthermore, the performance of airlift pumps with dual injector is improved by synchronizing the injected air at both axial and radial injection ports. The improvement in this arrangement is attributed to the better utilization of available compressed air, reduction of axial air penetration and minimization of water reverse flow in the riser pipe.