Modelling the performance of the non-straight up-riser airlift pump

This study presents a model to evaluate the effects of geometric discontinuities, including enlargement, contraction, and bends, in the up-riser pipe on airlift pump performance. The airlift pump system is discretised into segments, and the governing continuity, momentum, and energy equations are applied to each section, incorporating appropriate correlations for slip ratio, friction factor, and loss coefficients. The resulting system of equations is solved numerically using a computer programme. The model is applied to configurations involving one-step and two-step enlargement and contraction located at ¼, ½, and ¾ of the up-riser height, as well as to bent up-risers with joint lengths of 0, D, and 2D, where D is the up-riser diameter. The proposed model is valid for bubbly, slug, and churn flow regimes. However, it shows limitations in predicting airlift pump performance in the annular flow regime, where the pump typically operates outside its optimal range. The analytical model was further employed in a parametric study, which revealed that increasing both the diameter and relative length of the enlarged pipe section consistently enhances pump performance, although it also increases the minimum air mass flow rate required to initiate water lifting. In addition, the results indicate a strong sensitivity of pump performance to the bend loss coefficient; in some cases, doubling this coefficient can reduce water throughput by up to 50%.