Effect of the up-riser pipe diameter discontinuity on the airlift pump performance

Abstract

The present study was directed towards studying the performance of the airlift pump with variable cross-section up-riser. The effect of one-step and two-step up-riser enlargement and contraction on the performance of the pump was experimentally investigated. The two-phase flow patterns at the region of cross-section change were also visualized and discussed. The results show that for the one-step enlargement up-riser pipe, the minimum air mass flow rate required to start water flow increases as the up-riser total inside volume increases. At high air flow rates, by contrast, as the up-riser pipe average cross-sectional area increases, the pump water capacity increases. Meanwhile, the two performance curves of one-step and two-step enlargement have similar trends, but the two-step enlargement delivers higher water productivity. The preference of using multiple steps in low-to-medium air flow rate range is remarkable, as eddy losses are lower in the gradually reducing pipe. No flow pattern change appears in the expansion section of the two-step expansion riser, while the one-step expansion riser marks a flow transition from slug to churn flow patterns and from annular to churn flow patterns. A comparison between the water productivity of the one-step contraction and the two-step contraction up-risers displays that the two-step contraction exhibits a higher performance. Moreover, comparisons between enlargement and contraction configurations outline that the enlarged pipe configuration lifts larger amounts of water than the contracted configuration.