Experimental investigation of flow patterns and external performance of a centrifugal pump that transports gas-liquid two-phase mixtures

In order to reveal the mechanism of two-phase flow inside a centrifugal pump, visualization experiments were performed to investigate the gas-liquid two-phase flow patterns by using high-speed photography. Meanwhile, the external performance of the pump was measured under different conditions. The flow patterns in the suction pipe can be classified into plug flow and stratified flow distinguished by the critical inlet gas volume fraction (IGVF) of 6.2%. The critical IGVF of the pump is not obviously influenced by the rotational speed and initial liquid volume flow rate. The flow patterns in the impeller and volute can be classified into four categories with the increasing IGVF. The liquid volume flow rate has a small change in the condition of isolated bubbles flow, an obvious decrease in the condition of bubbly flow, a sharp decrease in the condition of gas pocket flow, and a gentle reduction in the condition of gas-liquid separation flow. Once the IGVF reaches the critical value, some bubbles in the volute begin to flow back into the impeller near the volute tongue. When the flow pattern transfers from gas pocket flow to gas-liquid separation flow, some bubbles in the discharge pipe flow back into the impeller. When the height of gas in the suction pipe reaches a critical value about 70 mm, bubbles sometimes flow into the volute and sometimes flow back into impeller, and the liquid volume flow rate is nearly to be zero. The differential pressure of the pump decreases with the increase of IGVF, and it decreases with the increase of initial liquid volume flow rate at the same IGVF.