To study the variation of internal flow in self-priming process of the self-priming centrifugal pump, a flow visualizable transparent self-priming centrifugal pump prototype was designed. The pressure, flow rate and rotational speed, etc., were recorded in the self-priming process of the pump with Labview virtual instrument in time domain, and the influence of rotational speed on the outlet pressure and self-priming time of the pump was investigated. Meanwhile, the air-water two-phase flow patterns in the key components of the pump were shot with a high-speed camera at various stages of the self-priming process, and transient variations of the two-phase flow in the pump were analyzed. The results show that the self-priming process of the pump can be divided into three stages in terms of the variations of pressure and flow rate with time, i.e., start-up, stable and sudden change stages. This feature can also be observed in the outlet pressure profiles at different rotating speeds. In the stable self-priming stage, the faster the impeller rotating speed, the larger the fluctuation amplitude in the outlet pressure, the higher the final stable pressure and the shorter the self-priming time. Bubble splitting phenomenon exists in the volute and impeller during the self-priming process. Firstly, a single large bubble is gradually elongated into a bubble in dumbbell shape. Then the connecting channel in the middle of the bubble disappears and the bubble is split into two small ones to promote air separation and complete the self-priming process.
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