Gas–liquid separation mechanisms and bubble dynamics in a helical axial multiphase flow pump

To clarify the mechanism of gas plugging caused by gas–liquid separation in a helical axial multiphase flow pump under two-phase conditions, the flow pattern, bubble distribution, and evolution in the pump were studied by high-speed camera technology. It is found that the gas phase presents four different forms with different inlet gas volume fractions: isolated bubble flow, linear bubble flow, airbag flow, and emulsion flow. The increase in inlet gas volume fraction promotes the aggregation of bubbles and changes the flow pattern inside the impeller. This change can be alleviated by increasing the rotational speed to promote bubble breakup. In addition, the probability density function of the equivalent diameter of the bubble in the impeller obeys the lognormal distribution, and the equivalent diameter ranges from 0 to 4 mm. The equivalent diameter of the bubble is proportional to the inlet gas volume fraction and inversely proportional to the rotational speed. The bubble behavior is unstable, and it is easy to agglomerate at the inlet and outlet of the impeller to form large bubbles, which leads to a decrease in pump performance. This study provides a scientific basis for the optimal pump design and is of great significance for preventing gas plugging.