Distribution and motion characteristics of bubbles in a multiphase rotodynamic pump based on modified non-uniform bubble model

Abstract

Multiphase rotodynamic pumps are important equipment that transport gas-liquid mixtures in offshore oilfields, suggesting it is necessary to investigate the flow characteristics in such pumps. In this study, the Eulerian two-fluid model is solved to obtain the bubble distribution in the pump, while the non-uniform bubble model is used to predict the break-up and coalescence of bubbles. The gas cavity equation is introduced to capture the rapid coalescence of bubbles near the suction side of the impeller blades, and the interphase forces in the cavities are modified. Compared with the experimental measurements for the gas volume fraction and bubble size, it is found that the simulations with the modification have better accuracies than without it. The effects of the inlet gas volume fraction (IGVF) on the bubble distribution are analyzed. Due to the formation of vortices, a large bubble number density is observed near the shroud of the impeller inlet, which increases with greater IGVF. The gas-liquid separation in the diffuser becomes more significant as the IGVF increases. Bubbles from the impeller inlet are observed to continuously gather near the suction side of the impeller blades. This forms a gas cavity that moves towards the impeller outlet with a low gas volume fraction. The rotor-stator interactions cause the air pockets to discontinuously move along the pressure side of the diffuser blade.