Analysis of bubble distribution in a multiphase rotodynamic pump

Abstract

Recent researches show that the pressure increment of a multiphase pump is affected by bubble size and distribution. In order to study the bubble distribution characteristics in such pumps, a novel approach describing the variable bubble size in the pump is proposed. The bubble number density equation, which has taken into account the phenomena of break-up and coalescence, is introduced into the flow simulation, and the drag coefficient is revised because of the interaction of multiple bubbles. The reliability of the approach is verified by comparison with the experiment. It was established that the bubbles move to the impeller hub due to the difference in centrifugal force between gas and liquid. Despite the high collision rate near the hub, bubble size changes little with the stirring action of the impeller. The mixture flows in a disorderly way and the bubble diameter increases due to the rotor–stator interaction. Owing to the increasing flow area in the diffuser, bubbles move to the mainstream region, and bubble size reaches its maximum owing to the flow separation near the hub. The distribution of bubbles is also analyzed under a different inlet gas volume fraction (IGVF) and inlet bubble diameter (d0). Bigger IGVF brings about a higher collision rate of bubbles, while smaller d0 makes the diffusion of bubbles easier.

Keywords

• multiphase rotodynamic pump
• bubble size
• bubble number density
• gas–liquid flow
• numerical simulation