Numerical analysis of bubble size effect in a gas-liquid two-phase rotodynamic pump by using a bubble coalescence and collapse model

Abstract

The inlet bubble sizes and their coalescence and collapse behavior are the key factors affecting the performance and transportability of the multiphase pump. In this paper, a bubble coalescence and collapse model is applied for the simulation of a gas-liquid two-phase rotodynamic pump. The external characteristic, gas-liquid flow, phase interaction, and pressure fluctuation are analyzed using computational fluid dynamics (CFD) methods as the inlet bubble diameter d0 varies from 0.1 mm to 2.2 mm. The CFD results show that the pump’s efficiency and pressure rise decrease sharply at 0.1 mm ≤ d0 ≤ 0.4 mm, slow down at 0.4 mm < d0 ≤ 1.3 mm, and become stable at 1.3 mm < d0 ≤ 2.2 mm. The effects of inlet bubble size on flow characteristics in the impeller, such as gas-liquid separation, flow separation, vorticity change rate, and interphase force, are larger than that in the guide vane. The drag is the most significant interphase force at d0 = 0.1 mm, while the lift force plays a dominant role at d0 = 0.7 mm and 1.9 mm. The effect of the turbulent dispersion force is weakest at d0 = 0.1 mm, 0.7 mm, and 1.9 mm. Rotor-stator interaction is the key driver of the pressure fluctuation in the gas-liquid two-phase pump but is restrained by serious phase separation, flow separation, and interphase interaction at the impeller outlet. The most obvious fluctuation occurs near the guide vane inlet at d0 = 0.1 mm, 0.7 mm, and 1.9 mm. The maximum fluctuation at d0 = 0.7 mm and 1.9 mm are 5.98 times and 7.17 times that at d0 = 0.1 mm.