Study on Air-Water Two-Phase Flow Behaviors in Centrifugal Pumps

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Centrifugal pumps are originally used for the treament of a single-phase liguid. A pump operating under a two-phase flow condition degrades usually its impeller work and pumping activity, and hence, every careful attensions are to be made to avoid the air entrainment. Recently, relating to the safety analysis of nuclear reactors or to the efficient utilization of sewage pumps in chemical plants, it is necessitated for pumps to work under gas-liquid mixtures, which has been promoted the researches on this subject.In this research project, a redial-flow pump was tested under air admitting conditions and investigated the mechanism of the change in the performance and the flow patterns. To predict the behavior of air-water two-phase flows in a centrifugal pump impeller, a three-dimensional numerical method is proposed based on a bubbly flow model. If it is assumed that the mixtures are homogeneous bubbly flow entrained fine bubbles against a characteristic length of the impeller channel, then the equations of motion of the mixtures are represented by those of liquid-phase and its velocity is expressed as a potential for a quasi-harmonic equation. The equations are solved by use of finite element method to obtain the velocities, and the equation of motion of an air bubble is integrated numerically in this flow field to obtain the void fraction. The results obtained show good agreement with experients within the range of bubbly flow regime.