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

离心泵最初是用来处理单相液体的。在两相流条件下运行的泵通常会降低其叶轮的工作效率和泵送活动，因此，必须非常小心地注意避免空气夹带。近年来，为了核反应堆的安全性分析或化工厂污水泵的高效利用，需要泵在气液混合环境下工作，从而促进了这方面的研究。本课题对一种径向流泵在进气条件下进行了试验研究，探讨了其性能和流态变化的机理。为了预测离心泵叶轮内空气-水两相流动的特性，提出了一种基于气泡流动模型的三维数值计算方法。如果假定混合流体是均匀的气泡流，沿叶轮通道的特征长度夹带细气泡，则混合流体的运动方程用液相的运动方程表示，其速度用准调和方程表示。利用有限元法求解方程得到速度，并对气泡在该流场中的运动方程进行数值积分得到空隙率。所得结果在气泡流型范围内与实验结果吻合较好。

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.