Investigation On Gas-Liquid Two-Phase Flow Char Act-Eristics Of Centrifugal Pump Based On CFD-PBM Coupling Model

On the condition of bubble inflow,the bubbles in the flow channel of the impeller of the centrifugal pump are aggregated and broken.When the bubbles accumulate to a certain extent in the flow channel,an air pocket is formed,thereby affecting the head and efficiency of the centrifu gal pump,resulting in degraded performance of the centrifugal pump,and even affecting the safety and stability of the entire system.Therefore,it is important to study the flow characteristics in a centrifugal pump on bubble inflow conditions.In this paper,on bubble inflow condition,the characteristic of gas-liquid,two-phase flow in a centrifugal pump is studied by numerical simulation,and the accuracy of the numerical simulation method is verified by experiments.The effects of inlet gas volume fraction,liquid phase flow rate and rotational speed on the head and efficiency of the centrifugal pump are investigated.The main results are as follows:(1)The numerical simulation method of gas-liquid two-phase flow of centrifugal pump based on CFD-PBM(CFD-Population Balance Model)coupling model is established.Compared with the numerical method based on Eulerian-Eulerian model,the simulation results agree well with the experimental results.Especially when the gas volume fraction is higher,it can more effectively simulate the dynamic behavior of bubbles in the centrifugal pump,such as coalescence,crushing and separation,and then accurately predict the "Surging" characteristics of the pump.(2)The influence of parameters such as inlet gas volume fraction,liquid phase flow rate and rotational speed.on the head and efficiency of the centrifugal pump is obtained.The head and efficiency of the centrifugal pump decrease with increasing inlet gas volume fraction,and increase with increasing rotational speed.When the inlet gas volume fraction increases from 3%to 5%,the air mass formed by bubbles stays in the impeller flow channel and can’t be discharged with the liquid phase.So the centrifugal pump head has a sudden drop phenomenon,that is,"Surging" occurs.In addition,the head and efficiency of the centrifugal pump first decrease and then increase as the liquid phase flow increases.(3)The variation of the external characteristics such as the head and efficiency of the centrifugal pump is directly related to the in-stu gas void fraction and bubble size distribution in the pump.As the inlet gas volume fraction increases,the in-stu gas void fraction of the centrifugal pump gradually increases,and the proportion of large bubbles increases.The existing in-stu gas void fraction and bubble size prediction models are verified.Among them,the Estevam model and the Pineda model have better adaptability when predicting the in-stu gas void fraction,and the error is no more than ±20%.The relative error of the bubble size predicted by the Gamboa model is no more than ±30%,and the larger the inlet gas volume fraction,the smaller the prediction error.