| Under the condition of bubble inflow,when the incoming air bubbles accumulate to a certain extent in the centrifugal pump impeller,the performance of the centrifugal pump will suddenly drop,and the surging will occur.In severe cases,the impeller passage will be blocked and the gas locking will be generated.This not only greatly reduces the service life of the centrifugal pump,but also affects normal production.The occurrence of pump surging is related to the gas-liquid two-phase flow characteristics in the centrifugal pump.In particular,the flow pattern,bubble motion and morphological changes in the impeller have an important influence on the performance of the centrifugal pump.Therefore,this paper establishes a centrifugal pump visual observation platform,studies the flow pattern of the centrifugal pump impeller and its bubble change process,and obtains the gas-liquid two-phase flow characteristics in the centrifugal pump impeller and its influence on the pump performance.The main research work and research results are as follows:(1)The gas-liquid two-phase flow pattern in the centrifugal pump impeller was obtained,and the corresponding flow pattern map was drawn.The influence of inlet parameters on the flow pattern was revealed.There are four typical flow patterns in the impeller,such as bubble flow pattern,agglomerated bubble flow pattern,gas pocket flow pattern,and separated flow pattern.It is found that the inlet volume void fraction is the most direct factor leading to the transformation of the flow pattern;as the liquid flow rate and rotational speed increase,the area of gas occupying the impeller passage decreases,and the flow pattern changes at a certain void fraction.(2)The bubble dynamics behavior of the four flow patterns was ascertained,and the bubble shape change process was summarized.It is observed that the bubble flow path in the impeller tends to move from the suction side of the blade at inlet to the pressure side of the blade at the outlet.The bubble dynamic behavior directly leads to the change of the flow pattern in the impeller;with the increase of inlet volume void fraction,the tendency of bubble coalescence in the impeller passage increases,and the bubble morphology changes accordingly.Finally,the flow state in the impeller changes near the entrance of the impeller,which affects the performance of the pump.(3)The influence of gas-liquid two-phase flow characteristics and inlet parameters on pump performance was revealed,and the effectiveness of the existing pump surging prediction model was verified.The results show that the inlet volume void fraction is the most direct factor leading to the deterioration of pump performance,and the increase of liquid flow rate and rotational speed has a positive impact on pump performance.Combined with experimental data,the comparison of different surging prediction models found that Zhu’s surging prediction correlation is more accurate and more suitable for predicting the initiation of surging point. |
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