Research On The Influence Of Balance Hole On The Performance Of Centrifugal Gas-liquid Multiphase Transport Pump

The centrifugal pump will experience performance degradation and unstable operation due to the accumulation of gas-phase under gas-liquid two-phase conditions.The balance hole can effectively reduce the axial force on the impeller and improve the pump’s operational stability.In this paper,the flow characteristics of a centrifugal pump with different inlet gas volume fraction are investigated by using numerical simulation method,and the influence of balance hole parameters on the performance of centrifugal pump is studied.The mechanism of the effect of the balance hole on the performance of the pump is expounded.The main research contents and conclusions are as follows:The influence of the inlet bubble size on the accuracy of the numerical simulation.It is found that when a single bubble size is used for the simulation,the numerical simulation results and the experimental results have a larger error under the high gas void fraction.The inlet bubble size for numerical simulation with different inlet gas content at design flow rate is checked based on the test head,and a mathematical model between the inlet gas volume fraction and bubble size is established.On this basis,the influence of gas volume fraction on the external characteristics of the multiphase pump,the gas distribution in the impeller and the axial force on the impeller is studied.The results show that the head and efficiency of the pump gradually decrease with the increase of the inlet gas volume fraction.The gas-phase mainly accumulates at the position of the blade pressure surface near the front cover.And the area of the gas-phase accumulation increases with the increase of the inlet gas volume fraction,and moves from the inlet to the outlet of the impeller along the blade pressure surface.The axial force gradually decreases with the increase of the inlet gas volume fraction.Especially,the magnitude of the axial force suddenly decreases under the large flow rate condition.At a mixed media flow rate of 480m3/h and an inlet gas volume fraction of 5%,the axial force on impeller is reversed.A parametric study of the balance hole is conducted.The influence of the balance hole radial position,the circumferential position and the balance hole diameter on the external characteristics,the distribution of the gas-phase inside the impeller and the axial force are explored.The study shows that when the balance hole is located in the gas-phase gathering area,the balnce hole can effectively improve the gas-phase gathering phenomenon in the impeller and enhance the pump performance.when the balance hole is outside the gas-phase gathering area,the backflow from balance hole leads to turbulent flow in the impeller,which increases the impeller hydraulic loss and causes the pump performance to drop.The axial force is more influenced by the radial position of the balance hole and less influenced by the circumferential position of balance hole.When the center position of the balance hole moves from the impeller inlet to the outlet,the effect of the balance hole on the axial force is gradually weakened.The larger the diameter of the balance hole,the effect of improving the phenomenon of gas-phase gathering in the impeller and balance the axial force is more obvious,but too large diameter will cause a great increase in the impeller hydraulic loss.When the balance hole diameter is between 6mm-12mm,the comprehensive performance of the pump is effectively improved.The optimal balance hole parameters are selected and the mechanism of the influence of balance hole on the performance of gas-liquid two phase transfer pump was investigated.The results show that the blance hole will lead to the degradation of the pump performance when the gas volume fraction is small,while the balace hole can effectively improve the pump performance under high gas volume fraction.At small gas volume fraction,the unsteady flow in the impeller is aggravated by the backflow of the balance hole,which increases the hydraulic loss of the pump.At high gas volume fraction,the balance hole improves the phenomenon of gas phase aggregation in the impeller,improves the static pressure of the blade surface at the impeller outlet position,and reduces the hydraulic loss in the impeller.The balance hole can significantly improve the gas phase distribution in the impeller,and the closer to the center of the balance hole,the better the improvement effect,while the position far from the center of the balance hole the gas phase distribution is basically unaffected.