平衡孔直径对离心泵小流量工况空化特性影响

为研究小流量工况低比转速离心泵的空化特性，以一台降速后的IS80-50-315型离心泵为试验对象，专门设计了更换平衡孔直径的装置，当平衡孔直径等于4、6、8和11mm时分别对0.4Q_d、0.5Q_d、0.6Q_d和0.8Q_d这4个工况进行测试并分析。结果表明，叶轮平衡孔直径增大，泵扬程减小，效率下降。小流量工况下，随空化数的减小，不同平衡孔直径叶轮所受扭矩与泵扬程均出现不同步的陡降，且扭矩有明显的匍匐变化，这主要是由蜗壳和叶轮之间的动静干涉引起的；同一空化数下加大平衡孔直径，扬程系数增加，叶轮轴向力减小，离心泵的抗空化性能增强；同一平衡孔直径下流量越小，离心泵越不易发生空化，但随着离心泵内空化的产生和发展，泵腔内液体压力的下降速率先增大后减小，叶轮轴向力具有先趋于平坦后急剧增加的规律。从抑制空化和减小轴向力的角度，提出平衡孔直径在6~8mm较为合适。

Effects of balance holes diameter on cavitation characteristics of centrifugal pump under low flow rates

In order to investigate the cavitation characteristics of low specific speed centrifugal pumps under low flow rates, rotation rate reduction IS80-50-315 centrifugal pump is taken as the experimental object, and a device is especially designed so as to replace the balance holes of different diameters. Cavitation characteristics were measured and analyzed at 0.4Q_d, 0.5Q_d, 0.6Q_d, and 0.8Q_d when the balance hole diameter is equal to 4, 6, 8, and 11mm. The results show that with the increase of the balance hole diameter, the pump head and its efficiency reduce. Both the torque-drop and head-drop curves of impellers with different balance hole diameters have the same shape of dropping and the torque-drop has obvious creeping change, with the corresponding break-down points occurring asynchronously under the low flow rate condition. It is caused by the rotor-stator interaction between the volute and the impeller. When the balance hole diameter increases under the same cavitation number condition, the head coefficient increase, the axial forces acting on impellers decrease and the anti-cavitation characteristics of centrifugal pump are enhanced. The slower the flow with the same balance hole diameter is, the harder the cavitation of centrifugal pump becomes. But the descent speed of the fluid pressure in the pump chamber of the centrifugal pump increases first and then decreases, the axial forces acting on impellers tend to flat and then increase sharply with the development of cavitation. In order to suppress cavitation and decrease the axial thrust, it is proposed that the most appropriate balance hole diameter is in the range of 6mm to 8mm.