Research on the Effect of Impeller Reflux Balance Holes on Pressure and Axial Force of Centrifugal Pump

The size of impeller reflux holes for centrifugal pump has influence on the pressure distribution of front and rear shrouds and rear pump chamber, as well as energy characteristics of whole pump and axial force. Low specific-speed centrifugal pump with Q=12.5m3/h, H=60m, n=2950r/min was selected to be designed with eight axial reflux balance holes 4.5mm in diameter. The simulated Q-H curve and NPSH were in good agreement with experimental data, which illustrated that centrifugal pump with axial reflux balance holes was superior in the cavitation characteristic to that with traditional reflux balance holes; however, it appeared little difference in head and efficiency. Compared with experiment results, the error of pressure at monitoring points in rear pump chamber was within permission. The pressure in rear pump chamber at 0.6 times rated flow is 29.36% of pressure difference between outlet and inlet, which reduces to 29.10% at rated flow and 28.33% at 1.4 times rated flow. As the whole, the pressure distribution on front and rear shrouds from simulation results is not a standard parabola, and axial force decreased as flow rate increased. Radical reflux balance holes chosen to be 5.2mm and 5.9mm in diameter were further designed with other hydraulic parts unchanged. With structural grids adopted for total flow field, contrast numerical simulation on internal flow characteristics of reflux holes with different diameters was conducted based on momentum equations and standard turbulence model (κ-ε). It is found that axial force of pump with radical reflux balance holes 5.2mm and 5.9mm in diameter is significantly less than that with radical reflux balance holes 4.5mm in diameter, so are the head and efficiency. Better effect of axial force balance can be obtained as the ratio of area of reflux balance holes and area of sealing ring exceeds 6.