Mechanism study on half vaned diffuser to improve efficiency of centrifugal pump

Half vaned diffuser is widely used in compressors but rarely used in centrifugal pumps. There are few studies on the application of half vaned diffuser in centrifugal pumps, and the mechanism of half vaned diffuser reducing energy loss of pumps has not been revealed. This paper applies entropy generation theory and Ω-method to correlate external characteristics, internal flow, and entropy generation to reveal the mechanism that half vaned diffuser can move the high efficiency zone of pumps to the large flow rate and improve the efficiency. The results showed the highest efficiency is 55.07% under 0.91 times the design flow rate when vaned diffuser is used, while 56.82% under 1.13 times the design flow rate when half vaned diffuser is used. Half vaned diffuser mainly improves internal flow and reduces entropy generation of the volute by changing its own internal flow but has little influence on entropy generation of the impeller and diffuser. Compared with vaned diffuser, the interaction between cross-vane flow of half vaned diffuser and the mainstream eliminates vortex structures in the diffuser near the tongue, and the backflow in the volute and large vortex structures with blocking effect, and reduces entropy generation of pumps. End clearance can weaken rotor–stator interaction and pressure fluctuation of the gap between flow passage components, improve the flow stability and uniformity of the inlet of the diffuser and volute, balance the volute asymmetry, reduce the tongue interference, and enhance the flow capacity. So, half vaned diffuser can effectively improve efficiency and move the high efficiency zone to the large flow rate.