Theoretical study of a mixed pump in startup process

In this paper, based on the angular momentum conservation and energy conservation, analytical equation was build to calculate the transient head of a mixed pump. From the theoretical analysis, the transient head was composed of a steady term and an unsteady term which was determined by angular acceleration and flow rate acceleration. The equation showed that an angular acceleration term would increase the total head for positive angular accelerations while flow rate acceleration would decrease the total head for positive flow rate accelerations. The theoretical transient head was calculated and compared to the numerical head. They were in good agreement. Factors affected the computational accuracy of the theoretical transient head were analyzed and improvements were proposed. Transient head was also compared with quasi-steady head. At the beginning of the starting period, an angular acceleration term contributed most of the total head. With time went on (t=0.5s-1.0s), with the great increase of flow rate, the total head was significantly smaller than the steady head in the same rotate speed and flow rate. The result showed that in mild transient conditions the quasi-steady head could be used to replace the transient head.