STUDY ON HIGH EFFICIENCY AND HIGHLY RELIABLE DESIGN OF SMALL SIZED PUMP WITH LOW SPECIFIC SPEED

摘要

In order to suppress the pump efficiency deterioration as lower as possible, the small-sized pump with low specific speed, in which the impeller outlet velocity was larger than that of regular pumps, was designed by a simple optimum design method combined with blade surface singularity method for decreasing the total loss generated at impeller outlet and in volute casing. Several combinations of centrifugal impeller and volute casing were manufactured and tested for confirming the availability of this design method. And numerical simulation by vortex method was also conducted to reconfirm internal flow. The computational and experimental results, for small sized pump with low specific speed, show as follows: Strong reverse flow is easily formed in the blade-to-blade of impeller, which is calculated by both singularity method and vortex method. The semi-open impeller with blade outlet angle of thirty-five degrees, designed by the optimum design method, yielded the highest efficiency of sixty-one percents among test impellers in the case of narrow tip clearance. In the case of larger tip clearance, however, the leakage loss becomes dominant for pump efficiency and the efficiency of impeller with blade outlet angle of sixty degrees is higher. This fact implies that the tip clearance should be considered as an additional factor for optimum design.