Performance Improvement and Peculiar Behavior of Disk Friction and Leakage in Very Low Specific-Speed Pumps

Pump efficiency drops rapidly with a decrease in specific speed n_s in the very low n_s range. The cause for low efficiency of a very low specific speed pump is mainly due to large disk friction. In the present study, two methods of reducing disk friction is put forward and is confirmed experimentally. One method is to decrease the amount of leakage flow, which resulted in a rapid decrease of disk friction and raised the pump efficiency by about 7%. The other is to increase the surface roughness of impeller shroud, which raised the pump efficiency by about 3%