OPERATION OF CENTRIFUGAL PUMP AT PART LOAD CONDITIONS

The paper presents the results of experimental studies on the onset, extent and structure of the flow recirculations at both inlet and outlet of a radial pump impeller. The study was conducted a various flow rates and a rotational speed of 2500 rpm. Balances of mass, momentum and energy were determined, and the losses prevalent at part load conditions under consideration of flow recirculation’s were analyzed with the aid of the measured distributions of velocity and total pressure near impeller inlet and outlet. The results showed that the recirculating flow in the inlet and the outlet appeared for flow rate ratios Q / Q_opt ≤ 0.7 and Q / Q_opt ≤ 1, respectively. At zero flow rate the ratio of the suction recirculating flow (Q_r,s) to the optimum flow rate (Q_opt) is 0.6 approximately. Also at zero flow the discharge recirculating flow (Q_r,d) was almost twice as larger as (Q_r,s). For the test impeller the critical flow rate at which the recirculating flow occurred at outlet was larger than that at inlet. In addition, the results indicated that the transfer of moment of momentum and energy to the recirculating flow which takes place inside the impeller increased with decreasing the flow rate. Analysis of losses indicated that the energy transferred to the recirculating flows could be regarded as additional impeller losses.