EXPERIMENTAL INVESTIGATION OF CENTRIFUGAL PUMP REGULAR AND REVERSE MODE

Pumps as turbines have been successfully applied in a wide range of small hydro sites in the world. Since the overall efficiency of these machines is lower than the overall efficiency of conventional turbines, their application in larger hydro sites is not economical. Therefore, the efficiency improvement of reverse pumps is essential. In this study, by focusing on a pump impeller, the shape of blades was redesigned to reach a higher efficiency in turbine mode. After each modification, a new impeller was tested in the test rig. The efficiency was improved in all measured points by the optimal design of the blade and additional modification as the rounding of the blade’s profile in the impeller inlet and hub/shroud inlet edges in turbine mode. Experimental results confirmed the numerical efficiency improvement in all measured points. This study illustrated that the efficiency of the pump in reverse operation can be improved just by impeller modification the effects of impeller rounding on a combination of radial flow and mixed flow pumps as turbines using experimental data. The impeller rounding is seen to have positive impact on the overall efficiency in different operating regions with an improvement in the range of 1–3%. The behavior of the two control variables have been elaborately studied in which it is found that the system loss coefficient has reduced drastically due to rounding effects, while the extent of changes to the exit relative flow direction seems to be limited in comparison. The larger picture of impeller rounding has been discussed in comparison with performance prediction models in pumps as turbines. The impeller rounding technique is very important for performance optimization and recommends its application on all pump as turbine projects.