In order to increase pump efficiency and apply an optimum design method of a low specific speed centrifugal pump less than 127 [m, m3/s, min-1], twelve kinds of volute casing with the same impeller are designed at impeller blade outlet angle of 34 degree. With each volute tongue shape, there is one volute casing, respectively. The effect of these volute casing shapes is investigated by using computational fluid dynamics (CFD). In this present study the optimum design method in combination of volute tongue shape operating variables for pump performance enhancement is analyzed. Based on design of experiments (DOE) technique, the required experiment trials are determined. The optimization results are pointed out. The parameters chosen for optimum design are the volute tongue angle and the gap between impeller and tongue. The levels for the parametric specification are chosen in the ranges where the pump gets the best efficiency. The results demonstrate that the conventional design is not suitable for a low specific speed. After optimizing the volute tongue, the pump achieves the best performance at 0o of the volute tongue angle with the appropriate gap between impeller and volute tongue. It is observed that pump efficiency was improved up to 75.01%.
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