Effect of impeller inlet condition on non-overload performance of serial-parallel centrifugal pump

Abstract: Aiming at influences of different inlet flow on non-overload performance of Serial-Parallel Centrifugal Pump (SPCP), establishment of accurate prediction methods is necessary. In fact, the motor of the pump can easily burn out when the pump is working with a large flowing capacity and a high head. A pump is deemed as one with non-overload characteristics when its motor power is larger than 120% of the max shaft power, therefore the non-overloaded characteristic analysis of the SPCP plays a significant role for the safe running of the pump. In this paper, the average angle of inlet velocity (), which the impeller inlet flow distribution can be efficiently assessed, is firstly introduced to calculate the maximum shaft power (Pmax) of Single-Stage Model Pump (SSMP) in the case of impeller inlet about no-pressure straight pipe, and relevant flow () formula based on velocity triangle theory. Then, having researched the applications of SPCP in the case of two different impeller inlets: No-pressurehalf spiral and pressurehalf spiral. Once more, Computational Fluid Dynamics (CFD) is used to simulate the external characteristic curve of each model, and the enclosed experiment settings are adopted to firstly conduct analysis on the single stage model pump and then on SPCP after modifying the inlet and outlet pipes. In conclusion, analysis indicates that the results of calculation and experiments coincide with each other well. Under the design condition, the head error and the power error are respectively 1.20% and 2.40%, and when the SPCP is in the serial working condition, the head error and the power error are respectively 3.80% and 4.10%; in parallel working condition, the head error and the power error are respectively 2.90% and 3.50%. Therefore, those head errors and power errors are less than 5%, which proves the correctness of numerical simulation. What's more, with the different inlet flow state, axial velocity is distributed uniformly with a little change while the value of γ, the angle between the speed vector of unit nodes and the axial-surface streamline, has a big change. By comparing the values of the γ in different working conditions, it can be found that the non-uniform flow in serial working status is more obvious than that in parallel working status. In addition, a.k.a. , by putting these results into formulas, the theoretical and Pmax values can be obtained, which are later compared with the experimental results. The and Pmax values in non-overloaded working condition have much smaller errors when compared with experiment results, which are respectively 1.38% and 0.47% in the SSMP. However, when the SPCP is in serial working condition, it is easy to go overload. When =78.10 m3/h, the pump is at its max power point; in parallel working condition, with =168.50 m3/h, the pump is at its max power point, since the volume of flow is double that of before, for single-stage single-suction centrifugal pumps, it has its max power point only when =84.25 m3/h. In actuality, when the rated power of a SPCP motor reaches, e.g. 56.64 kW, the pump can achieve its non-overloaded characteristics. This research shows an excellent theoretical innovation, holds a high perspective and provides theoretical reference for designing the hydraulic property of SPCP.