Optimization of Hydrodynamic Design for a Mixed-flow Pump and Performance Verification

Abstract

Pumps are used in various plant industries such as chemical, nuclear power plant and marine industries and they are categorized into different groups according to their required specifications. Centrifugal pump is designed when specification requires low flow-rate and high pressure while axial-flow pump would be designed if high flow-rate and low pressure is required. Specific speed is defined by flow-rate, total head and rotational speed, and pumps are classified as centrifugal type, mixed-flow type and axial-flow type according to their specific speed and operational characteristics. Specific speed is highly related to pump shapes which have certain tendencies depending on the specific speed. In this paper, design optimization of mixed-flow pump was carried out with Design of Experiment(DOE) for selected specific speed section in order to establish data base of design optimization for mixed-flow pump according to specific speed. From design variables of impeller and diffuser of mixed-flow pump, major design variables that affect pump performance were analyzed and selected through 2k factorial designs. Impeller and diffuser shapes that satisfy design specification of mixed-flow pump under certain specific speed were generated by conducting design optimization utilizing Response Surface method(RSM) on selected major design variables. Tendencies of design variables were analyzed according to specific speed in order to build design optimization D/B(data base) of optimally designed mixed-flow pump under certain specific speed. Tendencies of design variables from impeller and diffuser depending on specific speed show tendencies of certain curves. Therefore, impeller and diffuser shapes of mixed-flow pump can be designed if tendencies of design variables from impeller and diffuser depending on specific speed are secured. Impeller and diffuser shapes of Ns475 mixed-flow pump were generated by using tendencies of design variables that were established through design optimization D/B of mixed-flow pump. Performance verification of numerical analysis and performance experiment was carried out on designed mixed-flow pump shape, and the reliability of the designed pump shape was secured by comparative verification process on the experiment results. Ns475 mixed-flow pump was proven to satisfy required design specification and pump performance as it was designed by using D/B of design optimization. Numerical analysis was conducted with the mixed-flow pump on impeller and diffuser including blade section in order to analyze Ns475 mixed-flow pump. The shapes such as inlet part bell mouth, hub cap, and tip clearance were materialized from actual shape of mixed-flow pump, and changes of pump performance according to shapes were analyzed. Performance experiment of Ns475 mixed-flow pump was carried out using devices manufactured in accordance with ISO 5198 standard. In order to secure reliability of measurement result, measuring sensor that had been maintained with regular calibration was used. KS B 6301 : 2015 standard was applied for experiment condition and method of pump performance experiment in carrying out the experiment and analyzing pump performance. The reliability of impeller and diffuser shapes of Ns475 mixed-flow pump generated using design optimization D/B were secured through objective analysis of pump performance using the results of numerical analysis and experiment.