Optimising prediction model of centrifugal pump as turbine with viscosity effects

Abstract

Performance conversion of a centrifugal pump as turbine from the known performance curves in pump mode is vital important in pump selection, power generation and investment assessment, especially under low Reynolds number operation conditions. Effects of Reynolds number on such a performance conversion have not been taken into account so far. In the paper, flow rate, head and output power and hydraulic efficiency conversion factors at zero efficiency/power, 0.8 part-load, best efficiency, 1.2 over-load and maximum flow rate points are defined and extracted from the performance curves of a centrifugal pump as turbine at five viscosities obtained by using CFD simulations. The conversion factors are correlated to impeller Reynolds number and a performance conversion model is proposed by employing 3rd and 4th order polynomials for the output power and head curves. New correlations of flow rate, head and efficiency conversion factors are also attempted in terms of specific speed and efficiency as well as impeller Reynolds number based on the data found in literature. The conversion model is a framework and can be useful for design of pump as turbine and its performance prediction, especially under variable liquid viscosity conditions.