Study of efficiency of a multistage centrifugal pump used in engine waste heat recovery application

A test bench of a multistage centrifugal pump was constructed using R123 as working fluid in simulative organic Rankine cycle (ORC) conditions. Experimental results of the pump under various operating conditions were obtained based on controlled working frequency and mass flow rate. The effect of the key pump parameters on the ORC performance was analyzed in this study. In addition, the control strategy of the pump was presented. Results show that the overall pump efficiency was between 15% and 65.7%. The outlet pressure, pump efficiency, and ORC thermal efficiency increased with the working frequency of the pump. The mass flow rate needed to be regulated as the frequency became increasingly high. The maximum thermal efficiencies of the ORC system corresponding to various working frequencies of the pump were observed. Furthermore, back work ratio (BWR) can reach up to 0.45 with the increase of the evaporating temperature of the ORC system. Pumping power should not be neglected for small-scale ORC applications, and pump efficiency assumptions should be dependent on experiments. Low pump efficiency affected the increase of the thermal efficiency and net power of the ORC system. The superheat degree was also discussed.