Experimental performance evaluation of a multi-diaphragm pump of a micro-ORC system

The performance of micro-scale ORC systems strongly depends on the performance of their key components. While the heat exchangers and expander have been extensively investigated, the pump has only received limited attention. The main purpose of this work is the experimental characterization of a multi-diaphragm positive displacement pump, integrated in an experimental ORC system with a rated power output of 4kWel. The study focuses on the experimental evaluation of the pump performance and on cavitation phenomena. A detailed presentation of the experimental procedure and results is supplied. A great effort has been spent in calculating the global and volumetric pump efficiencies for a wide range of operational conditions, which reach maximum values around 45-48% and 95%, respectively. With regards to cavitation issues, the effect of the available Net Positive Suction Head at the pump inlet has been deeply investigated both at partial and full load to obtain guidelines for stable operation. Finally, an extensive dataset of steady-state operating points has been used to calibrate an improved version of a semi-empirical model previously developed for positive displacement ORC pumps. Special attention has been given to the ability of the model to accurately predict the behaviour and performance of the pump at different, properly chosen, steady-state conditions. Relative errors in between 0.5%, for the outlet temperature, and 10%, for the electric power consumption, are achieved.