Semi-empirical model of a multi-diaphragm pump in an Organic Rankine Cycle (ORC) experimental unit

Abstract Organic Rankine Cycle (ORC) power systems represent an effective option to exploit low grade heat fluxes. Several papers have been published on ORCs systems, most of them dealing with the maximization of overall system performance and selection of the working fluid. Recently, the attention has moved also to system components with specific focus on the expander. Less attention was paid to the pump which, however, may contribute significantly to the system consumption, especially in small size systems. This paper presents a semi-empirical thermodynamic model of a displacement pump integrated into an ORC experimental unit. The pump behavior at design and off-design conditions is modeled as a set of thermodynamic processes the main geometrical parameters of which are calibrated using experimental data. Calibration is performed by setting an optimization procedure which minimizes the error between operation parameters calculated by the model and measured in the test rig. Maximum errors were in the range 0.06%–7%. Differently from the few papers on similar models in the literature, this model takes into account the trapped mass flow rate, and is used to calculate the pump characteristic curves and identify incipient cavitation. A good agreement with experimental data was found in both cases.