Dynamic modelling and sensitivity analysis of parameters impacting the performances of a liquid piston-based energy conversion system

The present work deals with the dynamic modelling of a small-scale thermo-hydraulic engine, designed for residential application. Comparing to Organic Rankine systems, the CAPILI cycle uses a hydraulic motor instead of a turbine. The solar activated CAPILI engine produces electricity through a liquid piston oscillating between two reservoirs connected alternatively to a high pressure evaporator and a low pressure condenser. The heat rejected by the condenser is discharged in the ground through geothermal probes at 13 °C while the solar panels provide heat at about 70 °C. The liquid piston drives a hydraulic motor coupled to an electrical generator to produce electricity. Based on these temperature conditions, the dynamic modelling approach undertaken in the study enables a sensitivity analysis of the most impacting parameters of the CAPILI system. In particular, the study focuses on the volume capacity and the filling ratio of transfer cylinders, the switching -balancing- volume of the cycle as well as the electrical load. The results highlight the effects of each investigated parameters on the whole behaviour of the simulated CAPILI system. The best performance of the investigated CAPILI system operating under the given operating conditions, highlights a thermal efficiency of 9.14 % and almost 55 % for the exergy efficiency.