Numerical investigations of a Trilateral Flash Cycle under system off-design operating conditions

The current research presents a comprehensive model of a 100 kWe Trilateral Flash Cycle TFC system composed of sub-modules for the plate heat exchangers and twin-screw expanders to assess and identify the operating parameters that mostly affect the TFC performance at off-design conditions. The modelling approach for heat exchangers and piping is based on 1D CFD while considering the operating maps for pump and expander. The simulation process takes into account variations of the heat source temperature and mass flow rate from the design point. The TFC performance is analysed in terms of efficiency and power output while the expander performance is discussed in terms of volumetric and isentropic efficiencies. A sensitivity analysis is carried out to assess the most suitable parameter for control purposes and system performance optimisation. The results point out a large sensitivity of the inlet quality at the expander due to the revolution speed of the machine but also the off-design behaviour of the heater.