LAUSR

Abstract The efficiency of an Organic Rankine Cycle (ORC) system is heavily influenced by the expander performance. Low to medium size (between 1 and 500 kW) ORC systems are usually equipped with volumetric expanders which are often modified positive displacement compressors operated in reverse mode. In order to increase the ORC performance, in-depth analyses of the expander behavior are essential. In this paper, a 3D computational fluid dynamics (CFD) simulation is carried out to investigate the performance of a single screw expander. This machine, originally conceived as a compressor, is characterized by a central grooved rotor that engages with two satellites responsible for the sealing the working chambers. The analysis deals with the dynamic simulation of the single screw expander operation with the use of the overset mesh strategy. The simulation shows how such machine performs when installed in an ORC system. Specifically, the mass flow rate and pressure pulsations at the ports are analyzed, and both the expansion process and leakage flows are investigated. The results aim at describing the single screw operation in terms of integral performance quantities as well as flow fields in relation to the design characteristics of the machine.