Investigation of flow characteristics in a single screw expander: A numerical approach

In this paper, a three-dimensional computational fluid dynamics (CFD) simulation is carried out to investigate the performance of a single screw expander by linking its behavior with the dynamic features of the flow field. To study this aspect and other phenomena that can affect expander operation in an actual Organic Rankine Cycle (ORC) system, in this work an approach based on the dynamic analysis of the machine operation with the use of both the overset mesh strategy and real gas modeling is showed. The expansion process is investigated to analyze both flow characteristics and machine performance during on-design operating conditions. The model aims to investigate the SSE operation without the effects of the sealing process of the lubricant oil to highlight the effects of the fluid expansion on the SSE operation. Pressure and flow patterns which resulted from this analysis depend on the design characteristics of the machine, operating conditions, and working fluid properties. The resulting output torque and isentropic efficiency are coherent with the simulated operating conditions.