CFD simulation of scroll expanders: Influence of pressure ratio and flank clearance over the performance

Abstract

© ECOS 2019 - Proceedings of the 32nd International Conference on Efficiency, Cost, Optimization, Simulation and Environmental Impact of Energy Systems. All rights reserved.Scroll expanders are considered ideal for low power applications, in particular in small scale ORC (organic Rankine cycle). Internal leakages decrease considerably the isentropic efficiency of scroll expanders and consist the main source of inefficiency. In this paper, the performance of one scroll expander working with air for which experimental data is available is simulated. The influence of pressure ratio and tangential clearance over the results is investigated. Transient 2D CFD (computational fluid dynamics) simulations of the compressible flow capable of quantifying the internal leakages present in this machine were performed. The filling factor, generated power and isentropic efficiency were obtained and compared with experimental results from our research group. The results obtained reveal that the pressure ratio variation does not change the filling factor, thereby the internal leakages remain practically constants with the inlet pressure increase. The pressure ratio value for which the highest isentropic efficiency is obtained tends to reduce when increasing the internal leakages. The CFD simulations have shown generated power 11% higher if compared with experimental results. This difference can be attributed to uncertainty in tangential clearance measurements, radial leakage and pressure drop at expander inlet not considered in the 2D simulations.