Numerical study on the effect of superheat on the steam ejector internal flow and entropy generation for MED-TVC desalination system

Abstract

The droplets formed by wet steam spontaneously condensation deteriorated the steam ejector performance for the Multi-Effect Distillation-Thermal Vapor Compression (MED-TVC) seawater desalination system. According to our numerical research, it was found that increasing the wet steam superheat was an effective method to suppress the steam spontaneously condensation behavior, especially when the superheat was increased by 50 K, the entrainment ratio was improved by 10.3% and the total entropy production was reduced by 9.8% for the steam ejector of MED-TVC system. In this paper, a wet steam model with entropy generation rate was built, the numerical simulation results of dry steam and wet steam models were compared, and the influence of five primary fluid superheat ranging from 10 K to 50 K on the wet steam flow behavior were also investigated. The irreversible analysis of wet steam flow revealed that the entropy generation was mainly concentrated in the initial mixing position of primary and secondary fluids near nozzle outlet and shock wave position in the diffuser, and the entropy generation relevant for the heat transport mechanism accounted for a much higher proportion (63%) of total entropy production than viscous dissipation (33%), phase change (4%), and wall boundary layer (ignored).