Evaporation in supersonic CO2 ejectors: analysis of theoretical and numerical models

Supersonic ejectors can be profitably used in supercritical CO2 vapor compression chiller to recover the throttling losses. Various configurations are possible that allow great benefits in terms of system efficiencies (COP can increase up to 30%). Although the application and testing of ejectors is not particularly difficult in these systems, the study of the internal dynamics is an extremely complex task because all phase-change phenomena inside the ejector occur at a high level of speed and compressibility. This work presents the analysis of various approaches that could be exploited to tackle the analysis of high-speed, non-equilibrium flashing of CO2 inside a supersonic ejector. The limits and advantages of some previous theoretical and numerical works are highlighted. CFD results, obtained with an in-house developed numerical model, are discussed.