CFD analysis of the flashing flow characteristics of subcritical refrigerant R134a through converging-diverging nozzles

Abstract A CFD-based numerical analysis of the choking flashing flow characteristics in R134a converging-diverging nozzles is presented in this paper. The CFD results are validated with available experimental data of R134a converging-diverging nozzles. After that, the critical mass flux and effects of geometric dimensions on the performance of converging-diverging nozzles are investigated. Furthermore, the calculated critical mass fluxes are compared to that of the classical models. Results show that the metastable state in R134a converging-diverging nozzle is weaker than that of water at the same operating parameters and a higher choking correction factor of R134a compared to that of water is obtained. The optimum ratio of nozzle exit diameter to the throat diameter of 2.4 is recommended among the studied nozzle geometry dimensions. Effect of the divergent length on the nozzle flow characteristics is relatively smaller than that of the nozzle exit diameter.