Numerical Modeling of Refrigerants Flowing through Short Tube Orifices

A numerical model is developed for predicting the mass flow rates of a refrigerant flowing through short tube orifices under various working conditions. The numerical model is theoretically based and not refrigerant-oriented though the majority of past works are based on semi-empirical correlations. The metastable state flow is considered in the numerical model, and the critical flow condition at the outlet is directly obtained by using the analytical two-phase critical model. The comparison between the predicted mass flow rates and the experiment data obtained from literatures shows that the mean absolute deviations (MADs) for R-410A, R-407C, and R-134a are 6.91%, 5.33%, and 7.09%, respectively. The accuracy of this numerical model provides the basis for a more detailed and theoretical analyses of refrigerant flowing characteristics in short tube orifices, such as the determination of flow regimes and variation of inception of vaporization. Also, the effects of working conditions such as upstream pressure and inlet subcooling degree on the mass flow rates are theoretically studied using the developed numerical modeling technique, which shows exact trends as experiment data.