Mass flow rate of non-equilibrium subcooled two-phase flow of R600a in a household refrigerator-freezer

Abstract

A few researchers recently reported the presence of vapor bubbles of R600a at the inlet of the capillary tube of refrigerators under subcooled conditions. However, the effect of a non-equilibrium two-phase state on the refrigerant mass flow rate has not yet been addressed. The aim of this study was firstly to investigate the effects of ambient temperature and R600a charge amount on the refrigerant state at the inlet of the capillary tubes and, secondly, to examine the ability of empirical correlations for prediction of the refrigerant mass flow rate under a non-equilibrium two-phase state. A transparent tube was installed at the inlet of the capillary tubes of a parallel two-circuit cycle refrigerator-freezer for visualization of the refrigerant flow. The visualization results demonstrated the presence of a non-equilibrium state under subcooled conditions. The experimental mass flow rates were compared with predictions by empirical correlations of Rasti et al. and Wolf and Pate. Both correlations predicted the mass flow rate with a large deviation under a non-equilibrium state and acceptable deviation under a fully liquid state. Results showed that the mass flow rate under a non-equilibrium two-phase state significantly decreased compared to the fully liquid condition. Finally, a new empirical parameter was introduced to consider the non-equilibrium two-phase flow. The new parameter was applied to previous empirical correlations and the modified version of Rasti et al.’s correlation showed good agreement with the experimental data under a non-equilibrium two-phase state.