A generalized continuous empirical correlation for the refrigerant mass flow rate through adiabatic straight and helically coiled capillary tubes

In spite of the simple geometry of capillary tubes, the refrigerant flow behavior through capillary tubes is complex. Numerous empirical correlations have been developed to predict the refrigerant mass flow rate through adiabatic helically coiled capillary tubes, but all of them have discontinuity problems at the saturated liquid line. In the present study, a generalized continuous empirical correlation is developed that can be used to predict the refrigerant mass flow rate through adiabatic helically coiled capillary tubes as well as straight capillary tubes. The new correlation can accommodate both subcooled liquids and saturated two-phase flow conditions in the capillary tube inlet condition. The proposed new correlation is validated with experimental data for R-22, R-134a, R-407C, R-410A, and LPG. In addition, the new correlation was compared with previous empirical correlations available in the open literature. The present correlation showed excellent performance in terms of its application range and degrees of continuity and accuracy.