Assessment of existing dimensionless correlations of refrigerant flow through adiabatic capillary tubes

As the refrigerant flow inside the capillary tubes is accompanied with phase change, non-equilibrium between two phases, and critical two-phase flow, capillary tube modeling is not as simple as its simple geometry. For the convenience of engineering applications, many investigators focused on the empirical dimensionless correlations of refrigerant flow rates through capillary tubes recently. In this paper, the dimensionless mass flow correlations of adiabatic capillary tubes in the literature are reviewed and categorized by the function forms and ways to select dimensionless parameters. Eleven dimensionless correlations are selected for further in-depth assessment on their accuracy and generality using the late experimental data from the literature. The results indicate that the model-based neural network correlations have better overall performance.