A comparison of homogenous and separated flow assumptions for adiabatic capillary flow

Homogenous and separated flow models are investigated for use in modeling one-dimensional adiabatic capillary tube flow. While these methods have been utilized extensively within the literature, the current work provides a rigorous, quantitative comparison of their accuracy using recent experimental data. Simulations utilizing the working fluids R134a, R600a, and R744 are performed for both methods and validated against experimental data. The mean error of the homogenous flow method is 8.55%, 5.4%, and 8.13%, respectively for R134a, R600a, and R744. The mean error of the separated flow method is 5.77%, 4.57%, and 8.03%, respectively for R134a, R600a, and R744. The separated flow method was found to have a smaller mean error and to perform better than the homogenous method as determined by non-parametric statistical tests.

► A homogeneous and a separated flow model are applied to capillary flows.
► A density-based discretization is used for the homogeneous model.
► The models are validated for different refrigerants, capillary geometries.
► The error shows clear non-normal tendencies and bias.
► Non-parametric statistical tests confirm the benefits of the separated flow model.