Modeling the surface tension of refrigerant mixtures with linear gradient theory

•Combining the linear gradient theory with the Heyen EOS.•A new density dependant correlation for the influence parameter.•Using geometric mixing rule for the mixture influence parameter.•Very good agreement between predicted and experimental surface tensions.

In this work, the surface tensions of pure refrigerants and binary, ternary, and quaternary refrigerant mixtures were modeled. A simple and reliable model was used, combining the linear gradient theory (LGT) with the Heyen equation of state (Heyen EOS), to take advantage of the well described equilibrium densities of phases and surface tensions of refrigerant mixtures. The binary interaction parameters of the Heyen EOS were determined to improve the description of the equilibrium properties of bulk phases. A new correlation for the influence parameter is also proposed that is a function of the densities of the bulk phases. The geometric mixing rule for the mixture influence parameter is also selected without adjustable coefficients, making this model predictive. The surface tensions predicted by the model agree well with experimental data for pure refrigerants and binary, ternary, and quaternary refrigerant mixtures (overall AAD∼3.27%).