Linear gradient theory for modeling investigation on the surface tension of (CH4+H2O), (N2+H2O) and (CH4+N2)+H2O systems

• Linear gradient theory model for surface tension of (CH4 + N2) + H2O system.
• Using influence parameter as a function of densities of the bulk phases.
• Constant binary interaction parameter for the mixture influence parameter.

The aim of this work is to model the surface tension for (CH4 + H2O), (N2 + H2O) and (CH4 + N2) + H2O systems. The linear gradient theory (LGT) in combination with the cubic-plus-association equation of state (CPA EOS) has been applied for modeling the surface tension of (CH4 + H2O), (N2 + H2O) and (CH4 + N2) + H2O systems. The influence parameter in terms of the liquid and vapor densities has been applied. The geometric mixing rule has been also used for the influence parameter of the mixtures. First, the influence parameters of pure components have been determined. Then, the binary interaction coefficients for the influence parameters of (CH4 + H2O) and (N2 + H2O) systems have been correlated. The influence parameters of pure components and binary interaction coefficients have been applied for (CH4 + N2) + H2O system. The calculated surface tension values have a good agreement with experimental data for (CH4 + N2) + H2O system (overall AAD ∼ 3.42).