Nonlinear gradient theory and the equation of state of cubic plus association to predict surface tension of binary refrigerant fluids

In this paper, a model for predicting the surface tension (ST) of binary refrigerant fluids is proposed based on the nonlinear gradient theory (GT) and the equation of state (EOS) of cubic plus association (CPA). For this purpose, a new relationship for the influence parameter (IP) has been considered, which has a variable exponent n. It is a function of the bulk liquid phase density and vapor phase density. First, the used parameters (A and B) of the IP were calculated for pure refrigerant fluids by obtaining the ST and fitting with the experimental data. Then, the ST of four binary refrigerant fluids was calculated for five different exponents of n, and different mole fractions. The results of this model show that the calculated ST is in good agreement with the experimental values, and the best result corresponds to the exponent of [Formula: see text] in the proposed relation of the IP.