Effect of Binary Interaction Parameter on Surface Tension of Binary Refrigerant Fluids: Linear Gradient Theory

Abstract

Surface tension (ST), as a thermophysical property, has many applications in industry. Linear gradient theory (GT) is widely used to predict ST. Based on GT and the equation of state of cubic plus association (CPA), a method for calculating the ST of refrigerant mixtures is proposed in this work. Also, a new relationship has been considered for the influence parameter (IP), which is a function of the bulk and vapor phase densities, and it has a variable exponent \(n\). At first, the unknown coefficients (\(A\) and \(B\)) of the IP were calculated for pure refrigerants, then the binary interaction parameter \(\left( {{{l}_{{ij}}}} \right)\) was calculated for binary refrigerant mixtures to optimize the proposed model. Finally, the ST of eight binary refrigerants was obtained for different concentrations, and the calculations were repeated for five different powers of the IP. In our calculations, we considered both zero and nonzero binary interaction parameters. The results from this model show that the calculated ST is in good agreement with the experimental values. The best result is related to the binary R32+R134a considering the power of –2.5 in the proposed equation of the IP and proposing the nonzero binary interaction parameter (AAD ~ 1%)