Predicting the Surface Tension of Refrigerants from Density Gradient Theory and Perturbed Hard-sphere Equation of State

The surface tensions of pure refrigerants were predicted using a density gradient theory (DGT) coupled with a perturbed hard-sphere equation of state (EoS) approach. The EoS is taken from the Carnahan-Starling hard-sphere equation with the perturbation term of Dohm- Prausnitz (CS-DP EoS), in which the relevant parameters to the molecular size and energies are universal functions of temperature in describing the equilibrium bulk properties. Then DGT+CS-DP EoS model has been employed for predicting the surface tension of 26 pure refrigerants taken from a Chemistry Webbook provided by NIST. Our calculations on the surface tension data from the DGT+CS-DP model led to an average absolute deviation of 4.84%. Then, the degree of accuracy of DGT+CS-DP model has also been compared with another DGT-based model. Nomenclature and Units AAD Average absolute relative deviation γ Surface tension (mN m-1) T Absolute temperature (K) ρ Molar density (mol m-3) y Packing fraction kB Boltzmann constant (J K-1) μ Chemical potential a(ρ) Free energy density A Helmholtz free energy P pressure (Pa) ɷ Grand free energy density c Influence parameters a1-b3 Fit coefficients to be used in characteristic functions, Fa and Fb W Acentric factor Superscripts HS Hard-sphere repulsion Exp Experimental data NIST NIST databank Calc. Calculated values Corr. Correlated values Subscripts s Saturated state