A combined density gradient theory with equation of state model for the study of surface tension of refrigerant fluids

Abstract

A combined density gradient theory (DGT) with an equation of state (EoS) model has been employed for describing the surface tension of 26 pure refrigerant fluids. Two EoSs were considered to be employed in the model development. The first one is the Carnahan–Starling hard-sphere equation with the perturbation term of Dohm-Prausnitz (CS-DP EoS) and the second one is the modified version of that EoS, i.e., MCS-DP. Then two different DGT-based models (DGT + CS-DP and DGT + MCS-DP) were employed for calculating the surface tension of pure refrigerants. The surface tension data source was provided from NIST databank and several original papers, as well. Both DGT models used one unique value for the influence parameter for each fluid. The DGT + MCS-DP model with the average absolute deviations (AADs) of 4.23% was found to be almost as accurate as DGT + CS-DP model with AAD of 4.84% for the correlation of NIST data. But in case the calculation of experimental surface tensions, DGT + CS-DP and DGT + MCS-DP models led to AADs of 5.88% and 3.74%, respectively, which reveals very well the superiority of DGT + MCS-DP against DGT + CS-DP one. All calculations on the surface tension of studied refrigerants were carried out in 0.45–0.95 of reduced temperature. Then, the degree of accuracy of DGT + MCS-DP model has also been compared with some simple empirical equation based on the corresponding states principle.