Evaluating the Performance of the PC-SAFT and CPA Equations of State on Anomalous Properties of Water

Water is the most important and at the same time the most anomalous substance on earth. Due to its importance, there are numerous studies concerned with the modeling of water using advanced equations of state (EOS) like those based on Wertheim’s perturbation theory. However, only a few of these studies deal explicitly with the performance of these models in predicting water’s anomalous properties. In this study, the performance of the perturbed chain-statistical associating fluid theory (PC-SAFT) and the cubic-plus-association (CPA) EOS on predicting several of water’s properties is investigated. Twelve PC-SAFT and two CPA parameter sets from the literature are used and compared. Despite an overall acceptable performance of both models, all parameter sets fail to satisfactorily describe second-order derivative properties and there is not a parameter set that is clearly superior. None of the two models is also clearly better than the other. Most importantly, none of the parameter sets is able to accurately predict water’s anomalous properties like the maximum of density or minimum of heat capacity with respect to temperature. These results indicate that significant improvements in the models and their underlying theories are needed for the accurate description of water’s complex thermodynamic behavior. The most promising approach is to take into consideration water’s structure.