Methodology of selecting a molecular substantiated optimal cubic equation of state

Abstract

Abstract The results related to the possibility of choosing the optimal cubic equations of state (ES) are presented. The study is carried out in the framework of a new model among three-term ES based on the molecular model of interacting point centers (IPC) and the well-known two-term ES of the van der Waals type. Manifestations of acting between molecules-points of attraction and repulsion forces are reflected in the structure and parameters of the ES belonging to the basic one-parameter family. The selection technique presented earlier was based on the possibility to obtain a consistent set of parameters that form the optimal equation. As a generalization of the limit variants of the ES with various manifestations of forces, a simple three-term four-parameter ES is proposed and investigated. All parameters make sense. Two relative parameters form the equation. It is shown that the known ES of Ishikawa, Chang, and Lu after the transformation become a special case of the ES of the IPC and cannot be considered as a general one. The technique was tested by calculating the critical isotherms of a number of substances, including argon, isopentane, carbon dioxide, etc. The next step should be to connect to the analysis a more finely structured control parameter.