Equations of State for Technical Applications. I. Simultaneously Optimized Functional Forms for Nonpolar and Polar Fluids

New functional forms for multiparameter equations of state have been developed for non- and weakly polar fluids and for polar fluids. The resulting functional forms, which were established with an optimization algorithm which considers data sets for different fluids simultaneously, are suitable as a basis for equations of state for a broad variety of fluids. With regard to the achieved accuracy, the functional forms were designed to fulfill typical demands of advanced technical application. They are numerically very stable, and their substance-specific coefficients can easily be fitted to restricted data sets. In this way, a fast extension of the group of fluids for which accurate empirical equations of state are available becomes possible. This article deals with characteristic features of the new class of simultaneously optimized equations of state. Shortcomings of existing multiparameter equations of state widely used in technical applications are briefly discussed, and demands on the new class of equations of state are formulated. Substance specific parameters and detailed comparisons are given in subsequent articles for the non- and weakly polar fluids (methane, ethane, propane, isobutane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, argon, oxygen, nitrogen, ethylene, cyclohexane, and sulfur hexafluoride) and for the polar fluids (trichlorofluoromethane (CFC-11), dichlorodifluoromethane (CFC-12), chlorodifluoromethane (HCFC-22), difluoromethane (HFC-32), 1,1,2-trichlorotrifluoroethane (CFC-113), 2,2- dichloro-1,1,1-trifluoroethane (HCFC-123), pentafluoroethane (HFC-125),