A PERTURBED HARD-SPHERE CHAIN EQUATION OF STATE FOR APPLICATIONS TO HYDROFLUOROCARBONS, HYDROCARBONS AND THEIR MIXTURES

The evaluation of thermodynamic properties of pure hydrofluorocarbons and hydrocarbons, and their binary mixtures is considered. A modificat ion of the perturbed-hard-sphere-chain equation of state is applied to these compounds and tested on a large database of refrigerants, hydro carbons and their mixtures, with reference to both volumetric and equi librium properties. The ability of the proposed model to reproduce exp erimental values is discussed. First, the theoretical background of th e model is revisited in order to obtain a predictive method for the 'a priori' calculation of the values of parameters which reflect the siz e, shape and interaction energy of the molecule (three parameters for each pure component). Expressions to predict these values as a functio n of molecular quantities are presented and it is shown that the propo sed model can be reliably used for calculating the properties of pure refrigerants and hydrocarbons, starting from the Bondi volume and surf ace area values, and the vapor pressure curve (2% error in the PVT beh avior at worst). Then, the extension to mixtures is addressed. Attenti on is focused on the evaluation of binary interaction parameters (k(ij )) for systems of refrigerant-refrigerant, hydrocarbon-refrigerant and hydrocarbon-hydrocarbon type. Vapor-liquid equilibrium data of eighte en binary systems at several temperatures have been regressed, with er rors in pressure ranging below 2% for refrigerant and below 1% for hyd rocarbons when using a single value of k(ij) for each binary pair, ind ependent of temperature. (C) 1998 Elsevier Science Ltd. All rights res erved.