A perturbed hard sphere chain equation of state for applications to hydrofluorocarbons, hydrocarbons and their mixtures

Abstract

The evaluation of thermodynamic properties of pure hydrofluorocarbons and hydrocarbons, and their binary mixtures is considered. A modification of the perturbed-hard-sphere-chain equation of state is applied to these compounds and tested on a large database of refrigerants, hydrocarbons and their mixtures, with reference to both volumetric and equilibrium properties. The ability of the proposed model to reproduce experimental values is discussed. First, the theoretical background of the model is revisited in order to obtain a predictive method for the ‘a priori’ calculation of the values of parameters which reflect the size, shape and interaction energy of the molecule (three parameters for each pure component). Expressions to predict these values as a function of molecular quantities are presented and it is shown that the proposed model can be reliably used for calculating the properties of pure refrigerants and hydrocarbons,starting from the Bondi volume and surface area values, and the vapor pressure curve (2% errorin the PVT behavior at worst). Then, the extension to mixtures is addressed. Attention is focusedon the evaluation of binary interaction parameters ( k ij ) for systems of refrigerant–refrigerant, hydrocarbon–refrigerant and hydrocarbon–hydrocarbon type. Vapor–liquid equilibrium data of eighteen binary systems at several temperatures have been regressed, with errors in pressure ranging below 2% for refrigerant and below 1% for hydrocarbons when using a single value of k ij for each binary pair, independent of temperature.