Perturbation equation of state of pure fluids

The statistical thermodynamic perturbation equation of state, originally developed for fluids with Lennard-Jones intermolecular potential energy is improved, and then it is modified for the prediction of real fluid properties. The improved equation of state, when applied to Lennard-Jones fluid, predicts the properties of this fluid consistently better than the original perturbation equation of state.In order to modify the perturbation equation of state for the prediction of real fluid propertes both pair-, and triplet-interaction potential functions are considered in the formulation of this equation of state. For the pair-interaction potential function the Kihara spherical-core function is used, and for the triplet-interaction potential function the Axilord-Teller function is used. Comparisions are made between the calculated and the experimental thermodynamic properties of argon, methane and neopentane in liquid and in vapor states. These comparisions indicate that the perturbation equation of state is very promising in predicting the properties of real fluids in condensed states.