GENERALIZED QUARTIC EQUATION OF STATE FOR PURE NONPOLAR FLUIDS

A generalized quartic equation of state has been developed for pure no npolar fluids. The equation of state contains four parameters which de pend on three properties of the fluid-critical temperature, critical v olume, and acentric factor. A mathematical approximation based on prev iously reported hard-sphere molecular dynamics simulations has been us ed to model repulsive contributions to the pressure. Attractive forces were modeled using an empirical term. While the quartic equation yiel ds four roots, one root is always negative and hence physically meanin gless, and three roots behave like three roots of a cubic equation. Th us, the new equation of state has the advantages of a cubic, simplicit y and unequivocal identification of the roots, while correctly modelin g the attractive and repulsive contributions to the pressure. The new equation of state is more accurate than either the Peng-Robinson or a previously proposed quartic equation of state. Accuracy in the supercr itical and compressed liquid regions is improved substantially.