Extended corresponding states model for fluids and fluid mixtures: I. Shape factor model for pure fluids

We present a new and accurate extended corresponded states model for the prediction of thermodynamic properties of pure fluids. This model is based on shape factors expressed as functions of the reduced temperature and density, the acentric factor and the critical compression factor. Substance-dependent coefficients were optimised against volumetric, VLE and acoustic data for the light hydrocarbons from ethane to n-pentane, ethylene, nitrogen, carbon dioxide, oxygen, argon and carbon monoxide. With this model, fluid properties are estimated largely within their experimental uncertainty. The model was tested for reduced temperatures T_r in the interval 0.52≤T_r≤3.33 and for reduced densities up to 2.8. The work reported here is a necessary precursor to the development of an extended corresponding states (ECS) equation of state for natural gas systems and mixtures of natural gas constituents.