A three-parameter corresponding states model for non-polar fluids based on multiparameter reference equations of state

In this work a three-parameter corresponding states model is presented. In this model residual thermodynamic properties are calculated by linear interpolation between those of two reference fluids, i.e. methane and carbon dioxide. The properties of these two fluids are obtained from the corresponding multiparameter reference equations of state: the Setzmann and Wagner equation for methane and the Span and Wagner equation for carbon dioxide. By this device, the model retains the basic structure and ease-of-use which is proper of analogous models, the Lee-Kesler model for instance, but the accuracy of the model is greatly improved as is demonstrated in this work by comparison with the Lee-Kesler model and a recent generalised corresponding states model by Sun and Ely. Also, the proposed model showed to be far more accurate than the Peng-Robinson equation of state. The percentage average absolute deviations were: 0.529 in pρT data, 0.814 in vapour pressures, 0.553 in saturated-liquid densities, 1.398 in saturated-vapour densities, 1.787 in isochoric heat capacities, 1.576 in isobaric heat capacities and 0.829 in speeds of sound. These results were obtained for a set of 19 non-polar and slightly polar fluids comprising: methane, ethane, propane, isobutane, n-butane, n-pentane, n-hexane, n-heptane, n-octane, ethylene, cyclohexane, benzene, toluene, nitrogen, carbon dioxide, carbon monoxide, hydrogen, oxygen and argon.