Improving cubic EOSs near the critical point by a phase-space cell approximation

Cubic equations of state (EOSs) are widely used to model the thermodynamic properties of pure fluids and mixtures. However, because they fail to accou nt for the long-range fluctuations existing in a fluid near the critical po int, they do not accurately predict the fluid properties in the critical re gion. Recently, an approximate renormalization group method was developed t hat can account for these fluctuations. A similar method is applied to prov ide corrections to a generalized cubic EOS for pure fluids, which is able t o represent all classic cubic EOSs. The proposed approach requires two addi tional parameters: <(c)over bar(RG)> and Delta. The value of <(c)over bar(R G)> is correlated to experimental critical compressibility data, while Delt a is set equal to 1. The method is applied to predict the saturated liquid density of fluids of different polarity, and the corrections to the origina l EOS are found to significantly improve the predictions of this property b oth far from and close to the critical point. Finally, a correlation is pre sented for the direct evaluation of the parameter <(c)over bar(RG)> from th e value of the critical compressibility factor.