Predictions of thermodynamic properties of pure fluids, refrigerants, and binary mixtures using modified Peng-Robinson equation of state

The Peng-Robinson (PR) EOS is a very successful two-parameter equation of state to estimate thermodynamic properties of pure compounds as well as mixtures. The PR EOS has been modified and revised several ways to improve estimates, and the most popular modification is for the attractive term through alpha function and temperature dependent covolume parameter in the repulsive term. However, the unphysical, i.e., negative values of temperature dependent co volume parameter at high temperature lead to undesirable results. We have addressed this issue in the present work by incorporating a temperature dependent covolume parameter and yet physically consistent over a large range of temperature. In the present work, the Modified-Peng-Robinson 2 (MPR2) equation of state is presented by modifying the alpha function in attractive term and temperature dependent co-volume parameter in repulsive term of the PR EOS. The accuracy of MPR2 EOS is demonstrated by comparing results with the PR, HKM1, and MPR1 equations of state. The thermodynamic properties, namely saturated vapor pressure and liquid density, enthalpy of vaporization, compressed liquid densities in sub and supercritical region, heat capacities (isobaric and isochoric), and sound velocity of pure compounds, are predicted by MPR2 EOS which agrees very well with the experimental data. We have further studied 24 refrigerant properties like vapor and liquid densities. The work has also been extended to study the phase behavior of 26 binary mixtures using van der Waals single fluid mixing rules.