Extension of Tao-Mason Equation of State to Mixtures: Results for PVTx Properties of Refrigerants Fluid Mixtures

Tao and Mason (J. Chem. Phys. 1994, 100, 9075-9084) developed a statistical-mechanical-based equation of state (EOS) for pure substances. In the present study, we have successfully extended this EOS to fluid mixtures, selecting refrigerant fluid mixtures as the test systems. The considered refrigerant mixtures are R32 + R125, R32 + R134a, R134a + R152a, R125 + R143a, R125 + R134a, R32 + R227ea, R134a + R290, and R22 + R152a. The second virial coefficient, B(T), necessary for the mixture version of the Tao-Mason (TM) EOS, was determined using a two-parameter corresponding-states correlation obtained from the analysis of the speed of sound data and two constants: the enthalpy of vaporization Delta H-vap and the molar density rho(nb), both at the normal boiling point. Other temperature-dependent quantities, including the correction factor alpha(T) and van der Waals covolume b(T), were obtained from the Lennard-Jones (12-6) model potential. The cross parameters B-12(T), alpha(12)(T), and b(12)(T), required by the EOS for mixtures, were determined with the help of simple combining rules. The constructed mixture version of the TM EOS was extensively tested by comparison with experimental data. The results show that the molar gas and liquid densities of the refrigerant mixtures of interest can be predicted to within 1.3% and 2.69%, respectively, over the temperature range of 253-440 K and the pressure range of 0.33-158 bar. The present EOS was further assessed through comparisons with the Ihm-Song-Mason (ISM) and Peng-Robinson (PR) equations of state. In the gas phase, the TM EOS outperforms the two other equations of state. In the liquid phase, there is no noticeable difference between the TM EOS and the PR EOS, but both work better than the ISM EOS.