EQUATION OF STATE CALCULATIONS AND MONTE-CARLO SIMULATIONS OF INTERNAL ENERGIES, COMPRESSIBILITY FACTORS AND VAPOR-LIQUID-EQUILIBRIA FOR LENNARD-JONES FLUID MIXTURES

Internal energies, compressibility factors and vapor-liquid equilibria for Lennard-Jones fluid mixtures are simulated by using Monte Carlo techniques, where the potential parameters epsilon12 and sigma12 between the different kinds of molecules are much different from the Lorentz-Bertherot rule. These simulations results are used to test the accuracy of the equations of state for the Lennard-Jones fluid mixtures. An accurate equation of state for the Lennard-Jones pure fluid is extended to mixtures by using four different mixing rules; a van der Waals one-fluid model, a modified van der Waals one-fluid model, a mean density approximation and a mixing rule based on the idea of Putting the Advantage of Perturbation theories to Practical Use in a simple form (PAPPU). The Weeks-Chandler-Andersen (WCA) perturbation theory is also tested. Comparison with the computer simulation results shows that the equation of state extended to mixture via the PAPPU mixing rule gives the best results. For mixtures with sigma12 different from the value given by Lorentz-Bertherot rule, the WCA perturbation theory and the equations of state extended to mixtures via these mixing rules give poor results in general.