Pressure and temperature dependencies of excess molar enthalpies of two-component Lennard–Jones fluid mixtures in the supercritical region

Monte Carlo (MC) simulations have been carried out for mixtures of Lennard–Jones (LJ) fluids near or in the supercritical region. Excess molar enthalpy at equimolar concentration, Hp,x=0.5E, has been obtained for four kinds of model mixtures each having different combining rule for unlike interactions. The pressure and temperature dependencies of Hp,x=0.5E are investigated. The unique pressure and temperature dependencies of Hp,x=0.5E for real systems such as (ethane+ethene) in the supercritical condition have been reproduced by the present simple model systems. Excess molar internal energies at constant volumes, UV,x=0.5E, are also evaluated. They are compared with Hp,x=0.5E to investigate the volumetric contributions to Hp,x=0.5E or excess molar internal energies at constant pressure, UV,x=0.5E. Calculated UV,x=0.5E for the present model systems are quite simple compared to the excess molar internal energy at constant pressure, UV,x=0.5E. They are very small in magnitude and show linear dependencies on the density of mixtures.