An equation of state for dipolar two-center Lennard–Jones molecules and its application to refrigerants

For two-center Lennard–Jones molecules with embedded point dipole (2CLJD-molecules) a hybrid equation of state for the Helmholtz energy F2CLJD is constructed as the sum of the Helmholtz energy F2CLJ for nonpolar two-center Lennard–Jones molecules and the dipolar contribution to the Helmholtz energy FD, F2CLJD=F2CLJ+FD. For pure fluids, predictions from this equation for the thermodynamic data of the homogeneous phase and for the vapour–liquid phase equilibria show good-to-excellent agreement with simulation data. To study deviations from the corresponding states theorem, acentric factors are calculated, and isoacentric curves are given as a function of the molecular elongation and the dipole strength. The equation is then used for a description of the real fluids R22 and R152a. Finally, it is shown that properties of model mixtures are also well predicted by using an appropriate mixing rule.