Vapour-liquid equilibria for dipolar two-centre Lennard-Jones fluids by Gibbs-Duhem integration

Vapour-liquid equilibria for dipolar two-centre Lennard-Jones fluids having elongations L = 0.22, 0.3292, 0.505 and 0.67, and axial dipole moments μ∗ 2 = 2, 4, 8 and 12 are determined by the Gibbs-Duhem integration method. Starting coexistence points of the Gibbs-Duhem integrations are obtained by the Maxwell construction. Critical temperatures and densities are estimated from the law of rectilinear diameter and the critical scaling relation. Calculated vapour pressures as well as vapour and liquid densities are correlated by Wagner equations. The dipole moment increases the critical temperature and pressure, and affects slightly the critical density. The dipole moment provokes deviations from the principle of corresponding states. The temperature-density coexistence envelope is broadened and the slope of the vapour pressure curve increases with the dipole moment. Application of vapour-liquid equilibria of the dipolar two-centre Lennard-Jones fluids to real fluids is demonstrated on the alternative refrigerant HFC-134a.