Comprehensive study of the vapour-liquid equilibria of the pure two-centre Lennard-Jones plus pointdipole fluid

Abstract

Results of a systematic investigation of the vapour-liquid equilibria of 38 individual two-centre Lennard-Jones plus axial pointdipole model fluids (2CLJD) are reported over a range of reduced dipolar momentum 0 $\le \mu^{*2} \le$ 20 and of reduced elongation 0 $\le$ L* $\le$ 1.0. Temperatures investigated are from about 55 % to about 95 % of the critical temperature of each fluid. The NpT+Test Particle Method is used for the generation of vapour pressures, saturated densities, and saturated enthalpies. For the lowest temperatures, these data are calculated with highly accurate chemical potentials obtained from the gradual insertion method. Critical temperatures $T*_c$ and densities $\rho*_c$ are obtained from Guggenheim's equations. Empirical correlations for critical data $T*_c$ and $\rho*_c$ as well as for saturated densities $\rho'*$, $\rho''*$, and vapour pressures $p*_\sigma$ are developed as global functions of the model parameters. They describe the simulation data generally within their statistical uncertainties. Critical pressures and acentric factors of the 2CLJD fluid can be calculated from these correlations. The present results are a sound basis for adjustments of the model parameters $\mu^{*2}$, $L*$, $\sigma$, and $\epsilon$ to experimental VLE data of real fluids.