Characteristic curves of the stockmayer fluid: Molecular simulation and equation of state modeling

Molecular-based equation of state (EOS) models are an important tool for modeling thermophysical properties of fluids. Many fluids exhibit dipolar interactions for which Helmholtz energy models have been developed. The extrapolation behavior of these dipole contributions is critical for the extrapolation behavior of the total EOS model. In this work, nine dipole contribution models from the literature were examined regarding their performance on Brown's characteristic curves. The zero-density limit of Brown's curves are directly related to the second virial coefficients. Therefore, also the second virial coefficient was evaluated. The evaluation of the dipole contribution models was carried out using the Stockmayer model fluid. Therefore, all considered dipole contribution models were combined with an accurate Lennard-Jones EOS. Molecular simulations were used for determining reference data for the characteristic curves. Important differences are obtained for the extrapolation behavior of the different dipole contribution models. For low dipole moments, all studied dipole contribution models yield correct characteristic curves. With increasing dipole moment, some dipole contribution models yield unphysical artifacts.