Assessment of thermodynamic models via Joule–Thomson inversion

Abstract

The performance of thermodynamic models is assessed with respect to Joule–Thomson inversion on the basis of 29 fluids with varying molecular structure. Three thermodynamic model types are considered: classical force fields, the molecular-based PC-SAFT equation of state (EOS) and empirical multi-parameter EOS. The force fields consist of Lennard–Jones and multi-polar interaction sites and were evaluated by molecular dynamics simulation and integration of Mayer’s f function. The force fields and PC-SAFT were parameterized solely to vapor-liquid equilibrium data, while basically all available experimental thermodynamic property data have been used in the development of the empirical EOS. The fluids considered in this comparison comprise noble gases, triangular polar molecules, linear quadrupolar molecules, hydrogen boding molecules, cyclic alkanes, aromatics and siloxanes. It is found that the physically motivated models (force fields and PC-SAFT) provide throughout realistic predictions for the Joule–Thomson inversion curve. Upon extrapolation, about half of the empirical EOS yield reasonable results, the remainder show deficiencies. The three model types are in good mutual agreement at low and moderate temperatures, deviations are observed at high temperatures. In most cases, PC-SAFT systematically predicts a higher ideal gas limit temperature of the Joule–Thomson inversion curve than the force fields. By expressing the characteristic points of the Joule–Thomson inversion curve in terms of the critical temperature and pressure, the adequacy of the classical corresponding states principle is discussed.