Influence of molecular potential type on the accuracy of virial equation of state in describing PVT relations of high temperature and high pressure gas

Abstract

In order to compare the influence of two commonly used molecular potentials: L-J (Lennard-Jones) 6-12 potential and EXP-6 (exponential-6) potential on the accuracy of calculating pressure-volume-temperature (PVT) relations of high temperature and high pressure gas by high order virial equation of state (EOS). In this paper, using the Kihara’s calculation method, the third order dimensionless virial coefficients of EXP- 6 potential (α=12) and EXP-6 potential (α=13) in dimensionless temperature T* =1- 500 are calculated. Using the orthogonal integration method proposed by Barker, the fourth and fifth order dimensionless virial coefficients of L-J 6-12 potential, EXP-6 potential (α=12) and EXP-6 potential (α=13) in T* =1-500 are calculated. By fitting these theoretical values, the corresponding high order virial EOS: VLJ, VEXP612 and VEXP613, are established. Using VLJ, VEXP612 and VEXP613 EOS to calculate the PVT relations of methane, oxygen, carbon dioxide and carbon monoxide under high temperature and high pressure, the accuracy and applicability of the two molecular potentials in the description of PVT relations of high temperature and high pressure gases are analyzed and evaluated by comparison. On this basis, the characteristics of intermolecular interaction in high temperature and high pressure gas are further analyzed.