Prediction of PVT Properties of Fluids Using FMSA EOS Based on L-J Potential Model

First-order mean spherical approximation (FMSA) equation of state (EOS) with two parameters for Lennard-Jones (L-J) fluid proposed by Tang has been studied in this article. This equation was used to predict the vapor-liquid phase coexisting diagrams, saturated vapor pressure profiles, and PVT properties of real fluids. The results of prediction were compared with literature data and those from three-parameter FMSA EOS. The two parameters of L-J potential model were determined with vapor-liquid phase coexistence data of the corresponding fluid at the reduced temperature Tr<0.95. For approximate spherical and non-polar molecular fluids, the equation can predict PVT properties of real fluids perfectly in wide ranges of temperature and pressure except near the critical region. The deviations of the predicted results were not sensitive to the size of the spherical molecules. The two-parameter FMSA EOS should not be applied to strong polar fluids. Calculations show that this function is superior to Peng-Robinson (P-R) equation at high density. For nonspherical molecular fluids, the results showed some evident deviations and were sensitive to the shape of molecules, which can be taken into consideration in the three-parameter FMSA EOS.