由L-J流体的FMSA状态方程计算流体的PVT性质

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

运用Tang等提出的Lennard-Jones(L-J)流体两参数的一阶平均球形近似(FMSA)状态方程,计算了流体的汽液共存相图和饱和蒸汽压曲线,以及非饱和区的PVT性质,并与文献数据进行比较.L-J参数由Tr<0.95的汽液相共存数据回归得到.计算结果表明,对于分子较接近球形的流体,除临界点附近外,该方程可以在较大的温度和压力范围内计算真实流体的PVT性质,结果满意.对于球形分子,该方程的精确度随分子尺寸的变大基本保持稳定.该方程不适用于强极性物质.在高密度区,该方程的计算结果明显优于P-R方程.对于分子偏离球形较远的流体,该方程的适用性变差,此时要考虑分子形状的影响,可采用三参数的FMSA状态方程进行计算.

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 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 deterrnined with vapor-liquid phase coexisting 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 for near the critical region. The deviations of the predicted results were not sensitive to the sizes 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.