The modified Leung-Griffiths model of vapor-liquid equilibrium: Developments for binary mixtures of dissimilar fluids.

摘要

The modified Leung-Griffiths model is a corresponding states theory applied to mixtures that successfully correlates, evaluates, and predicts vapor-liquid equilibrium (VLE) boundaries for binary fluid mixtures. The strength of the model lies in its excellent performance at and near the critical locus down to about half of the critical pressures. Conventional phase equilibrium algorithms based on classical equations of state generally fail to converge or are inaccurate near the critical locus. The modified Leung-Griffiths model, however, incorporates nonclassical, scaling-law critical exponents. Because of the universality of critical behavior, the technique is relatively insensitive to phenomena such as polarity or hydrogen bonding which usually cause severe calculation problems.; This thesis covers several topics. The first is an investigation into some of the near-critical phenomena of binary fluid mixtures using asymptotic expansions. Dew-bubble curves are expanded through five orders about the critical locus within the formalism of the model. Explicit mathematical representations of the curves are obtained and the coefficients of the expansions are closely evaluated. Another subject, one that has had a significant impact on the progress of the remainder of the work, is the problem of fitting VLE data to non-linear functions. This problem is discussed and examples of systematic non-linear fits are presented. The next topic is the incorporation of "extended scaling," the Wegner correction, into the theory. This extension improves the performance of the model for binary mixtures with wide dew-bubble curves, that is mixtures with two highly dissimilar components. Finally, a study of the predictive capabilities and limitations of the model is presented.