Corresponding states principle pure fluid

The Corresponding-States Principle Dense Fluids Table 12.3. Sample results for pure fluid thermal conductivity. 

Thus far we have only introduced the pure-fluid corresponding-states principle which, as mentioned above, has a rigorous basis in molecular theory. The extension of this theory to mixtures cannot, however, be made without further approximation and the problem of rigorous, yet tractable, prediction of mixture properties remains unsolved. These approximations take the form of mixing rules which are the topic of Chapter 5 in this volume. We will only discuss mixing rules from an illustrative basis to show problems that can arise in the implementation of a corresponding-states model. In that regard, we will focus our discussions on the one-fluid theories and primarily the van der Waals one-fluid theory proposed by Leland et The essence of this model... 

Previous studies have shown that the approach is not very well suited for the prediction of excess properties especially if there are substantial differences in molecular size. Since the corresponding-states principle for pure fluids is exact, this failure can be attributed to a failure of the van der Waals one-fluid mixing rules to correctly map the composition dependence of higher-order temperature terms in the reference-fluid equation of state. Efforts like those of Estala-Uribe et are underway to develop more sophisticated mixing rules for cal-... 

Representation of mixtures is based on the one-fluid corresponding-states principle. Two steps are required to represent a mixture the mixture is first characterized as a hypothetical pure fluid and then the resulting hypothetical pure fluid is related to the reference fluid using equations (12.1) and (12.6). The mixing rules are... 

If the two-parameter theorem of corresponding states were generally valid, the slope S would be the same for all pure fluids. This is observed not to be true each fluid has its own characteristic value of S, which could in principle serve as a third corresponding-states parameter. However, Pitzer noted that all vapor-pressure data for the simple fluids (Ar, Kr, Xe) lie on tlie same line when plotted as log vs. 1/71 and that the line passes tlirough logi j. = —1.0 at Tr = 0.7. This is illustrated in Fig. 3.13. Data for other fluids define other lines whose locations can be fixed in relation to the line for the simple fluids (SF) by the... 

The determination of dense fluid properties from ab initio quantum mechanical calculations still appears to be some time from practical completion. Molecular dynamics and Monte Carlo calculations on rigid body motions with simple interacting forces have qualitatively produced all of the essential features of fluid systems and quantitative agreement for the thermodynamic properties of simple pure fluids and their mixtures. These calculations form the basis upon which perturbation methods can be used to obtain properties for polyatomic and polar fluid systems. All this work has provided insight for the development of the principle of corresponding state methods that describe the properties of larger molecules. 

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