Transport properties rough hard-sphere fluid

This direct proportionality between the rough hard-sphere transport properties and the Enskog coefficients has formed the basis for many correlations of liquid transport properties (Easteal Woolf 1984 Li etal. 1986 Walker etal. 1988 Greiner-Schmid et al 1991 Harris etal 1993). For a successful data fit, with unique values for Vq and the proportionality factors, it is necessary to fit a minimum of two prt rties simultaneously, with the same Vq values. This is exemplified in the case of methane in Chapter 10. It is further shown in Chapter 10 that successful correlation of transport property data for nonspherical molecular liquids can be made, based on the assumption that transport properties for these fluids can also be directly related to the smooth hard-sphere values. 

In the following section, expressions are given for the transport coefficients of dense as semblies of smooth hard-spheres and applied to the rare gases. The only adjustable parameter here is the core size. For molecular fluids, there is the possibility of translational-rotational coupling. The effects of this are discussed in Section 10.3 in terms of the rough hard-sphere model, which leads to the introduction of one additional parameter - the translational-rotational coupling factor - for each property, and the results are applied to methane. For dense nonspherical molecular fluids, it is assumed that the transport properties can also be related directly to the smooth hard-sphere values with proportionality factors ( roughness factors ) which account for effects of nonspherical shape. The application of this method is described in 10.4 with reference to alkanes, aromatic hydrocarbons, alkanols and certain other compounds. 

Unfortunately, real molecules differ significantly from hard spheres, so Equation (1.12) to (1.14) are not directly useful for real fluids. Additional correction factors can be added to these equations for fairly realistic spherically symmetric interactions these can represent nonpolar fluids that are roughly spherical, such as the noble gases and CH4. However, most molecules of interest are far from spherical, and kinetic theory is still intractable for molecular interactions that are not spherically symmetric. Therefore, the direct applicability of kinetic theory for calculating transport properties of real fluids is limited. However, kinetic theory plays an important role in guiding the functional form of semiempirical correlations such as those discussed below. 

Dense fluid transport property data are successfully correlated by a scheme which is based on a consideration of smooth hard-sphere transport theory. For monatomic fluids, only one adjustable parameter, the close-packed volume, is required for a simultaneous fit of isothermal self-diffusion, viscosity and thermal conductivity data. This parameter decreases in value smoothly as the temperature is raised, as expected for real fluids. Diffusion and viscosity data for methane, a typical pseudo-spherical molecular fluid, are satisfactorily reproduced with one additional temperamre-independent parameter, the translational-rotational coupling factor, for each property. On the assumption that transport properties for dense nonspherical molecular fluids are also directly proportional to smooth hard-sphere values, self-diffusion, viscosity and thermal conductivity data for unbranched alkanes, aromatic hydrocarbons, alkan-l-ols, certain refrigerants and other simple fluids are very satisfactorily fitted. From the temperature and carbon number dependency of the characteristic volume and the carbon number dependency of the proportionality (roughness) factors, transport properties can be accurately predicted for other members of these homologous series, and for other conditions of temperature and density. Furthermore, by incorporating the modified Tait equation for density into... 

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