Correlations for Diffusivity

TABLE 5-18 Correlations for Diffusivities of Dilute/ Binary Mixtures of Nonelectrolytes in Liquids... 

Wilke, C. R. and Chang, P. (1955) AIChE Jl 1, 264. Correlation for diffusion coefficients in dilute solutions. 

Wilke (W8) has developed a correlation for diffusion coefficients on the basis of the Stokes-Einstein equation. His results may be summarized by the approximate analyti-... 

Oiffusivity The kinetic theory of liquids is much less advanced than that of gases. Therefore, the correlation for diffusivities in liquids is not as reliable as that for gases. Among several correlations reported, the Wilke-Chang correlation (Wilke and Chang, 1955) is the most widely used for dilute solutions of nonelectrolytes,... 

Correlations for Diffusion Coefficient Viscosity and Density of C09 Naphthalene Mixture "... 

Figure 2. Free volume correlation for diffusion as a function of temperature for methanol and acetone.

Diffusion of gases, vapors, and liquids in solids, however, is a more complex process than the diffusion in fluids because of the heterogeneous structure of the solid and its interactions with the diffusing components. As a result, it has not yet been possible to develop an effective theory for the diffusion in solids. Usually, diffusion in solids is handled by the researchers in a manner analogous to heat conduction. In the following paragraphs typical methods are described for the development of semiempirical correlations for diffusivity. 

Brown AM, Ashby MF (1980) Correlations for diffusion constants. Acta Metall 28 1085-1101... 

The Stokes-Einstein formula for diffusion coefficients is limited to cases in which the solute is larger than the solvent. Predictions for liquids are not as accurate as for gases. The Wilke and Chang [16] correlation for diffusion in liquids is an empirical correlation and is given by... 

Correlations for diffusion in gases, liquids, and solids were discussed. Which would be appropriate for liquid diffusing in a solid or gases diffusing in a liqnid ... 

This equation also finds use as a correlation for diffusion coefficients in solids. Tabulations of Dq and the activation energy E for various species can be found in the pertinent literature. An example of their application appears in Practice Problem 3.10. 

---