Goodness of mixing

However, for many applications we do not need such a complete characterization of the state of the mixture in practice, simple methods often suffice. Commonly used methods, for example, are color comparison to a standard for qualitative visual homogeneity, or the measurement of some representative physical property. Between the two extremes of complete characterization and qualitative or semiqualitative practical evaluation, there is room for sound quantitative methods of characterization. We must keep in mind, however, that the goodness of mixing is not absolute, but dependent on the required needs. 

Danckwerts expresses the goodness of mixing by two statistically defined quantities, the scale and the intensity of segregation. He states that his treatment is suitable chiefly for mixtures where the smallest particles capable of independent movement are very small compared to the size of the portions which will normally be taken for use or analysis. For his analysis, he assumes that the mixture is uniform in texture that is, it cannot be divided into two parts of equal size in which the mean concentration or the scale or intensity of segregation differ significantly. He further states This is the most important limitation on the practical value of the definitions and tests which will be proposed. He emphasizes the fact that large scale segregation, caused for example by... 

When two viscous liquids are mixed, the interfacial area increases and the striation thickness decreases. Spencer and Wiley [201] have proposed to use the interfacial area as a quantitative measure of the goodness of mixing. Mohr et al. [189] used the striation thickness to describe the mixing process. If a surface element with arbitrary orientation is located in a simple shear flow field, the surface area A after a total shear strain of y can be demonstrated to be [201] ... 

In experimental studies, however, the striation concept is not often used. This has to do with the difficulty in accurately determining the number of striations beyond the level of coarse mixing. Another measure of mixing is the coefficient of variation (COV), discussed earlier. The COV has been used in several experimental studies to compare the goodness of mixing in various static mixers. 

The important aspect in mixing is to evaluate the quality of mixtures [2] or the goodness of mixing [3]. The most straightforward method of characterizing tiie quality of the mixtures is to measure to what extent the desired properties have been attained. Industrial quality control follows that route whenever feasible. However, this requires a detailed... 

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