Effects of size and density differences on mixing of binary mixtures of particles

Mixing of granular materials is an important operation in many industries such as the pharmaceutical industry. Generally, a granular material to be mixed can have particles of different densities and sizes, which makes the mixing difficult. Several studies have addressed the issue of finding the optimum combinations of the size and density ratios of binary particles for mixing to happen, using rotating drums as the mixers. For mixtures of particles uniform in either the size or density, we have shown previously that mixing index of the mixtures can be represented by a unique function of the variable, γβ³ where β (<1) and γ (<1) are the size and density ratios respectively. This concept was demonstrated for a volume fraction, α = 0.5 of the large (or denser) particles, using a vertically shafted cylindrical mixer. The implication of this result is that the size effects can be represented by an equivalent density difference. Here, this concept is further investigated for mixing of binary particles having different combinations of β and γ, at different values of α. It is shown that the variation of the mixing index can be expressed as a function of the three variables, β, γ and α Such a relationship will be useful in predicting the outcomes of mixing of binary particles.