Mixing processes for agricultural and food materials: 3. Powders and particulates

Abstract

Mixing of solid particulate materials is a common and ancient operation. The factors and methods relating to mixing of solid materials have been reviewed. Considering the wide application, the amount of information available appears quite limited. There is a general understanding of what happens in the process, but the details of forces and mechanisms have not been completely elucidated and developed into design procedures. Inter-particle percolation is an important mechanism in solids mixing. Mixing of solids is often accomplished by manipulating material flows or by use of simple tumblers. Ribbon impellers or large, open augers in vessels are sometimes utilized. The vessels may be open or closed, horizontal or vertical and may be cylindrical or some other shape such as conical with the impeller inclined. Total mixed rations for livestock are composed of materials with diverse characteristics. Mixing, and prevention of segregation of such materials are problems. Standard methods for evaluating the performance of mixing equipment have been developed. Tracers are added to a standard mixture and then the coefficient of variation determined for a series of samples. There is a need to develop methods for determining when mixing is satisfactorily completed.