(85d) Granular Mixing In the Flowing Layer In Rotating Cylinders

Granular materials are widely used in industries such as iron & steel, mining, cement, construction, lime, fertilizers and pharmaceuticals. In order to design equipment such as rotary kilns, bins, silos, combustors, hoppers, chutes, hydro-cyclones, etc., in an effective and economical way, a thorough understanding of the various factors governing the flow characteristics of granular materials must be obtained. These needs have already motivated extensive analytical and experimental investigations of the flow of granular materials. Mixing is a central feature of many processes such as in the reduction of iron ore, cement clinkering, coal gasification, food processing, and tablet manufacturing. Ineffective mixing, or the inability to control particle segregation, is always costly in terms of rejected materials, extra blending time, and defective end products. Physical parameters that control the extent of mixing are not well-studied even in a simple geometry such as rotating cylinder. We study granular mixing in a rotating cylinder. A thin layer of particles in the free surface moves at very high velocity, whereas rests of the bed materials are rotated as a solid body rotation. Particles in the flowing layer experience a random motion due to inter particle collisions and this random motion causes the particles to diffuse in the transverse direction with respect to flow direction. Results of various parameters affecting the mixing will be presented. Role of particle size and cylinder speed of rotation on granular mixing will be discussed. Mixing is well-predicted with Lagrangian simulation based theory. Mixing in both radial and azimuthal directions will be discussed.