(99d) Radial Segregation of Granular Materials in Rotating Cylinders

Flowing granular mixtures segregate, and this can have a significant impact in many industrial processes ranging from pharmaceutical tablet manufacturing to cement production. Rotating cylinders are used as kilns, mixers, dryers and granulators. However, when mixtures of two different types of particles are rotated in a rotating cylinder then they tend to segregate/demix. Segregation is studied in a rotating cylinder for mixtures of different size particles. In most of the systems studied, the measured radial weight fraction profiles in the bed show significant double segregation (a core of small particles as well as a thin layer of small particles at the periphery). The profiles are found to be sensitively dependent on the surface roughness of the particles in the mixture, and double segregation reduces with particle roughness. Double segregation is observed for all cylinder fill fraction. Double segregation is found decreased with increasing the cylinder speed of rotation and no double segregation is observed at higher cylinder speed of rotation. A continuum based model is developed and a good agreement is obtained.