(129g) The Mechanism behind Axial Segregation of Granules in a Horizontal Rotating Drum

Mixing of granules with different size, density, or shape is a common and important unit operation in the chemical, food and pharmaceutical industries. However, the phenomena at the basis of the mixing process are poorly understood. Operations intended for mixing may even result in segregation. Probably, the most general known segregation phenomena are the radial and axial segregation in a horizontal rotating drum. Since axial segregation is always preceded by radial segregation, knowledge about axial segregation will provide insight in radial segregation. We therefore studied the mechanism behind axial segregation in a horizontal rotating drum with various particle-based numerical simulations, covering a wide range of system parameters. Several existing theories were tested against the simulation results and found to be only partially satisfactory. A new hypothesis to explain the axial segregation is proposed that describes the broad range of observed processes in literature and in our simulations.