Wouter K. den Otter

Segregation of granular particles by mass, radius, and density in a horizontal rotating drum

The impact of particle properties on segregation and mixing of bidisperse granular beds in a rotating horizontal drum have been studied by discrete element method (DEM) simulations. Bidispersities in radius, density, and mass have pronounced influences on the stationary mixing pattern, although they hardly affect the granules’ flow regime. At 50% fill level, all beds mix well for a Froude number of approximately 0.56, corresponding to a flow regime intermediate to cascading and cataracting, while segregation occurs both at lower (rolling and cascading regime) and higher (cataracting/centrifuging regime) Froude numbers. These observations are explained qualitatively by noticing that the angular drum velocity dictates the flow regime, which in turn determines the effectiveness and direction of four competing (de)mixing mechanisms: random collisions, buoyancy, percolation, and inertia.


Wouter den Otter studied applied physics at the Eindhoven University of Technology (TUE), followed by a PhD in chemical physics at the University of Twente (UT) in Enschede. After a postdoc at the chemistry department of the University of Manchester Institute of Science and Technology (UMIST), he returned to Twente as postdoc and assistant professor in the computational biophysics group, and currently he is associate professor in the multiscale mechanics group. His research focuses on statistical mechanical simulations, studying various systems ranging from colloids, rods and polymers to proteins and granular matter, both in and out of equilibrium.