461959 Experimental and Numerical Study of Granular Size Segregation in 3D Bounded Wedge Flows

Tuesday, November 15, 2016: 10:00 AM
Peninsula (Hotel Nikko San Francisco)
Austin B. Isner1, Adithya Shankar1, Julio M. Ottino1, Paul B. Umbanhowar2 and Richard M. Lueptow2, (1)Chemical and Biological Engineering, Northwestern University, Evanston, IL, (2)Mechanical Engineering, Northwestern University, Evanston, IL

Segregation due to particle size in flowing granular materials is an important phenomenon observed in a wide variety of industrial flows—in particular, hopper filling and discharge. As a bidisperse mixture is continuously fed onto a heap, small particles percolate downward between large particles within a thin flowing layer (order O(10) particle diameters) and are deposited upstream onto the static heap, whereas large particles segregate to the top of the free surface and are advected downstream. The final segregation pattern is determined by the mass flow rate and width of the silo, as well as the particle size ratio. A recent continuum size segregation model quantitatively agrees with experimental spatial segregation patterns for bidisperse granular mixtures in simple quasi-two-dimensional (quasi-2D) heaps, where span-wise gradients in the velocity field are neglected. The generalization of this model to fully 3D geometries like cylindrical silos remains unclear. In this study, we investigate the kinematics and scaling behavior of flow during heap formation in an intermediate three-dimensional (3D) bounded wedge geometry, which introduces non-trivial divergence in the advection term involving the flow velocity. Results from 3D heap flow experiments of mono- and bidisperse granular mixtures in this geometry are compared and validated with numerical data from discrete element method simulations (DEM) for a range of wedge angles, feed rates, and particle mixtures. Frictional wedge sidewalls produce non-uniform azimuthal variation in concentration profiles consistent with results from DEM simulations using frictional sidewalls. Azimuthally periodic boundary conditions were also implemented in the DEM simulations and seem to accurately reflect a fully 3D bounded heap. Key considerations concerning the use of the 3D bounded wedge as an experimental tool in the study of segregation in a fully axisymmetric heap geometry are highlighted. Funded by The Dow Chemical Company.

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