(673h) Quantification of Granular Size Segregation in a 3D Conical Bounded Heap: Theory, Simulations, and Experiments

Quantitative prediction of radial streamwise segregation in bounded conical heap flows of granular materials under a variety of flowrates and system sizes has yet to be demonstrated for problems at industry-scale, not least because of the difficulty in determining the kinematics below the free surface of an opaque material. We consider a continuum transport model for the local species concentration applied to the problem of particle segregation in an axisymmetric conical heap geometry. The continuum model is informed using mean-flow kinematics extracted from discrete element method (DEM) simulations with azimuthal periodic boundary conditions (to simulate an axisymmetric heap) for various flowrates, particle size ratios, and initial mixture concentrations. The DEM simulations are validated via comparison with experimental results for bidisperse streamwise segregation profiles and boundary kinematics obtained in a wedge-shaped conical flow apparatus with smooth walls. Although the measured streamwise segregation is qualitatively similar to previous results in quasi-2D bounded heaps at equivalent two-dimensional feed rates, key quantitative differences between the two geometries arise owing to differences in the mean velocity field and the local flowing layer depth, which varies non-trivially with radial distance away from the feed zone owing to the polar cylindrical geometry. To address this, we outline a method for incorporating the variable flowing layer thickness (whose scalings are provided by DEM) into a continuum advection-segregation-diffusion model, which is a necessary modification to the model to achieve quantitative agreement with measured segregation near the outer boundary wall. The continuum model also requires data for the species segregation velocity and diffusion coefficient, which depend on the local shear rate, particle concentration, and absolute particle diameters. Since the relations for the segregation velocity and diffusion coefficient are local, we use previous relations determined from quasi-2D bounded heap flows of bidisperse mixtures, which have also been shown to be applicable to other geometries. With the appropriate kinematic scalings incorporated, predictions from the continuum model show quantitative agreement with the steady-state radial streamwise segregation as measured in DEM simulations.

Funded by The Dow Chemical Company.