(673b) Multilayer Granular Segregation in Discharging Cylindrical Hoppers
AIChE Annual Meeting
Thursday, November 2, 2017 - 8:18am to 8:36am
Manogna Adepu, Shaohua Chen, Yang Jiao, Aytekin Gel, Heather Emady
School for Engineering of Matter, Transport and Energy, Arizona State University, Tempe, AZ 85287
Particulate systems play a significant role in many industries, like pharmaceuticals, polymers, mineral processing, munitions, energy, food processing, environment, and agriculture. The discharging of granular materials from a hopper is a critical topic of industrial importance, and the discharge flow rate from hoppers is of continuous research interest. Granular materials typically consist of particles with a distribution of sizes, shapes, and densities, which may induce segregation of the material upon handling. Since the product quality is often contingent on maintaining blend homogeneity, segregation of granular materials is undesirable for many solids handling processes. Therefore, it is important to examine the causes and extent of segregation in various systems.
This work uses experiments to investigate the segregation of polydispersed silica particles during hopper discharge. The variables of interest here include the size distribution of particles and particle friction. A 3D printed lab scale hopper with four size ranges (diameters of 1.0-1.2 mm, 1.4-1.7 mm, 2.0-2.2 mm, and 3.7-4.0 mm) of silica particles is used for the study. The hopper is filled with the four layers of particles, starting with the fine layer on the bottom and finishing with the coarse layer on the top. The particles are discharged and collected transiently in equal volumes. Sieve analysis is done to analyze the weight fractions of all four layers. Preliminary results show that a central flow channel is formed, and the top layer begins to deflect and forms a âVâ-shaped surface. The incline formed promotes segregation via percolation whereby the fine layers shift downward into the inert or slow-moving material below, while coarse particles tend to roll down the incline toward the hopper centerline. As a result, the coarse layers start to discharge. Since the velocities are greatest near the centerline, the fines-depleted material that accumulates near the hopper centerline discharges quickly. As discharge continues, fines-rich material near the hopper walls is discharged, resulting in a peak at the end of the segregation profile, which is consistent with previous two-layer hopper segregation studies . The same batch of particles will be subjected to etching, thereby increasing the surface roughness. Those particles will be used to investigate the friction effects on segregation.
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