When granular materials with different properties (size, shape, density, etc.) flow, they tend to segregate. This research addresses a specific form of segregation (axial segregation) that occurs when size bidisperse granular mixtures flow inside a rotating cylindrical tumbler. Axial segregation is the formation of alternating bands of different particle species perpendicular to the axis of rotation. Axial bands form after a few rotations, typically first appearing at the tumbler endwalls and then progressively filling the tumbler via a process of successive nucleation from the interior edges of the innermost bands. At long times, O(100) rotations, bands tend to merge. Although the onset mechanism for axial band formation at the frictional endwalls of cylindrical tumblers is understood, there is, however, no well-accepted mechanism for axial band formation away from the endwalls or for the merging of axial bands. In this dissertation results from experiments and simulations examining axial band formation, and axial band merging under various endwall boundary conditions (frictional, frictionless, and spatially-periodic) and for various initial particle distributions (uniform, axisymmetric, and non-axisymmetric) in cylindrical tumblers are presented. An onset mechanism for axial bands at frictionless endwalls is proposed. Axial dispersion of a single isolated band of large particles in a bed of small particles is also examined to better understand the interaction of multiple bands for a range of particle size ratios, initial band widths, and fill fractions is also examined for low and high fill fractions. For isolated bands in tumblers that have a fill fraction of 50% by volume band spreading is diffusive after some transient period and this transient time is related to the size particle ratio and initial band width. For a fill fraction of 20% by volume isolated bands do not spread for a particle size ratio range of 1.5<R<2.25 with initial widths ranging from W_0 = 0.4 cm to W_0 = 4 cm in simulations. In experiments, this stability occurred only for W_0 = 4 cm, R=2, and for d_L =6 mm, 4 mm and 2 mm

Last modified

• 01/09/2019

Creator

• Darius B. Wheeler

DOI

• https://doi.org/10.21985/N2T18B

Subject

• Mechanical Engineering

Keyword

• Particle Physics

Date created

• 2017-01-01

Resource type

• Dissertation

Rights statement

• In Copyright