Suppressing the segregation of granular mixtures in rotating tumblers

Abstract

in Wiley InterScience (www.interscience.wiley.com).While an understanding of the dynamics of segregation has begun to emerge, controlling segregation continues to be a complicated problem. The use of time-modulation-via selective baffle placement-in order to suppress segregation in rotating tumblers is explored. Bidisperse (size or density), cohesionless granular materials in quasi-two-dimensional (2-D) rotating containers are studied by means of simulations and experiments. Results are presented in two main configurations for the placement of the baffles, (1) axial placement, and (2) attached to the periphery of the tumbler. Both experiments and simulations indicate that baffles attached at the periphery are ineffective in reducing segregation, while baffles axially located in the tumbler generate periodic flow inversions and dramatically reduce both density and size segregation. Qualitative and quantitative evidence is presented, in terms of the intensity of segregation. Theoretical and scale-up arguments are provided for the practical implementation of this approach.

Improvement of granular mixing of dissimilar materials in rotating cylinders

“…The flow remains steady for the no baffle system, but the flow becomes unsteady (i.e., periodic) in the presence of an axially placed baffle. Previously reported theoretical discussions [20,21] suggest that the axially-located baffle not only reduces the uninterrupted flow length of the shear layer material (lowering the time available to segregation), but also reorients the flow prior to its next pass through the layer (changing the effective direction of segregation). Here we investigate the mixing and segregation for both density and size segregation in a cylinder with and without a baffle at the axis of rotation for various system parameters.…”

“…Focusing specifically on the tumbler application, Vargas et al [21] reported that a single, passive baffle placed at the axis of rotation can eliminate segregation, while conventionally-placed baffles (i.e., those fixed at the periphery of the rotating cylinder) are ineffective. In this work, we aim to experimentally probe several aspects of this tumbler arrangement with the hope of determining design parameters of interest.…”

“…The positions are chosen relative to the undisturbed tumbler flow and represent: at the free surface, within the shear layer, and outside the shear layer. These choices are made primarily due to the fact that our previous theoretical analysis [21] suggests that disturbing the material within the shear layer is the critical operation in segregation reduction. In order to determine the position of the "shear layer", we experimentally measure the layer thickness at the midpoint (δ 0 ) for a flow with no baffle by observing streak-line photographs following the procedure of Ref.…”

Particle Mixing Study in Rotating Wavy Wall Tumblers by Discrete Element Method Simulation

“…1−7 Among the many important issues in particle mixing, particular attention has been paid to the effects of the geometric configuration of the mixer on particle mixing dynamics. For example, Vargas et al 8 explored the phenomena of suppression of segregation caused by time modulation of selective baffle placements in rotating drums. The influences of axial and peripheral placements of baffles were compared, and the former was found to reduce segregation drastically.…”

Convective heat transfer analysis in aggregates rotary drum reactor

“…Academic problem persists in tumbler such as the prediction of particle motion [2] including effect of cohesion, the heat and mass transfer rates [3], and the global internal heat exchanges. These phenomena are crucial in order to enhance heat and mass transfer and globally improve the performance of the rotary drum dryer.…”