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Agglomeration and de-agglomeration of rotating wet doublets

Published online by Cambridge University Press:  21 August 2012

Carly M. Donahue ,
William M. Brewer ,
Robert H. Davis  and
Christine M. Hrenya
Carly M. Donahue
Affiliation:
Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309-0424, USA
William M. Brewer
Affiliation:
Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309-0424, USA
Robert H. Davis
Affiliation:
Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309-0424, USA
Christine M. Hrenya*
Affiliation:
Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309-0424, USA
*
†Email address for correspondence: [email protected]
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Abstract

In this work, experiments using a pendulum apparatus were conducted for two particles engaged in oblique, wetted collisions over a range of impact angles, impact velocities, coating thicknesses, liquid viscosities, particle materials, and particle radii. From previous studies on normal or head-on collisions, the two particles bounce apart if the Stokes number (a ratio of particle inertia to viscous forces) exceeds a critical value, whereas they stick together if the Stokes number is below this critical value. However, for oblique collisions, an additional outcome is observed at moderate Stokes numbers and impact angles, in which the spheres initially stick together, rotate as a doublet, and then separate due to centrifugal forces. We refer to this outcome as ‘stick–rotate–separate’. For subcritical Stokes numbers exhibiting this new outcome, the experimental results for the apparent coefficient of normal restitution and angle of rotation from impact to separation show only weak dependence on the fluid viscosity and thickness and the dry restitution coefficient, whereas they both decrease with increasing particle radius. These results are in contrast with those for supercritical Stokes numbers in which the spheres bounce upon impact. An accompanying theory based on lubrication forces, the glass transition of the liquid layer, and solid deformation and rebound agrees well with experimental results and gives insight into the observed trends.

JFM classification

Granular media: Granular media Low-Reynolds-number flows: Lubrication theory Multiphase and Particle-laden Flows: Particle/fluid flow
Type
Papers
Information
Journal of Fluid Mechanics , Volume 708 , 10 October 2012 , pp. 128 - 148
Copyright
Copyright © Cambridge University Press 2012

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