#### Description

We computationally study the diffusion coefficient, D, in granular flows of monodisperse and bidisperse particles spanning regions of rapid, dense flow, and quasi-static creep flow in open and closed laterally confined heaps. Measurements of D at various flow rates, streamwise positions, and depths collapse onto a single curve when plotted as a function of g ̇d ̅ 2, where d is the local mean particle diameter and g ̇ is the local shear rate. When g ̇ is large, D is proportional to g ̇d ̅ 2, as in earlier studies. However, for g ̇d ̅ 2 below a critical value, D is constant. The acceleration of gravity and particle stiffness together determine the location of the transition in D between the shear-rate-dependent regime in rapid, dense flow and the shear-rate-independent regime in quasi-static creep flow. Our study supports earlier work showing that g –1 is the relevant time scale in rapid, dense flow; however, in quasi-static creep flow, the time scale depends instead on gravity √(d ̅/g) and the particle binary collision time. Funded by the Dow Chemical Company.

#### Recommended Citation

Umbanhowar, P.,
Ottino, J.,
Lueptow, R.,
&
Fan, Y.
(2014).
Shear-rate-independent collisional diffusion in granular materials.
In A. Bajaj, P. Zavattieri, M. Koslowski, & T. Siegmund (Eds.).
*
Proceedings of the Society of Engineering Science 51st Annual Technical Meeting, October 1-3, 2014
*,
West Lafayette: Purdue University Libraries Scholarly Publishing Services, 2014.
http://docs.lib.purdue.edu/ses2014/mss/mmpm/8

Shear-rate-independent collisional diffusion in granular materials

We computationally study the diffusion coefficient, D, in granular flows of monodisperse and bidisperse particles spanning regions of rapid, dense flow, and quasi-static creep flow in open and closed laterally confined heaps. Measurements of D at various flow rates, streamwise positions, and depths collapse onto a single curve when plotted as a function of g ̇d ̅ 2, where d is the local mean particle diameter and g ̇ is the local shear rate. When g ̇ is large, D is proportional to g ̇d ̅ 2, as in earlier studies. However, for g ̇d ̅ 2 below a critical value, D is constant. The acceleration of gravity and particle stiffness together determine the location of the transition in D between the shear-rate-dependent regime in rapid, dense flow and the shear-rate-independent regime in quasi-static creep flow. Our study supports earlier work showing that g –1 is the relevant time scale in rapid, dense flow; however, in quasi-static creep flow, the time scale depends instead on gravity √(d ̅/g) and the particle binary collision time. Funded by the Dow Chemical Company.