Avalanche mixing of granular solids

Metcalfe, Guy; Shinbrot, Troy; McCarthy, Joseph J.; Ottino, Julio M.

doi:10.1038/374039a0

Cited by 217 publications

(124 citation statements)

References 2 publications

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“…Radial segregation is a relatively fast process and occurs after a few revolutions of the drum. As a result of radial segregation larger particles are expelled to the periphery and a core of smaller particles is formed in the bulk (Khakhar et al, 1997;Metcalfe et al, 1995;Metcalfe and Shattuck, 1998;Ottino and Khakhar, 2000), see Fig. 10.…”

Section: Figmentioning

confidence: 99%

Patterns and collective behavior in granular media: Theoretical concepts

2006

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Granular materials are ubiquitous in our daily lives. While they have been a subject of intensive engineering research for centuries, in the last decade granular matter attracted significant attention of physicists. Yet despite a major efforts by many groups, the theoretical description of granular systems remains largely a plethora of different, often contradicting concepts and approaches. Authors give an overview of various theoretical models emerged in the physics of granular matter, with the focus on the onset of collective behavior and pattern formation. Their aim is two-fold: to identify general principles common for granular systems and other complex non-equilibrium systems, and to elucidate important distinctions between collective behavior in granular and continuum pattern-forming systems.

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Section: Figmentioning

confidence: 99%

Patterns and collective behavior in granular media: Theoretical concepts

2006

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“…In the cohesionless case, it is well known that as the drum rotational speed increases, the granular flow takes on one of a number of regimes such as slumping, rolling, cascading, cataracting, and centrifuging. All of these regimes can be characterized by the angle of repose or flowing speed by imaging techniques (Fischer et al, 2008;MiDi, 2004;Orpe and Khakhar, 2007). In the case of cohesive powders, the behavior of the granular assembly is more complex.…”

Section: Inroductionmentioning

confidence: 99%

“…Over the previous few decades, the overwhelming majority of the studies of such systems have focused on free-flowing or slightly cohesive materials (Castellanos et al, 1999;Castellanos et al, 2002;Fischer et al, 2008;Jiang et al, 2015;Metcalfe et al, 1995;MiDi, 2004;Orpe and Khakhar, 2007;Zhou and Sun, 2013).…”

Section: Inroductionmentioning

confidence: 99%

Granular dynamics of cohesive powders in a rotating drum as revealed by speckle visibility spectroscopy and synchronous measurement of forces due to avalanching

Yang

Jiang

Saw

et al. 2016

Chemical Engineering Science

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We have used speckle visibility spectroscopy (SVS) and synchronized force measurements to compare the granular dynamics of two cohesive lactose powders, with Sauter mean diameters of ~29 μm and ~151 μm, in a rotating drum. A load cell (LC) was used to measure forces on the drum mounting frame and enable monitoring of bulk powder motion; SVS is a dynamic light scattering technique particularly suited for studying dynamics in dense, non-ergodic granular systems. Our results reveal that surface slumping and intermittent collisional dynamics in the bulk of the bed are correlated, especially for the fine more cohesive particles (Geldart group C/A boundary), but not as much for the less cohesive larger particles (Geldart group A/B boundary). The specific dissipation energy of the particles in the drum is similar for both powders, and increases linearly with increasing drum speed. However, the dependencies of the load cell and SVS signals on rotation speed have opposing trends for these two powders, indicating different dissipation mechanisms for the different Geldart Groups; collisional dissipation is more important for the Geldart C/A powder, while for the Geldart A/B powder avalanche dissipation is dominant.

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“…Rotating drums and blenders (e.g. Metcalfe et al 1995, Shinbrot et al 1999, Hill et al 1999, Gray 2001 are often used in the pharmaceutical and food industry, while rotary kilns and inclined rotating cylinders (e.g. Davidson et al 2000, Spurling et al 2001) are favoured by chemical engineers for sintering, calcination, humidification, oxidation, drying, mixing, induration, reducing, gas-solid reaction, incineration, heating, cooling and cement production, because they allow continuous feed.…”

Section: Introductionmentioning

confidence: 99%

A three-phase mixture theory for particle size segregation in shallow granular free-surface flows

2006

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Particle-size segregation within granular materials is of great technological significance yet it is still very poorly understood. There are several causes for segregation, but this paper focuses on kinetic sieving which is the dominant mechanism in dense gravity-driven shallow free-surface flows, or, granular avalanches. The segregation model is derived from a three-phase mixture theory composed of large particles, small particles and a passive interstitial fluid. Steady-state solutions are constructed for a normally graded inflow in a steady uniform flow field. This problem is of fundamental interest, because it shows how an unstably stratified layer readjusts into a stable configuration. Expansion fans and concentration shocks are generated and sufficiently far downstream inversely-graded segregated layers form, with the larger particles overlying the finer ones. The distance for complete segregation to occur is shown to increase with rising fluid density and tends to infinity as its density approaches that of the grains. If the particles are buoyant then the initial configuration is stable. An exact time-dependent two-dimensional solution is constructed for plug-flow, which exploits the uncoupling of material columns of grains in the absence of shear. This yields insight into the nature of more complex numerical solutions for strong shear, which are computed with a high resolution, shock-capturing numerical scheme.

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Avalanche mixing of granular solids

Cited by 217 publications

References 2 publications

Patterns and collective behavior in granular media: Theoretical concepts

Patterns and collective behavior in granular media: Theoretical concepts

Granular dynamics of cohesive powders in a rotating drum as revealed by speckle visibility spectroscopy and synchronous measurement of forces due to avalanching

A three-phase mixture theory for particle size segregation in shallow granular free-surface flows

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