Oscillatory granular segregation in a long drum mixer

Khan, Zeina S.; Tokaruk, Wayne A.; Morris, Stephen W.

doi:10.1209/epl/i2003-10157-4

Cited by 60 publications

(51 citation statements)

References 25 publications

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“…In other systems, such as rotating drums [49,50,51], vibrated buckets [52,53], and draining silos [15], bidisperse granular materials display a tendency to segregate (rather than mix) during dynamics, but there is currently no general theory which could be applied to our reactor geometry. Therefore, our DEM simulations provide a useful means to address this important question.…”

Section: B Simulation Resultsmentioning

confidence: 99%

Analysis of granular flow in a pebble-bed nuclear reactor

et al. 2006

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Pebble-bed nuclear reactor technology, which is currently being revived around the world, raises fundamental questions about dense granular flow in silos. A typical reactor core is composed of graphite fuel pebbles, which drain very slowly in a continuous refueling process. Pebble flow is poorly understood and not easily accessible to experiments, and yet it has a major impact on reactor physics. To address this problem, we perform full-scale, discrete-element simulations in realistic geometries, with up to 440,000 frictional, viscoelastic 6cm-diameter spheres draining in a cylindrical vessel of diameter 3.5m and height 10m with bottom funnels angled at 30• or 60• . We also simulate a bidisperse core with a dynamic central column of smaller graphite moderator pebbles and show that little mixing occurs down to a 1:2 diameter ratio. We analyze the mean velocity, diffusion and mixing, local ordering and porosity (from Voronoi volumes), the residence-time distribution, and the effects of wall friction and discuss implications for reactor design and the basic physics of granular flow.

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Section: B Simulation Resultsmentioning

confidence: 99%

Analysis of granular flow in a pebble-bed nuclear reactor

et al. 2006

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“…Axial segregation has been extensively studied experimentally [5,6,7,8,9,10,11,12,13,14,15,16,17], numerically [18,19,20,21] and theoretically [22,23,24,25,26,27]. Yet, full understanding is still lacking.…”

Section: Introductionmentioning

confidence: 99%

Diffusion of a granular pulse in a rotating drum

Taberlet

Richard

2006

Phys. Rev. E

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The diffusion of a pulse of small grains in an horizontal rotating drum is studied through discrete elements methods simulations. We present a theoretical analysis of the diffusion process in a onedimensional confined space in order to elucidate the effect of the confining end-plate of the drum. We then show that the diffusion is neither subdiffusive nor superdiffusive but normal. This is demonstrated by rescaling the concentration profiles obtained at various stages and by studying the time evolution of the mean squared deviation. Finally we study the self-diffusion of both large and small grains and we show that it is normal and that the diffusion coefficient is independent of the grain size.

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“…Indeed, most experiments focus only on the free surface of the media, which is not satisfactory. It is experimentally possible (but difficult) to measure the subsurface concentrations using MRI [4] or optical techniques [6]. It is however impossible to identify the original location of a grain (i.e.…”

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confidence: 99%

Understanding the dynamics of segregation bands of simulated granular material in a rotating drum

2004

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PACS. 45.70.Mg -Granular flow: mixing, segregation and stratification. PACS. 83.10.Mj -Molecular dynamics in rheology.Abstract. -Axial segregation of a binary mixture of grains in a rotating drum is studied using Molecular Dynamics (MD) simulations. A force scheme leading to a constant restitution coefficient is used and shows that axial segregation is possible between two species of grains made of identical material differing by size. Oscillatory motion of bands is investigated and the influence of the frictional properties elucidated. The mechanism of bands merging is explained using direct imaging of individual grains.Introduction. -Among the many puzzling phenomena exhibited by granular media, axial segregation [1] aka. banding is one of the least understood. Due to the fundamental interest as well as the numerous industrial applications [2], a great deal of both experimental [3][4][5][6][7] and theoretical [7][8][9][10] work has been devoted to the topic, but full understanding is still lacking. Molecular Dynamics simulation provides new insights in the understanding of the phenomenon since it allows one to vary all parameters and measure any physical property. The only large scale numerical study of axial segregation [11] reports remarkable results but interactions between grains are derived from the Lennard-Jones potential, which is not well-suited for granular material. Our simulation uses a modified spring-dashpot force scheme leading to a restitution coefficient independent of the species of grains colliding. Here we show that axial segregation is possible between two species of grains made of identical material differing by size. We observe that a difference in the frictional properties of the two species of grain is not necessary to the onset of banding but does triggers oscillatory instabilities. Finally, the mechanism of bands merging is elucidated using direct imaging of individual grains. We also propose under which conditions coarsening may stop or slow significantly.

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Oscillatory granular segregation in a long drum mixer

Cited by 60 publications

References 25 publications

Analysis of granular flow in a pebble-bed nuclear reactor

Analysis of granular flow in a pebble-bed nuclear reactor

Diffusion of a granular pulse in a rotating drum

Understanding the dynamics of segregation bands of simulated granular material in a rotating drum

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