Underlying Asymmetry within Particle Size Segregation

Vaart, Kasper van der; Gajjar, Parmesh; Épely-Chauvin, Gaël; Andreini, Nicolas; Gray, J.O.; Ancey, Christophe

doi:10.1103/physrevlett.114.238001

Cited by 107 publications

(176 citation statements)

References 41 publications

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“…Both of the time-averaged concentration plots indicate a 'tail' upstream, where the concentration is lower due to the slow motion of a few large grains. This is similar to asymmetric behaviour observed within a linear shear cell (van der Vaart et al 2015), and motivates a continuum breaking wave structure with an asymmetric flux function, shown in (e) for a cubic flux. The solid lines mark the boundaries of the recirculation zone, with two distinct 'lens' and 'tail' regions (see § 2).…”

Section: Recirculating Particle Motionmentioning

confidence: 51%

“…Asymmetry between large and small particle motion Recent experiments by Golick &Daniels (2009) andvan der Vaart et al (2015) have uncovered an underlying asymmetry in the behaviour of large and small grains during segregation, with a characteristic dependence on the local relative volume fraction of small particles. Within their annular ring shear experiments, Golick & Daniels (2009) inferred that large particles were segregating very slowly in regions of many small particles, but were not able to further explain this observation.…”

Section: 3mentioning

confidence: 99%

“…The individual motion of the particles on the centre line was revealed using refractive index matched scanning ('RIMS': Wiederseiner et al 2011a;Dijksman et al 2012;van der Vaart et al 2015). Spherical borosilicate glass beads of density 2230 kg m −3 and diameters 14 and 5 mm were used, with the volume ratio of large particles to small particles being 2 : 5.…”

Section: Recirculating Particle Motionmentioning

confidence: 99%

“…Small gaps in the grain matrix allow the finer grains to preferentially percolate downwards under gravity, whilst there is a return flow of coarse grains towards the surface. The exact mechanism for the rising of large grains is under investigation (van der Vaart et al 2015), although the net result is an upward coarsening in the particle-size distribution that is often called inverse grading. For example, a bidisperse mixture containing just two grain sizes would separate into two separate layers in the absence of diffusion, with the large particles on top of the small ones, as shown in figure 2(a).…”

Section: Introductionmentioning

confidence: 99%

“…The presence of the 'tail', in which large particles recirculate very slowly through regions of many small particles, points towards a fundamental asymmetry in the interactions between the large and small particles. Recently, van der Vaart et al (2015) uncovered a similar asymmetry in a linear shear cell, and showed how the asymmetry could be modelled using a continuum approach.…”

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confidence: 99%

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Asymmetric breaking size-segregation waves in dense granular free-surface flows

et al. 2016

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Debris and pyroclastic flows often have bouldery flow fronts, which act as a natural dam resisting further advance. Counter intuitively, these resistive fronts can lead to enhanced run-out, because they can be shouldered aside to form static levees that self-channelise the flow. At the heart of this behaviour is the inherent process of size segregation, with different sized particles readily separating into distinct vertical layers through a combination of kinetic sieving and squeeze expulsion. The result is an upward coarsening of the size distribution with the largest grains collecting at the top of the flow, where the flow velocity is greatest, allowing them to be preferentially transported to the front. Here, the large grains may be overrun, resegregated towards the surface and recirculated before being shouldered aside into lateral levees. A key element of this recirculation mechanism is the formation of a breaking size-segregation wave, which allows large particles that have been overrun to rise up into the faster moving parts of the flow as small particles are sheared over the top. Observations from experiments and discrete particle simulations in a moving-bed flume indicate that, whilst most large particles recirculate quickly at the front, a few recirculate very slowly through regions of many small particles at the rear. This behaviour is modelled in this paper using asymmetric segregation flux functions. Exact non-diffuse solutions are derived for the steady wave structure using the method of characteristics with a cubic segregation flux. Three different structures emerge, dependent on the degree of asymmetry and the non-convexity of the segregation flux function. In particular, a novel 'lens-tail' solution is found for segregation fluxes that have a large amount of non-convexity, with an additional expansion fan and compression wave forming a 'tail' upstream of the 'lens' region. Analysis of exact solutions for the particle motion shows that the large particle motion through the 'lens-tail' is fundamentally different to the classical 'lens' solutions. A few large particles starting near the bottom of the breaking wave pass through the 'tail', where they travel in a region of many small particles with a very small vertical velocity, and take significantly longer to recirculate. †

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Section: Recirculating Particle Motionmentioning

confidence: 51%

Section: 3mentioning

confidence: 99%

Section: Recirculating Particle Motionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Asymmetric breaking size-segregation waves in dense granular free-surface flows

et al. 2016

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Simulation and modeling of segregating rods in quasi‐2D bounded heap flow

et al. 2017

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Many products in the chemical and agricultural industries are pelletized in the form of rod-like particles that often have different aspect ratios. However, the flow, mixing, and segregation of non-spherical particles such as rod-like particles are poorly understood. Here, we use the discrete element method (DEM) utilizing super-ellipsoid particles to simulate the flow and segregation of rod-like particles differing in length but with the same diameter in a quasi-2D one-sided bounded heap. The DEM simulations accurately reproduce the segregation of size bidisperse rod-like particles in a bounded heap based on comparison with experiments. Rod-like particles orient themselves along the direction of flow, although bounding walls influence the orientation of the smaller aspect ratio particles. The flow kinematics and segregation of bidisperse rods having identical diameters but different lengths are similar to spherical particles. The segregation velocity of one rod species relative to the mean velocity depends linearly on the concentration of the other species, the shear rate, and a parameter based on the relative lengths of the rods. A continuum model developed for spherical particles that includes advection, diffusion, and segregation effects accurately predicts the segregation of rods in the flowing layer for a range of physical control parameters and particle species concentrations.

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Modeling granular material blending in a rotating drum using a finite element method and advection‐diffusion equation multiscale model

Gonzalez

Wassgren

2018

AIChE Journal

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A multiscale model is presented for predicting the magnitude and rate of powder blending in a rotating drum blender. The model combines particle diffusion coefficient correlations from the literature with advective flow field information from blender finite element method simulations. The multiscale model predictions for overall mixing and local concentration variance closely match results from discrete element method (DEM) simulations for a rotating drum, but take only hours to compute as opposed to taking days of computation time for the DEM simulations. Parametric studies were performed using the multiscale model to investigate the influence of various parameters on mixing behavior. The multiscale model is expected to be more amenable to predicting mixing in complex geometries and scale more efficiently to industrial-scale blenders than DEM simulations or analytical solutions. V C 2018 American Institute of Chemical Engineers AIChE J, 00: 000-000, 2018

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Underlying Asymmetry within Particle Size Segregation

Cited by 107 publications

References 41 publications

Asymmetric breaking size-segregation waves in dense granular free-surface flows

Asymmetric breaking size-segregation waves in dense granular free-surface flows

Simulation and modeling of segregating rods in quasi‐2D bounded heap flow

Modeling granular material blending in a rotating drum using a finite element method and advection‐diffusion equation multiscale model

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