How rotational vortices enhance transfers

Griffani, D.; Rognon, Pierre; Metzger, Bloen; Einav, Itai

doi:10.1063/1.4817671

Cited by 25 publications

(20 citation statements)

References 33 publications

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“…random variable drawn from the two integer values {−1,1} and ⇔ represents the swapping of values in respective cells. The mixing rate is set to allow random swapping of grains either up or down with diffusion rate r D = D /(2 Δ W 2 ), where Δ W 2 is the mean square displacements over which the motion fluctuates [ Campbell , ; Griffani et al , ] and D is the granular diffusivity (m 2 /s). This is known to scale as

D \propto | \overset{γ}{true} |

for both collisional [ Savage and Dai , ] and dense [ Utter and Behringer , ] flows, where

\overset{γ}{true}

is the local shear strain rate (s −1 ).…”

Section: Resultsmentioning

confidence: 99%

A mixture of crushing and segregation: The complexity of grainsize in natural granular flows

Marks

Einav

2015

Geophysical Research Letters

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The interplay between grain crushing and segregation controls the dynamics of dense granular flows that underpin many natural hazards. We address this issue for the first time by developing a simple lattice model with three interacting rules—for grain crushing, mixing, and segregation. In earthquake faults, particles are trapped, they crush and mix, but do not segregate. In this case the model produces power law distributions, consistent with previous models. When segregation by kinetic sieving is added to the model, we predict depth‐dependent lognormal distributions as previously observed, but not explained, in pyroclastic flows, debris flows, rock avalanches, and dry snow avalanches.

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D \propto | \overset{γ}{true} |

for both collisional [ Savage and Dai , ] and dense [ Utter and Behringer , ] flows, where

\overset{γ}{true}

is the local shear strain rate (s −1 ).…”

Section: Resultsmentioning

confidence: 99%

A mixture of crushing and segregation: The complexity of grainsize in natural granular flows

Marks

Einav

2015

Geophysical Research Letters

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“…60,61 The velocity of nonequilibrium EOF, proportional to the magnitudes of the local tangential and normal electric fields, dominates the size and velocity field of the vortex pairs, while the size of a vortex pair can be restricted by the finite space of the microchannel. Second, we ignore any minor changes in the thickness of the electric field-induced depleted DL, 26 but consider the major changes in the thickness of the depleted DL affected by fluid flow, which are observed in our experiment.…”

Section: Control Volume Model For Five-stage Preconcentration Processmentioning

confidence: 99%

Real-time dual-loop electric current measurement for label-free nanofluidic preconcentration chip

et al. 2015

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An electrokinetic trapping (EKT)-based nanofluidic preconcentration device with the capability of label-free monitoring trapped biomolecules through real-time dual-loop electric current measurement was demonstrated. Universal current-voltage (I-V) curves of EKT-based preconcentration devices, consisting of two microchannels connected by ion-selective channels, are presented for functional validation and optimal operation; universal onset current curves indicating the appearance of the EKT mechanism serve as a confirmation of the concentrating action. The EKT mechanism and the dissimilarity in the current curves related to the volume flow rate (Q), diffusion coefficient (D), and diffusion layer (DL) thickness were explained by a control volume model with a five-stage preconcentration process. Different behaviors of the trapped molecular plug were categorized based on four modes associated with different degrees of electroosmotic instability (EOI). A label-free approach to preconcentrating (bio)molecules and monitoring the multibehavior molecular plug was demonstrated through real-time electric current monitoring, rather than through the use of microscope images.

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“…For instance, granular vortices induce some mixing of grains between the streamlines, a process referred to as shearinduced diffusion [1,[3][4][5]. And most astonishingly, they were found to strongly enhance the efficiency of granular media to transfer heat across the flows by the means of granular convection [5,6].…”

mentioning

confidence: 98%

A circulation-based method for detecting vortices in granular materials

2015

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Dense granular flows exhibit large clusters of grains rotating in correlated fashions. We present a method to identify and quantify such granular vortices, based on the circulation of velocity fluctuations around closed curves. Here, the method is applied on physical experiments of twodimensional granular flows in the Stadium Shear Device geometry. Results illustrate how the method is capable to capture the positions, sizes, velocities and life-times of individual vortices. The method should be useful for many purposes, including: (1) complementing existing ways for defining typical correlation lengths in granular systems; (2) studying the kinematics behind the superior efficiency of granular systems to transfer of mass, heat and momentum when compared with other fluids; and (3) characterising vortices in other particulate fluid systems such as suspensions, emulsions and foams, which exhibit similar velocity patterns.

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How rotational vortices enhance transfers

Cited by 25 publications

References 33 publications

A mixture of crushing and segregation: The complexity of grainsize in natural granular flows

A mixture of crushing and segregation: The complexity of grainsize in natural granular flows

Real-time dual-loop electric current measurement for label-free nanofluidic preconcentration chip

A circulation-based method for detecting vortices in granular materials

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