Size-Dependent Same-Material Tribocharging in Insulating Grains

Waitukaitis, Scott; Lee, Victor; Pierson, James; Forman, Steven L.; Jaeger, Heinrich M.

doi:10.1103/physrevlett.112.218001

Cited by 135 publications

(127 citation statements)

References 45 publications

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“…Thus, the particle tracking during freefall was essentially a diagnostic of the triboelectric or contact charging that had occurred during earlier particle-particle contacts, most likely inside the hopper during the outflow process. Waitukaitis et al (2013;2014) were able to show that such contact charging among particles made from the same material involves the transfer of negative charge and that the charging magnitude can be linked directly to the dispersion in particle size, as proposed earlier by Lacks et al (2007;2008). Particles smaller than the mean size tend to become charged negatively, while larger particles tend to acquire positive charge.…”

Section: Clusters and Cohesive Forcesmentioning

confidence: 59%

“…We note that polarization forces are always attractive, irrespective of the charge polarity on the participating particles. For single-peaked particle size distributions, where the peak of the associated charge distribution from collisions will be near zero charge (Waitukaitis et al (2014), this means that clusters will tend to be comprised of (near) neutral particles that have aggregated around highly charged ones.…”

Section: Clusters and Cohesive Forcesmentioning

confidence: 99%

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Small-Scale Particle Interactions Are Having Significant Effects on Global Fluidized Bed Behavior

Cocco

Issangya

Karri

et al. 2017

KONA

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Fluidized bed design and scale-up depends strongly on particle characteristics such as size, shape, and for Geldart Group A particles, the level of fines (particles smaller than 44 microns). However, recent research has shown that particle clustering has a significant effect on fluidized bed hydrodynamics which impacts how these units should be designed and scaled up. This is especially true with the estimation of the solids entrainment rate and the cyclone collection efficiency. The amount of fines, particle shape and surface morphology play a role on the level of particle clustering in a fluidized bed. The fine particles are an excellent conduit for moving charge as electrons or ions which appear to be the dominant mechanism of electrostatics for Geldart Group A material in a bubbling fluidized bed. This electrostatic force trades off with particle momentum relaxation and rotational to translation momentum transfer with regard to forming a particle cluster. The issue is the quantification of this effect so more precise calculations can be made with particle entrainment rates and cyclone collection efficiency. Preliminary work on particle shear in a packed and fluidized beds, suggest that particle clustering can be measured and may provide a quantifiable metric for the level of particle clustering.

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Section: Clusters and Cohesive Forcesmentioning

confidence: 59%

Section: Clusters and Cohesive Forcesmentioning

confidence: 99%

Small-Scale Particle Interactions Are Having Significant Effects on Global Fluidized Bed Behavior

Cocco

Issangya

Karri

et al. 2017

KONA

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“…Past studies have largely focused on geometric or material differences between grains [13][14][15][16][17]. Remarkably, however, grains that are absolutely identical in shape, size and chemical composition have also been found to charge one another [16,[18][19][20][21][22][23][24].…”

Section: Introductionmentioning

confidence: 99%

Field driven charging dynamics of a fluidized granular bed

et al. 2016

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A simplified model has previously described the inductive charging of colliding identical grains in the presence of an external electric field. Here we extend that model by including heterogeneous surface charge distributions, grain rotations and electrostatic interactions between grains. We find from this more realistic model that strong heterogeneities in charging can occur in agitated granular beds, and we predict that shielding due to these heterogeneities can dramatically alter the charging rate in such beds.

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“…This distribution is the result of a very large number of collisions and sliding/rubbing events among particles during sample preparation and outflow from the vessel 20 . It arises from tribocharging between grains of identical material, and thus statistically similar surface density of transferable charges, but slightly different surface area 9,21,22 . Overall charge is conserved and the distribution is centred around zero.…”

mentioning

confidence: 99%

“…In particular, for a bimodal P(q) with positive and negative peaks roughly symmetric around zero, we would expect typical cluster configurations in which contacting grains exhibit alternating polarity. Recent experiments have demonstrated that such a P(q) can be achieved by mixing bidisperse same-material grains 22 . The P(q) for such a mixture using diameters 326 ± 10 µm and 251 ± 10 µm is shown in Fig.…”

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confidence: 99%

Direct observation of particle interactions and clustering in charged granular streams

et al. 2015

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Clustering of fine particles is of crucial importance in settings ranging from the early stages of planet formation [1][2][3] to the coagulation of industrial powders and airborne pollutants [4][5][6][7] . Models of such clustering typically focus on inelastic deformation and cohesion 1,4,6,8 . However, even in charge-neutral particle systems comprising grains of the same dielectric material, tribocharging can generate large amounts of net positive or negative charge on individual particles, resulting in long-range electrostatic forces [9][10][11] . The e ects of such forces on cluster formation are not well understood and have so far not been studied in situ. Here we report the first observations of individual collide-and-capture events between charged submillimetre particles, including Kepler-like orbits. Charged particles can become trapped in their mutual electrostatic energy well and aggregate via multiple bounces. This enables the initiation of clustering at relative velocities much larger than the upper limit for sticking after a head-on collision, a long-standing issue known from pre-planetary dust aggregation 1,12 . Moreover, Coulomb interactions together with dielectric polarization are found to stabilize characteristic molecule-like configurations, providing new insights for the modelling of clustering dynamics in a wide range of microscopic dielectric systems, such as charged polarizable ions, biomolecules and colloids [13][14][15][16] . One of the key difficulties in studying the interplay between repulsive contact forces, short-range cohesion and long-range electrostatic forces during cluster formation has been to obtain sufficiently detailed experimental data. Seeing how this process unfolds demands in situ observation of the collision trajectories among charged grains to extract quantitative information about their interactions. This requires the grains to be freed from gravity and tracked with high spatial and temporal resolution to capture individual collision events 17,18 . We overcome these obstacles with the set-up shown in Fig. 1a (refs 19,20). The granular material, in our experiments fused zirconium dioxide-silicate grains a few hundred micrometres in diameter, is contained in a vessel mounted inside a 3.0-m-tall cylindrical chamber. We evacuate this chamber to mitigate air drag. When a shutter covering a small orifice at the bottom of the vessel is opened, particles fall out freely, forming a dilute stream. Outside the chamber, a high-speed video camera falls alongside the grains, guided by low-friction rails. In the co-moving frame seen by the camera, the effect of gravity is eliminated, making it possible to track particle interactions in detail for about 0.2 s until the camera is decelerated by a foam pad. The same apparatus also allows determination of the net charge on individual grains: during free fall a horizontal electric field can be applied and the resulting horizontal acceleration observed by the camera gives the charge to mass ratio, q/m.Using particles with a narrow size d...

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Size-Dependent Same-Material Tribocharging in Insulating Grains

Cited by 135 publications

References 45 publications

Small-Scale Particle Interactions Are Having Significant Effects on Global Fluidized Bed Behavior

Small-Scale Particle Interactions Are Having Significant Effects on Global Fluidized Bed Behavior

Field driven charging dynamics of a fluidized granular bed

Direct observation of particle interactions and clustering in charged granular streams

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