Effect of humidity on triboelectric charging in a vertically vibrated granular bed: Experiments and modeling

Kolehmainen, Jari; Sippola, Petteri; Raitanen, Oskari; Özel, Ali; Boyce, Christopher M.; Saarenrinne, Pentti; Sundaresan, Sankaran

doi:10.1016/j.ces.2017.08.006

Cited by 39 publications

(31 citation statements)

References 50 publications

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“…The change of charge polarity in the experimental bed at approximately 30 % RH was unexpected, opposing our previous results obtained in vibrated bed experiments with similar particles (Kolehmainen et al 2017b); this difference is probably due to different glass material (borosilicate) or different carrier gas (air) used in the earlier experiments. A humidity-dependent reversal of polarity has been earlier observed by Mehrani et al (2007) for fines entrained from a fluidized bed of polyethylene particles.…”

Section: Discussioncontrasting

confidence: 55%

“…The model is based on the effective work function difference between materials and takes into account the electric field at the contact point, which has been shown to impact insulator triboelectrification (Zhou et al 2014;Mizutani et al 2015). The model has also showed good agreement with experimental results in vibrated bed experiments (Laurentie et al 2010(Laurentie et al , 2013Kolehmainen et al 2017b); in a granular hopper chute flow (Naik et al 2015); and in granular binary mixtures (Naik et al 2016).…”

supporting

confidence: 61%

“…Although lowering the acceleration factor results in less pronounced charge segregation, even an acceleration factor as low as a = 2 does not properly predict agglomeration of multiple layers on the wall. This is attributed to the fact that the charging model tends to over-predict the charging rate in the first place, which was also observed in our previous experiments with a vibrated bed (Kolehmainen et al 2017b). The underlying assumptions of the surface state model may explain the discrepancy between the simulated and experimental charging rates: for example it is assumed that the particles are perfectly spherical, but in reality charge localization at the asperities of the surfaces can significantly alter the electric field in the contact gap and hence the charging rate.…”

Section: Discussionmentioning

confidence: 60%

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Experimental and numerical study of wall layer development in a tribocharged fluidized bed

Sippola

Kolehmainen

Özel³

et al. 2018

J. Fluid Mech.

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The effects of triboelectricity in a small-scale fluidized bed of polyethylene particles were investigated by imaging the particle layer in the vicinity of the column wall and by measuring the pressure drop across the bed. The average charge on the particles was altered by changing the relative humidity of the gas. A triboelectric charging model coupled with a computational fluid dynamics-discrete element method (CFD-DEM) model was utilized to simulate gas-particle flow in the bed. The electrostatic forces were evaluated based on a particle-particle particle-mesh method, accounting for the surface charge on the insulating walls. It was found that simulations with fixed and uniform charge distribution among the particles capture remarkably well both the agglomeration of the particles on the wall and the associated decrease in the pressure drop across the bed. With a dynamic tribocharging model, the charging rate had to be accelerated to render the computations affordable. Such simulations with an artificial acceleration significantly over-predict charge segregation and the wall becomes rapidly sheeted with a single layer of strongly charged particles.

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Section: Discussioncontrasting

confidence: 55%

supporting

confidence: 61%

Section: Discussionmentioning

confidence: 60%

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Experimental and numerical study of wall layer development in a tribocharged fluidized bed

Sippola

Kolehmainen

Özel³

et al. 2018

J. Fluid Mech.

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“…In the present study, we are interested in analyzing particle charging resulting from contact with bounding surfaces made of a different material, and so we do not pursue these alternate approaches and focus on effective work function based models for triboelectrification. Work function based model of Laurentie et al (2013) has been used previously to describe triboelectrification of granular material in both gas-solid flows (Kolehmainen et al 2017a) and granular systems (Laurentie et al 2010;Naik et al 2015Naik et al , 2016Kolehmainen et al 2017b). This model takes into account the electric field at the contact point, which has been shown to impact insulator triboelectrification (Zhou et al 2014;Mizutani et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Eulerian modelling of gas–solid flows with triboelectric charging

Kolehmainen

Özel²,

Sundaresan

2018

J. Fluid Mech.

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Particles subjected to flow are known to acquire electrostatic charges through repeated contacts with each other and with other surfaces. These charges alter gas-particle flow behavior at different scales. In this work, we present a continuum framework for analyzing the interplay between tribocharging and flow of monodisperse assembly of particles characterized by a single effective work function. Specifically, we have derived the continuum, kinetic theory transport equations for gas-particle flow and local-averaged charge on particles directly from the Boltzmann equation. We also derive the auxiliary conditions to capture tribocharging at bounding conducting walls. The resulting two-fluid model with tribocharging and boundary condition has then been validated against results from discrete element simulations that have been specially designed to probe specific terms in the models.

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“…The triboelectric charging is modeled by following Laurentie et al [28], in which the charge transfer is driven by a difference in effective work function ϕ that depends on the materials under consideration and the electrical potential difference between the contacting surfaces. This charging model has been found to capture particle charging in a granular chute [29] and in a vibrated granular bed [28,30]. In this model, the effective work function is a lumped parameter that can be determined either empirically [28] or using density functional theory [29].…”

mentioning

confidence: 99%