Cohesive grains: Bridging microlevel measurements to macrolevel flow behavior via surface roughness

Liu, Peiyuan; LaMarche, Casey Q.; Kellogg, Kevin M.; Leadley, Stuart R.; Hrenya, Christine M.

doi:10.1002/aic.15383

Cited by 23 publications

(15 citation statements)

References 59 publications

(73 reference statements)

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“…Similarly, as shown in Figure , the distance between the two rough spherical particles is the distance z 0 plus twice the radius of the asperity (suppose that the surface of particle is covered with hemispherical asperities of equal radii). Thus, on the basis of Rumpf theory, a model, applied to quantify the van der Waals force between two rough spherical particles with the same size, is given by

F_{vdW} = \frac{A d_{normalp}}{24 {true(z_{0} + 2 r true)}^{2}} + \frac{A d^{'}}{6 {true(z_{0} + r true)}^{2}} + \frac{A r}{12 z_{0}^{2}}

where

d^{'} = \frac{2 r d_{normalp}}{d_{normalp} + 2 r}

, the asperity of the particle is also considered as a semisphere, r is the radius for the semisphere asperity, and z 0 is also taken as 0.4 nm . In the above model, the van der Waals force consists of the attraction between two spheres, the attraction between the asperity and the other sphere, and the attraction between the asperities.…”

Section: Resultsmentioning

confidence: 99%

“…To predict the van der Waals force of particles with asperities, appropriate simplification for the asperities is required. Consequently, Rumpf and Rabinovich treated surface roughness as hemispheres and submerged spheres, respectively. And our model is based on the hemispherical asperity assumption.…”

Section: Resultsmentioning

confidence: 99%

“…But so far there have been few reports on the model of van der Waals force between two rough particles. Recently, a rigorous method, which did not rely on arbitrary or visual means, was proposed by Liu et al and LaMarche et al to predict adhesion force between two rough particles accurately. A methodology was established to separate the large‐ and small‐scale roughness, and to quantify the surface roughness using the parameters (RMS height and wavelength).…”

Section: Introductionmentioning

confidence: 99%

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Gravitational discharge of fine dry powders with asperities from a conical hopper

Zhong

Cao

et al. 2017

AIChE Journal

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The effects of particle properties, especially the surface roughness and particle type, on the gravity discharge rate and flow behavior of fine dry powders from a conical hopper are studied in detail. The van der Waals force is considered to dominate the discharge of small particles, while the empty annulus effect dominates the discharge of large particles. To predict the van der Waals force between two rough spherical particles, a model based on Rumpf theory is adopted. The effect of surface roughness can be reflected by Bond number Bo g which is correlated with discharge rate. By modifying the powder bed porosity and Beverloo constant, the discharge rates of fine dry powders can be well predicted by an empirical correlation. Finally, not only the ratio of hopper outlet size to particle size D 0 /d p but also the Bond number Bo g is found to be an important indicator to determine the powder flowability.

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F_{vdW} = \frac{A d_{normalp}}{24 {true(z_{0} + 2 r true)}^{2}} + \frac{A d^{'}}{6 {true(z_{0} + r true)}^{2}} + \frac{A r}{12 z_{0}^{2}}

where

d^{'} = \frac{2 r d_{normalp}}{d_{normalp} + 2 r}

Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Gravitational discharge of fine dry powders with asperities from a conical hopper

Zhong

Cao

et al. 2017

AIChE Journal

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show abstract

“…15 In addition to experiments, computer simulations based on the discrete element method (DEM) can be used to glean physical insight into the flow behavior of cohesive solids. [19][20][21] Furthermore, such roughness is typically irregular, making its incorporation into DEM nontrivial. However, the validation of DEM simulations via direct comparison with experiments-that is, without resorting to assumed or fitted parameters for the cohesion model-remains rare.…”

Section: Introductionmentioning

confidence: 99%

“…Such roughness cannot be ignored due to the high sensitivity of cohesion to the minimum particleparticle separation distance, which is controlled by surface roughness. [19][20][21] Furthermore, such roughness is typically irregular, making its incorporation into DEM nontrivial. Several attempts have been made to model the surface roughness as regular geometrical features-for example, hemispheres, 22 spherical caps with two lengths scales, 23,24 and a asperity distribution function.…”

Section: Introductionmentioning

confidence: 99%

A square‐force cohesion model and its extraction from bulk measurements

et al. 2018

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Accurate modeling of interparticle forces in DEM is critical to predicting the rheology of cohesive particles. Rigorous cohesion models usually include parameters associated with particle surface roughness. However, both roughness measurement and its distillation into appropriate model parameters remain challenging. We propose a square‐force cohesion model, where cohesive force remains constant until a cutoff separation, above which cohesion vanishes. We demonstrate the square‐force model is a valid surrogate of more rigorous models. Specifically, when two parameters of square‐force model are chosen to match the two key quantities governing dense and dilute flows, namely maximum cohesive force and critical cohesive energy, respectively, DEM results using square‐force and more rigorous models show good agreement. For practical application of the square‐force model to lightly cohesive systems, a method is established to extract its parameters via defluidization, enabling determination of particle–particle cohesion from simpler bulk measurements than complicated and expensive scans on individual grains. © 2018 American Institute of Chemical Engineers AIChE J, 64: 2329–2339, 2018

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How nano‐scale roughness impacts the flow of grains influenced by capillary cohesion

et al. 2017

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SignificanceWe show that nano-scale changes in surface roughness affect the macro-scale (many-particle) behavior of granular materials influenced by cohesion. Macro-scale effects of roughness are investigated for conditions where cohesion is dominated by either humidity-induced or van der Waals-induced forces. Surface-topography measurements are used to calculate the relevant interparticle cohesive forces. The (force-dominated) macro-scale cohesion measurements are explained via the ratio of the predicted interparticle cohesive force to gravity, thus reinforcing the importance of roughness to cohesion.The values of u mf plotted in (b) are extracted from (a). Increasing cohesion (via a decrease in roughness or an increase in RH) results in a decrease in the slope of Dp* vs. u in the packed state-such that a statistically significant increase in u mf /u mf,NC is measured between the particles both at dry and humid conditions. Error bars represent 95% confidence intervals, but may be too small to distinguish on the scale of the plot. [Color figure can be viewed at wileyonlinelibrary.com] AIChE Journal

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Cohesive grains: Bridging microlevel measurements to macrolevel flow behavior via surface roughness

Cited by 23 publications

References 59 publications

Gravitational discharge of fine dry powders with asperities from a conical hopper

Gravitational discharge of fine dry powders with asperities from a conical hopper

A square‐force cohesion model and its extraction from bulk measurements

How nano‐scale roughness impacts the flow of grains influenced by capillary cohesion

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