A micro-mechanical connection between the single-particle strength and the bulk strength of random packings of spherical particles

Ouwerkerk, Cor

doi:10.1016/0032-5910(91)80175-i

Cited by 51 publications

(32 citation statements)

References 11 publications

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“…Once a pre-specified strain has been achieved, the cell rotation is ceased. The prevailing shear stress causes attrition of the particles, the extent of which is known to be dependent on the magnitude of this stress and the applied strain (Paramanathan and Bridgwater, 1983b;Ouwerkerk, 1991;Neil and Bridgwater, 1994;Ghadiri et al, 2000).…”

Section: Methodsmentioning

confidence: 99%

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Prediction of attrition in agitated particle beds

Hare

Ghadiri

Dennehy

2011

Chemical Engineering Science

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The majority of pharmaceutical powders produced through crystallisation are dried in agitated dryers. The rotation of the impeller causes shear deformation of the bed, which enhances the drying rate, but also leads to particle breakage. A method of predicting the extent of breakage occurring due to agitation is described and applied for Paracetamol in a small-scale dryer. The distributions of stresses and strains in the bed are estimated using the Distinct Element Method (DEM). The information obtained here is then coupled with the measured attrition of Paracetamol in an annular shear cell in order to predict the attrition in the agitated bed. The experiments are carried out on dry material so as to establish purely the effect of stresses and strains on attrition, whilst keeping moisture content and temperature constant.The shear cell provides uniform condition for stresses and strains so that the breakage taking place under relatively well-defined conditions is quantified. In contrast, the prevailing shear stresses and strains in the agitated bed have wide distributions, as little shearing takes place near the impeller shaft, whilst there are considerable shearing stresses near the impeller tip. Therefore the bed is divided into a number of segments for which the extent of attrition can be evaluated for each segment, based on the shear cell data. A good quantitative agreement is found between the predictions and experimental results obtained for the attrition of Paracetamol in the small scale dryer. The resulting prediction also suggests that, for a given number of impeller rotations, the extent of breakage is independent of impeller speed in the range tested (20 -78 rpm). This is expected as the prevailing strain rates are too low for the inertial effects to be dominating and the shear stresses are independent of shear rates within the range investigated. The attrition prediction suggest that over half of the attrition occurs in the bottom third of the bed, with increased attrition at greater radial distances. The attrition is also predicted to occur predominantly 30 o in front of and behind the impeller.

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Section: Methodsmentioning

confidence: 99%

“…This equation was found to suitably describe attrition in a shear cell by Bridgwater (1989); however this approach does not take into account the effect of applied normal stress. Ouwerkerk (1991) found that the attrition of catalyst carrier beads could be best described by…”

Section: Methodsmentioning

confidence: 99%

Prediction of attrition in agitated particle beds

Hare

Ghadiri

Dennehy

2011

Chemical Engineering Science

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“…After unloading, the material is carefully removed from the cup and a gravimetric analysis is carried out to determine the amount of fines and broken particles. The BCS is defined as the pressure at which 0.5 mass% of fines smaller than 500 mm or broken material is produced [27].…”

Section: Bulk Crushing Strength Testmentioning

confidence: 99%

“…The facility of the University of Surrey is equipped with an annular shear cell, manufactured by Ajax Equipment Ltd. and based on a design [28]. The shear cell of the University of Surrey has moving walls which run at half the speed of the lower platen in order to improve the distribution of strains in the bed, following the work of Ouwerkerk [27]. A schematic diagram of the annular shear cell is presented in Figure 16.…”

Section: Shear Cell Testmentioning

confidence: 99%

Methodology for Investigating the Mechanical Strength of Reforming Catalyst Beads

Couroyer

Ghadiri

Laval³

et al. 2000

Oil & Gas Science and Technology - Rev. IFP

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Résumé -Méthodologie pour l'analyse de la résistance mécanique de billes de catalyseur utilisées dans le procédé de réformage catalytique -Les billes de catalyseur mises en oeuvre dans le procédé de réformage catalytique doivent présenter une résistance élevée pour faire face aux contraintes mécaniques et thermiques qu'elles subissent dans une unité de réformage à régénération continue. Un inventaire des contraintes mécaniques engendrées par le procédé et exercées par compression, lors d'impacts ou par cisaillement d'un lit de billes, montre qu'une approche « multitests » doit être adoptée pour évaluer la résistance des particules et ainsi, a posteriori, optimiser leur procédé de fabrication. Cette approche associe plusieurs tests reproduisant chaque type de contrainte engendrée et permet la détermination de caractéristiques mécaniques des particules poreuses, telles que le module de Young, la dureté et la ténacité. La méthodologie développée à partir de billes d'alumine va au-delà de la pratique courante d'évaluation de la résistance mécanique par les tests d'écrasement grain à grain et d'écrasement en lit. La détermination des propriétés individuelles des billes permet, en utilisant la méthode numérique des éléments distincts (DEA, Distinct Element Analysis), de prédire l'attrition dans un lit de catalyseur ou dans une cellule de cisaillement.Mots-clés : catalyseur, réformage catalytique, résistance mécanique, attrition. Abstract -Methodology for Investigating the Mechanical Strength of Reforming Catalyst Beads

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“…The contact forces that exist within these regions can lead to significant damage to the particles, ultimately resulting in an undesirable product and reduced efficiency of the process. Several empirical relationships have been developed to describe particle breakage as a function of applied stress and strain [2][3][4], using an attrition shear cell similar in design to that introduced by Paramanathan and Bridgwater [5].…”

Section: Introductionmentioning

confidence: 99%

Prediction of bulk particle breakage due to naturally formed shear bands

Hare¹,

Ghadiri²

2013

AIP Conference Proceedings

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Abstract. In many particle processes there exist both stagnant and flowing regions. Shear bands naturally form between these regions as a transition from zero to full velocity. Particles within shear bands are prone to breakage through surface erosion, chipping and fragmentation when exposed to substantial shear stresses. The precise nature and extent of breakage is difficult to describe mechanistically, due to the distribution of particle strengths and forces acting upon them. Consequently the breakage of particles within shear bands is typically defined empirically using an attrition shear cell. The use of such empirical relationships to predict breakage in larger processes is severely limited in the literature.This paper describes a method of predicting bulk breakage in an agitated vessel by establishing particle breakage caused by applied stress and strain in a shear cell. The Distinct Element Method (DEM) is utilised to estimate the distribution of stresses and strains within the agitated bed, this distribution is then applied to the breakage relationship to predict total attrition. The DEM analysis requires a number of measurement cells to be considered within the bed. It is imperative that the dimensions of these cells are comparable to that of a naturally occurring shear band. With this measure in place the method outlined here describes the experimental breakage well. This method can be applied to any system where particles break due to shear deformation.

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A micro-mechanical connection between the single-particle strength and the bulk strength of random packings of spherical particles

Cited by 51 publications

References 11 publications

Prediction of attrition in agitated particle beds

Prediction of attrition in agitated particle beds

Methodology for Investigating the Mechanical Strength of Reforming Catalyst Beads

Prediction of bulk particle breakage due to naturally formed shear bands

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