Analysis of ball indentation on cohesive powder beds using distinct element modelling

Pasha, Mehrdad; Hare, Colin; Hassanpour, Ali; Ghadiri, Mojtaba

doi:10.1016/j.powtec.2012.08.017

Cited by 36 publications

(26 citation statements)

References 13 publications

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“…Although other methods of characterizing powder flow behavior at low stresses and under dynamic conditions have been reported (Hassanpour and Ghadiri, 2007;Wang et al, 2008, Pasha et al, 2013and 2015, but for moist powders and continuous shearing rheometer has better control over the test conditions. However, similar to the techniques suggested by above authors, the continuous shearing provided by rheometer can be carried out at low normal stresses applicable to some industrial operations conditions, e.g.…”

Section: Accepted M Manuscriptmentioning

confidence: 99%

Rheology of moist food powders as affected by moisture content

2016

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Dynamic testing to determine rheological characteristics of moist food powders (semolina, coarse wheat flour, potato starch) was carried out using a powder rheometer of a new construction. The unique feature of the rheometer is that scale of shearing was confined to the thickness of shearing band of powder bed only. It was found that flow pattern of moistened samples was noticeably and diversely affected by both moisture content (varying in the range of 0-15% w/w) and shear rate. The observed changes showed statistical significance p<0.01 in all trials carried out. What is noteworthy about the conducted research is that at some shear rate values, the shear stress of the bed reached the maximum for specific moisture content levels, irrespective of particle size of the bed.

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Section: Accepted M Manuscriptmentioning

confidence: 99%

Rheology of moist food powders as affected by moisture content

2016

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“…Work reported in the literature so far suggests that the shear stress is constant in the slow, frictional regime, gradually increases with strain rate in the intermediate regime, and rapidly increases in the dynamic regime. In tandem to the requirement of powder flow characterisation in the dynamic range of strain rates, there is also a great need to develop techniques for measuring powder flow at low levels of consolidation stress, as relevant to feeding operations for dry powder inhalers, capsules and tabletting shoes (Pasha et al, 2013;Wang et al, 2008;Wu and Guo, 2012) and for quality by design for formulations (Leturia et al, 2014). Bulk powder flow under dynamic conditions and the associated rheology has been analysed by Campbell (2004;, Delannay et al (2007), Jop et al (2006), Koval et al (2009) and Pouliquen et al (2006).…”

Section: Introductionmentioning

confidence: 99%

Analysis of powder rheometry of FT4: Effect of air flow

Nan

Ghadiri

Wang

2017

Chemical Engineering Science

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Understanding of particle flow behaviour as a function of strain rate is of great interest in many items of equipment of industrial processes, such as screw conveyors, impeller mixers, and feeders, etc. The traditional commercial instruments for bulk powder flow characterisation, such as shear cells, operate at low shear strain rates, and are not representative of unit operations under dynamic conditions. In recent years, the FT4 powder rheometer of Freeman Technology has emerged as a widely used technique for characterising particle flow under dynamic conditions of shear strain rate; yet little is known about its underlying powder mechanics. We analyse the effect of gas flow on the flow behaviour of cohesionless particles in FT4 both experimentally and by numerical simulations using the combined discrete element method (DEM) and computational fluid dynamics (CFD). The results show that the effect of gas flow on the flow energy could be described by the resultant fluid-induced drag on the particles above the blade position as the impeller penetrates the bed. The strain rate in front of the blade is mainly determined by the impeller tip speed, and is not sensitive to the gas flow and particle size. The flow energy correlates well with the shear stress in front of the blade. They both increase with the strain rate and are significantly reduced by the upward gas flow.

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“…The bed was consolidated to 10 kPa, then indented by a spherical indenter with a diameter of 16 times the particle length. These dimensions meet the criteria for minimum bed and ball diameter [6].…”

Section: Ball Indentationmentioning

confidence: 99%

The influence of aspect ratio and roughness on flowability

Hare¹,

Ghadiri²

2013

AIP Conference Proceedings

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Abstract. Poor flowability hampers particle processing in many instances; causing a reduction in process efficiency, increased manufacturing costs and leading to excessive waste. The resistance of powders to flow can arise from a number of particle properties, such as cohesion, friction, shape and roughness. The objective of this work is to determine to what extent the flowability of powders is affected by their particle shape and roughness. The Distinct Element Method (DEM) is used to precisely control the shape and roughness of the particles. Needle-like particles are represented by the method of overlapping spheres, introduced by Favier et al. (1999). The fractional overlap of these spheres is varied, along with the number of spheres per particle, to produce particles with ranges of roughness and aspect ratio, respectively. The flowability of these particles is assessed by simulating two systems: a standard shear box, and indentation of a powder bed with a spherical indenter -introduced by Hassanpour and Ghadiri (2007). The particles are generated with a random orientation and allowed to settle under gravity before they are consolidated by a platen to a desired stress. The results show that particles with a large aspect ratio experience reduced shear stresses. This behaviour may be caused by particles aligning, thus allowing them to slide past one another more easily. An increase in particle roughness promotes interlocking, for a given aspect ratio rougher particles are shown to experience increased shear stresses. This work provides a robust analysis of the influence of aspect ratio and roughness on the flowability of powders, thus allowing the flowability of real materials to be better understood.

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Analysis of ball indentation on cohesive powder beds using distinct element modelling

Cited by 36 publications

References 13 publications

Rheology of moist food powders as affected by moisture content

Rheology of moist food powders as affected by moisture content

Analysis of powder rheometry of FT4: Effect of air flow

The influence of aspect ratio and roughness on flowability

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