Studies on granular materials. V. Experimental determination of movement of granular materials mixed by a mechanical impeller

Novosád, Jan

doi:10.1135/cccc19684164

Cited by 18 publications

(12 citation statements)

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“…The motion and flow structure of granular materials with relative to the blade was studied in 3D by Stewart et al19 through PEPT measurements in a cylindrical mixer equipped with two opposing flat blades. The motion of particles was similar to that observed by other workers14–16 that at the wall the particles in the path of the blades are displaced upward forming a heap and then moved over the blades. Away from the wall, a fraction of the upwardly displaced material moved away from the blade down the faces of the heaps.…”

Section: Introductionsupporting

confidence: 85%

“…Earlier works in characterizing flow structure of an agitated powder bed were mainly conducted by photographing experiments through a transparent wall. A more detailed characterization of flow patterns is also possible by bed freezing (by solvent infiltration and setting) and dissection 14–16. Granular flow over a flat blade has been studied in two dimensions.…”

Section: Introductionmentioning

confidence: 99%

“…Granular flow over a flat blade has been studied in two dimensions. Bridgwater et al14 studied the horizontal and vertical displacements of single particle by one blade pass while Novosad15 studied the motion of particle in a vertical cylinder stirred by a long flat blade by dissecting beds of different colored layers that had been frozen using paraffin. In these studies, the authors observed the formation of a heap of particles moving just ahead of the blade, and the presence of a wake region with high bed porosity behind it.…”

Section: Introductionmentioning

confidence: 99%

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Granular flow fields in vertical high shear mixer granulators

Kwan

Ding

et al. 2007

AIChE Journal

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This study aims to elucidate some basic features of the granular flow field in a conical frustum-shaped vertical high shear mixer granulator by using the Positron Emission Particle Tracking technique. The tested range of particle size (d 50 ¼ 23, 43, and 60 lm) and shape as quantified by the angle of internal friction (268 and 388) have a negligible effect on the granular flow field in the mixer granulator. Density of particle imposes great influence on the flow field where reducing density from 2600 to 700 kg m 23 increase the tangential velocity by 1.95 time. Decreasing fill level from 3.5 to 0.9 kg increases the tangential velocity by a factor of 1.19. No obvious discrepancy in the solids motion is seen between machines of 1 and 5 L capacity and both machines have similar mixing and dispersion with constant tip speed criterion.

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Section: Introductionsupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Granular flow fields in vertical high shear mixer granulators

Kwan

Ding

et al. 2007

AIChE Journal

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“…Research at a particle scale has been recognised as a promising approach to overcome this di culty. In the past, such studies have to be made by bed freezing and dissection which is very laborious and su ers a great deal of uncertainty (Bridgwater and Bagster, 1968;Novosad, 1968;Bagster and Bridgwater, 1969;Malhotra et al, 1988). Recent studies in this area are mainly based on the newly developed advanced experimental or numerical techniques among which the so-called positron emission particle tracking (PEPT) Bridgwater et al, 1993) and discrete element method (DEM) (Cundall and Strack, 1979) are probably most representative.…”

Section: Introductionmentioning

confidence: 98%

Microdynamic analysis of the particle flow in a cylindrical bladed mixer

Zhou

Stewart

et al. 2004

Chemical Engineering Science

128

117

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“…A three dimensional visualisation method used by Novosad (1968) involved the dissection of a bed of different colour layers that had been frozen using paraffin. Though a crude and time consuming method, it found that the flow patterns observed at the wall were only qualitatively representative of the bulk powder.…”

Section: Techniques Of Studying Powder Flowmentioning

confidence: 99%

Powder flow in vertical high shear mixer granulators

Tran¹

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An integral component in understanding the fundamental mechanisms of granulation is the powder flow behaviour within mixer granulators. All three classes of granulation rate processes: wetting and nucleation, consolidation and coalescence, and attrition and breakage require detailed knowledge of flow fields in mixing systems to enable rational approaches to the prediction of granule attributes. The three objectives of this thesis are to 1) develop a powder flow regime map to characterise the powder flow field, 2) investigate the effect of impeller speed, powder cohesion and blade-rake angle on powder flow and mixing behaviour and, 3) outline a framework for compartment models of vertical-axis high shear mixer (vHSM) granulators.In the development of the powder flow regime map, two distinct regimes were identified. Ideal roping regime occurs at high impeller speeds when the rotating blades pushes the powder out and up the mixer wall, and then back down the free surface forming the "roping" flow pattern. This stable flow behaviour promotes high vertical bed turnover which is essential for controlled granulation. In this regime, the powder in the blade region has sufficient rotational inertia to overcome gravitational forces (i.e. powder Froude number greater than unity). If this criterion is not met, the mixing system remains in the undesirable bumping regime. This regime is characterised by poor bed turnover and non-uniform shear distribution within the powder bed. In the bumping regime, multiple transitional states are observed with increasing impeller speeds for this particular system, which has not been fully characterised in the literature before. An explanation for the observed apparent roping behaviour based on bed resonance is given. These intermediary transitional states can be differentiated by blade-powder interactions.From these observations, a powder flow regime map for vertical-axis mixer granulators is proposed based on two dimensionless groups: powder Froude number, the ratio of the powder rotational inertial to gravitational forces and the Bed Resonance number, which characterises the interaction of the bulk motion of the powder bed with the passage of impeller blades beneath it. The regime map was validated by experimental results utilising ii iii the well-established, non-invasive tracking technique of Positron Emission Particle Tracking (PEPT) and torque measurements.Investigations into the effect of impeller speed, powder cohesion and blade-rake angle on powder flow and mixing behaviour were conducted using PEPT. Results showed that powder velocity, bed porosity and shear rates varied spatially within the mixer granulator. Studies of the stable roping regime revealed that the average powder velocity in the impeller zone was 1.66 m/s (≈25% of the impeller tip speed). In comparison, the average powder velocity in the circulation and surface zone was approximately half of the impeller zone at 0.9 and 0.74 m/s, respectively (12% and 11% of the impeller tip speed). With the addition of mois...

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Studies on granular materials. V. Experimental determination of movement of granular materials mixed by a mechanical impeller

Cited by 18 publications

References 0 publications

Granular flow fields in vertical high shear mixer granulators

Granular flow fields in vertical high shear mixer granulators

Microdynamic analysis of the particle flow in a cylindrical bladed mixer

Powder flow in vertical high shear mixer granulators

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