Prediction of impeller torque in high shear powder mixers

Knight, P.C.; Seville, Jonathan; Wellm, A.B; Instone, T.

doi:10.1016/s0009-2509(01)00114-2

Cited by 102 publications

(82 citation statements)

References 14 publications

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“…It has been reported by Knight et al 9) that the frictional force made a significant contribution to the total torque when using low-angle beveled blades. As mentioned above, the effect of the rotational speed of flat blades on the torque in this study-where torque increased significantly at the higher rotational speedcorresponds to the results for flat blades obtained by Knight et al 9) However, Knight et al did not show the powder flow patterns or velocity distributions in their paper. As Knight 10) suggests that both blade shape and rotational speed are important variables in a high shear mixer, the dry powder motion was observed visually using PEPT in the present study in order to investigate the effects of rotational speed and blade type on the flow of the material.…”

Section: Resultssupporting

confidence: 85%

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Three-Dimensional Visualization of Powder Motion in a High Shear Mixer

et al. 2011

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Section: Resultssupporting

confidence: 85%

“…Knight et al 9) also found that torque varied considerably with both the height and bevel angle of the blades in the vertical high shear mixer. In their study, the torque value of flat blades increased linearly with an increase of blade speed at speeds above 100 rpm.…”

Section: Resultsmentioning

confidence: 94%

Three-Dimensional Visualization of Powder Motion in a High Shear Mixer

et al. 2011

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“…In some cases the rotating axis does not revolve but it is the vessel that rotates (Boerefijn et al, 2009). Despite the large use of this type of granulators in many industrial processes, the agglomeration mechanisms caused by liquid binder addition are currently not totally understood (Laurent, 2005;Knight et al, 2001). Granulation can be indeed affected by a large number of variables, including process parameters, material properties and formulation variables (Faure et al, 2001).…”

Section: Introductionmentioning

confidence: 99%

Texture analysis as a tool to study the kinetics of wet agglomeration processes

Nalesso

Codemo

Franceschinis

et al. 2015

International Journal of Pharmaceutics

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In this work wet granulation experiments were carried out in a planetary mixer with the aim to develop a novel analytical tool based on surface texture analysis. The evolution of a simple formulation (300 g of microcrystalline cellulose with a solid binders pre-dispersed in water) was monitored from the very beginning up to the end point and information on the kinetics of granulation as well as on the effect of liquid binder amount were collected. Agreement between texture analysis and granules particle size distribution obtained by sieving analysis was always found. The method proved to be robust enough to easily monitor the process and its use for more refined analyses on the different rate processes occurring during granulation is also suggested.

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“…. , Plank et al, 2003, c) Niro Pellmix (Knight et al, 2000, Schaefer et al, 1993, d) Collette Gral (Faure et al, 1999), e) Zanchetta (Nilpawar et al, 2006), f) custom design vHSM (Tu et al, 2009, Knight et al, 2001, Bridson et al, 2007, g) planetary mixer (Hiseman et al, 2002), and h) cyclomix mixer granulator (Ng et al, 2007a) 6.1 Properties of each compartment from experimental PEPT data for the two-CM and multi-CM: occupied volume vol, occupancy occ, average particle velocity v p , average dimensionless particle velocity v …”

Section: Granulation Processes As Classified Bymentioning

confidence: 99%

“…Fielder, Diosna, Collette Gral, Niro Pellmix (Knight et al, 2000, Schaefer et al, 1993, though other studies also include the cyclomix (Ng et al, 2007a,b, Hassanpour et al, 2009) and planetary mixer (Hiseman et al, 2002) (see Figure 1.5). A number of researchers have designed custom mixers in order to simplify complex flow , Plank et al, 2003, c) Niro Pellmix (Knight et al, 2000, Schaefer et al, 1993, d) Collette Gral (Faure et al, 1999), e) Zanchetta (Nilpawar et al, 2006), f) custom design vHSM (Tu et al, 2009, Knight et al, 2001, Bridson et al, 2007, g) planetary mixer (Hiseman et al, 2002), and h) cyclomix mixer granulator (Ng et al, 2007a) Knight et al (2000) patterns (see Figure 1.6). However, many studies are still carried out at very low impeller speeds which are not directly relevant to industrial practices (Stewart et al, 2001a).…”

Section: Granulation Equipmentmentioning

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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Prediction of impeller torque in high shear powder mixers

Cited by 102 publications

References 14 publications

Three-Dimensional Visualization of Powder Motion in a High Shear Mixer

Three-Dimensional Visualization of Powder Motion in a High Shear Mixer

Texture analysis as a tool to study the kinetics of wet agglomeration processes

Powder flow in vertical high shear mixer granulators

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