The mixing of cohesive powders

Harnby, N.

doi:10.1016/b978-075063760-2/50026-3

Cited by 50 publications

(31 citation statements)

References 17 publications

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“…The electrostatic force F Ip,e (N) (or Coulomb force) occurs when two solids in rubbing contact charge each other electrostatically. However, the electrostatic forces are several degrees of magnitude smaller than the van der Waals forces (Harnby, 1992) and can therefore be omitted here.…”

Section: Model Developmentmentioning

confidence: 99%

“…The interparticle force is caused by cohesion between individual particles. In the two phase solidair state it results from electrostatic-force bonding and van der Waals -force bonding ( Harnby, 1992). The electrostatic force F Ip,e (N) (or Coulomb force) occurs when two solids in rubbing contact charge each other electrostatically.…”

Section: Model Developmentmentioning

confidence: 99%

“…in the case of wet sediment, are due to liquid-bridge bonding (capillary forces) and adsorbed-layer bonding (adhesion forces). The liquid bridges exert an attractive force between particles once they are formed (Harnby, 1992). When considering the model of Fisher (1926) and the well-known Young-Laplace equation, the capillary force F Ip,c (N) can be written as :…”

Section: Model Developmentmentioning

confidence: 99%

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A parameterisation for the threshold shear velocity to initiate deflation of dry and wet sediment

2004

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A new parameterisation for the threshold shear velocity to initiate deflation of dry and wet particles is presented. It is based on the balance of moments acting on particles at the instant of particle motion. The model hence includes a term for the aerodynamic forces, including the drag force, the lift force and the aerodynamic moment force, and a term for the interparticle forces. The effect of gravitation is incorporated in both terms. Rather than using an implicit function for the effect of the aerodynamic forces as reported earlier in literature, a constant aerodynamic coefficient was introduced. From consideration of the van der Waals force between two particles, it was further shown that the effect of the interparticle cohesion force between two dry particles on the deflation threshold should be inversely proportional to the particle diameter squared. The interparticle force was further extended to include wet bonding forces. The latter were considered as the sum of capillary forces and adhesive forces. A model that expresses the capillary force as a function of particle diameter squared and the inverse of capillary potential was deduced from consideration of the well-known model of Fisher and the Young-Laplace equation. The adhesive force was assumed to be equal to tensile strength, and a function which is proportional to particle diameter squared and the inverse of the potential due to adhesive forces was derived. By combining the capillary force model and the adhesive force model, the interparticle force due to wet bonding was simplified and written as a function of particle diameter squared and the inverse of matric potential. The latter was loglinearly related to the gravimetric moisture content, a relationship that is valid in the low-moisture content range that is important in the light of deflation of sediment by wind. By introducing a correction to force the relationship to converge to zero moisture content at oven dryness, the matric potential-moisture content relationship contained only one unknown model parameter, viz. moisture content at -1.5 MPa. Working out the model led to a rather simple parameterisation containing only three coefficients. Two parameters were incorporated in the term that applies to dry sediment and were determined by using experimental data as reported by Iversen and White [1982. Sedimentology 29, 111-119 ]. The third parameter for the wet-sediment part of the model was determined from wind-tunnel experiments on prewetted sand and sandy loam aggregates. The model was validated using data from wind-tunnel experiments on the same but dry sediment, and on data obtained from simulations with the model of Chepil [1956. Soil Sci. Soc. Am. Proc. 20, 288-292]. The experiments showed that soil aggregates should be treated as individual particles with a density equal to their bulk density. Furthermore, it was shown that the surface had to dry to a moisture content of about 75% of the moisture content at -1.5 MPa before deflation became sustained. The threshold shear veloci...

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Section: Model Developmentmentioning

confidence: 99%

Section: Model Developmentmentioning

confidence: 99%

Section: Model Developmentmentioning

confidence: 99%

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A parameterisation for the threshold shear velocity to initiate deflation of dry and wet sediment

2004

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“…The inclusion of spouting jets of air, in addition to the main supply of fluidizing air, can enhance the mixing [1-3, 6-8, [16][17][18][19][20][21][22].…”

Section: Fluidized Bed Mixersmentioning

confidence: 99%

Mixing, Emulsification, and Size Reduction

Brennan¹

2011

Food Processing Handbook

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“…Thus, these factors influence the lung dose of inhalation products. In the mixing of cohesive powder, coarse particles act as nuclei, which are coated with a single layer of fine particles (17). If fine particles are in excess, it is assumed that they would agglomerate in a similar way around a nucleus of a fine particle.…”

Section: Introductionmentioning

confidence: 99%

Dry Powder Inhalers: Study of the Parameters Influencing Adhesion and Dispersion of Fluticasone Propionate

Thi

Robins³

et al. 2012

AAPS PharmSciTech

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Abstract. Interactions between particles are dependent on the physicochemical characteristics of the interacting particles but it is also important to consider the manufacturing process. Blending active pharmaceutical ingredient (API) with carrier is a critical stage that determines the blend homogeneity and is the first step towards obtaining the final quality of the powder blend. The aim of this work was to study parameters that influence the interactions between API and carrier in adhesive mixtures used in DPI and their effect on API dispersion. The study was done with fluticasone propionate blended with lactose 'Lactohale 200'. The study was based on the influence of the operating conditions (speed, mixing time, resting steps during mixing), the size of the carrier and the storage conditions on the blend properties and on the API dispersion. The quality of the blends was examined by analysing the API content uniformity. Adhesion characteristics were evaluated by submitting mixtures to a sieving action by air depression with the Alpine air-jet sieve. Aerodynamic evaluation of fine particle fraction (FPF) was obtained using a Twin Stage Impinger; the FPF being defined as the mass percentage of API below 6.4 μm. For good dispersion and therefore good homogeneity of the API in the carrier particles, speed and powder blending time have to be sufficient, but not too long to prevent the appearance of static electricity, which is not favourable to homogeneity and stability. The FPF increases with the decrease in the carrier size. The storage conditions have also to be taken into consideration. Higher humidity favours the adhesion of API on the carrier and decreases the FPF.

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The mixing of cohesive powders

Cited by 50 publications

References 17 publications

A parameterisation for the threshold shear velocity to initiate deflation of dry and wet sediment

A parameterisation for the threshold shear velocity to initiate deflation of dry and wet sediment

Mixing, Emulsification, and Size Reduction

Dry Powder Inhalers: Study of the Parameters Influencing Adhesion and Dispersion of Fluticasone Propionate

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