Froude number granulation

Dimensionless numbers, such as Reynolds and Froude numbers, are frequently used to describe mixing processes. Chemical engineers are routinely concerned with problems of water-air or fluid mixing in vessels equipped with turbine stirrers where scale-up factors can be up to 1 70 (3). This approach has been applied to pharmaceutical granulation since the early work of Hans Leuenberger in 1982 (4). 

Another equipment parameter is the Froude number (Fr), a dimensionless number calculated as shown in Eq. (2), where v represents the impeller speed (rpms) and r is the radius of the granulator bowl. 

Based on the machine design parameters, high-shear granulation equipment of the same type will usually vary less in tip speed, Froude number, and RSV upon scale-up in equipment size. The differences in Froude number and RSV among high-shear mixers of different types are less as the size of the equipment increases. Therefore, development and scale-up are easier if the same type of high-shear equipment is used. 

In a seminal and elegant work published in 1993, Horsthuis et al. from Organon in The Netherlands have studied granulation process in Oral mixers of 10, 75, and 300 L size. Comparing relative swept volume, blade tip speed and Froude numbers with respect to end-point determination (as expressed by the time after which there is no detectable change in particle size), they have concluded that only constant Froude numbers result in a comparable end-point. 

Froude Number has been described for powder blending and was suggested as a criterion for dynamic similarity and a scale-up parameter in wet granulation. The mechanics of the phenomenon was described as interplay of the centrifugal force (pushing the particles against the mixer wall) and the centripetal force produced by the wall, creating a compaction zone. ... 

Froude number, potentially providing a scale-up rule for mixer granulation. 

Froude number (Fr) is the ratio of the centrifugal acceleration to the gravitation constant (g). It can be used as a criterion for dynamic similarity of granulators ... 

One practical approach during scale-up is to keep the processes dynamically similar, which is defined by the same dimensionless numbers for the two different sizes of granulators. Therefore, dimensionless numbers such as Froude number can be used for scale-up. 

Dimensionless numbers such as Froude number can also be used to design and select high-shear granulators of different scales. It is therefore necessary to characterize and compare high-shear granulators of different types and sizes by the range of... 

The matching Froude numbers for different size granulators provide the possibility of linear scale-up. However, some precautions are still needed for the geometric dissimilarity of mixing bowl vessels, and the shape of the impellers in the granulators of different types and scales. 

During scale-up, after selecting the granulator with matching Froude number and similarly shaped impeller blades, the granulation end point can be determined by any one of the techniques described earlier. A new approach for scale-up based on the use of power consumption, as the granulation end-point determination, is shown below. 

Dimensionless numbers most commonly used to describe the wet granulation process are Newton, Froude, and Reynolds ... 

Scale-up in fixed bowl mixer-granulators has been studied by Rowe and Cliffs group using the classical dimensionless numbers of Newton (power), Reynolds, and Froude to predict the end-point in geometrically similar high-shear Fielder PMA 25, 100, and 600 L machines. 

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