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AAPS PharmSciTech. 2012 September; 13(3): 928–933.
Published online 2012 June 26. doi:  10.1208/s12249-012-9818-z
PMCID: PMC3429663

The Stokes Number Approach to Support Scale-Up and Technology Transfer of a Mixing Process


Transferring processes between different scales and types of mixers is a common operation in industry. Challenges within this operation include the existence of considerable differences in blending conditions between mixer scales and types. Obtaining the correct blending conditions is crucial for the ability to break up agglomerates in order to achieve the desired blend uniformity. Agglomerate break up is often an abrasion process. In this study, the abrasion rate potential of agglomerates is described by the Stokes abrasion (StAbr) number of the system. The StAbr number equals the ratio between the kinetic energy density of the moving powder bed and the work of fracture of the agglomerate. In this study, the StAbr approach demonstrates to be a useful tool to predict the abrasion of agglomerates during blending when technology is transferred between mixer scales/types. Applying the StAbr approach revealed a transition point between parameters that determined agglomerate abrasion. This study gave evidence that (1) below this transition point, agglomerate abrasion is determined by a combination of impeller effects and by the kinetic energy density of the powder blend, whereas (2) above this transition point, agglomerate abrasion is mainly determined by the kinetic energy density of the powder blend.

Key words: dry mixing, scale-up, stokes number

Articles from AAPS PharmSciTech are provided here courtesy of American Association of Pharmaceutical Scientists