Search tips
Search criteria 


Logo of aapspharmspringer.comThis journalToc AlertsSubmit OnlineOpen Choice
AAPS PharmSciTech. Sep 2012; 13(3): 928–933.
Published online Jun 26, 2012. doi:  10.1208/s12249-012-9818-z
PMCID: PMC3429663
The Stokes Number Approach to Support Scale-Up and Technology Transfer of a Mixing Process
Tofan A. Willemsz, Ricardo Hooijmaijers, Carina M. Rubingh, Henderik W. Frijlink, Herman Vromans, and Kees van der Voort Maarschalkcorresponding author
Department of Pharmaceutical Technology and Biopharmacy, University of Groningen, A. Deusinglaan 1, 9713 AV Groningen, The Netherlands
Pharmaceutical Sciences and Clinical Supply, Merck MSD, PO Box 20, 5340 BH Oss, The Netherlands
Quality of Life, TNO, PO Box 360, 3700 AJ Zeist, The Netherlands
Department of Pharmaceutics, Utrecht Institute for Pharmaceutical Sciences (UIPS) Utrecht University, PO Box 80082, 3508 TB Utrecht, The Netherlands
Competence Center Powders and Formulations, Purac Biochem, PO Box 21, 4200 AA Gorinchem, The Netherlands
Kees van der Voort Maarschalk, Phone: +31-412-662342, Fax: +31-412-662617, tofan.willemsz/at/
corresponding authorCorresponding author.
Received February 8, 2012; Accepted June 8, 2012.
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