Scale-Up of High-Shear Mixer Granulators

Effective scale-up of mixer granulators is more difficult than in fluidized beds. There are several reasons for this  

In this section, we will focus mainly on vertical shaft mixer, e.g.. Fielder, Diosna designs. Some of the suggested approaches may be used with caution for other mixer designs. 

For a simple vertical mixer design, the key dimensions are the impeller diameter D, which is usually equal to the bowl diameter, the chopper diameter Dc, and the fill height H. The dimensionless groups that need to be held constant for geometric similarity are 

In addition, the shape and positioning of the impeller and chopper should be the same on scale-up. Unfortunately, manufacturers do not always adhere to these 

Relative All height is also often varied with scale. This often reflects the small-size batches required for early-stage clinical trials and the desire to maximize production rate (by maximizing batch size) at full scale. Varying relative fill height is very dangerous, as it can have a major impact on powder flow patterns. 

---