1. Introduction
It is well-accepted that local shear, elongation and necking are
very important aspects of drop formation as are the physical properties
of the fluids involved. Hence a successful design depends
on developing amechanistic understanding of how the equipment
selection, process strategy and material properties interact to affect
the resulting microstructure (e.g. particle size) and hence the performance
of the products. Typically two approaches are adopted:
• Scale-up at geometric similarity and constant tip speed.
• Scale-up at equal specific power input.
Scale-up on the basis of geometric similarity and constant tip
speed assumes that the relevant shear that produces the limiting
drop size occurs in the agitator region where the velocity gradients
are the steepest. These are assumed to scale with the peripheral
velocity of the impeller and the approach generally works
∗ Corresponding