Scaling up of silverson rotor–stator mixers

In-line rotor–stator mixers are widely applied in industry for the formulation of emulsion products; however, the current understanding of breakage/coalescence in such devices is limited. In this study the effect of rotor speed, flow rate and dispersed phase viscosity on drop size distributions in an industrial and in a lab scale in-line Silverson rotor–stator mixer were investigated. Silicone oils with viscosities of 9.4 and 339 mPa s at 1 wt.% were emulsified in surfactant solution. Sauter mean diameters were correlated with various parameters and it has been found that Weber number is the most appropriate scaling parameter. Energy dissipation rate is a marginally poorer scaling parameter and this term requires prior knowledge of the experimentally determined power constants. Based on these observations it seems sensible to use Weber number as the preferred scaling-up parameter.