Drop size distribution monitoring of oil-in-water emulsions in SMX+ static mixers: Effect of operating and geometrical conditions

Static mixers provide enhanced mixing via a motionless element inside a rigid pipe, and are widely used for continuous mixing and blending in industry. This study focuses on the emulsification of a silicon oil-in-water system stabilized by a surfactant through SMX+® static mixers involving no mass transfer between the two phases. The experiments covered a large domain of dispersed fraction from dilute conditions (5 %vol.) up to concentrated ones (60 %vol.) close to phase inversion and three different viscosities from 20 to 350 mPa s with transitional or turbulent flow regimes. The number of static mixers was studied until a constant drop size distribution monitored at line with a video probe was obtained. With the considered flow rates, only the five first SMX+ elements were necessary to achieve a complete drop breakup and coalescence equilibrium, the following ones only causing a supplementary pressure drop. The influence of the number of SMX+ and energy dissipation rate was found to be of first order compared to the volume fraction or viscosity of the dispersed phase. According to the large amount of data, it was possible to establish a new form of a Middleman correlation dedicated to this type of mixer of new generation. The formula takes into account the number of static mixers besides other hydrodynamic and physicochemical parameters.