The Art Of High Shear Mixing

The high-shear rotor/stator mixer (HSM), once relegated to a relatively narrow niche of mixing applications, has become a mainstay in many applications in the chemical process industries (CPI). The ability to apply intense shear and shorten mixing cycles gives these mixers broad appeal for applications that require immiscible fluids to be formulated into emulsions, or agglomerated powders to be dispersed into a liquid medium. Especially during the last decade, the emergence of new variations on the original rotor/stator mixer concept has extended the HSM's usefulness to more diverse applications. For instance, conventional HSMs in both top-entering batch configurations and inline versions, are widely used today for high-intensity mixing, dispersion, disintegration, emulsification and homogenization.

Applications range from dispersions involving gums, pigments, fumed silica, calcium carbonate and active drugs, to emulsions such as cosmetic creams, lotions, and flavors. However, despite the growing popularity of HSMs in many industries, they are still widely misunderstood. Industry-based and university researchers have focused mainly on working out the dynamics of conventional low-shear mixing technologies, such as axialand radial-flow turbines. With only a few notable exceptions, high-shear mixing has been largely overlooked in terms of fundamental research to unlock its mysteries and help users to better predict mixing outcomes, particularly during scale-up.