Laminar and slurry blending characteristics of a dual shaft impeller system

The hydrodynamic performance of a dual shaft mixer consisting of a low-speed, wallscraping, Paravisc-type impeller and an off-centered, high-speed, high-shear Deflo disperser have been experimentally investigated in the case of dispersing fine solids in a viscous Newtonian continuous phase. The experiments were restricted to the laminar regime and made use of two different types of solid particles namely: calcium carbonate and glass beads, at a constant concentration of 10 wt%. Glucose solutions were used as the Newtonian continuous phases. The single phase hydrodynamic characterization showed that the Paravisc impeller power consumption can be significantly affected by the rotation of the Deflo disperser, revealing the importance of the turbine on the overall mixing performance. Mixing time measurements showed that the Paravisc effectively controls the bulk flow movement but requires the presence of a baffle, or a second shaft acting as such, in order to output effective mixing performance. This observation is also valid in solids dispersion where the Paravisc impeller exerts a major influence on the time required to achieve a stable dispersion. The homogenization efficiency tests performed showed the ability of the Deflo disperser to efficiently break up the agglomerates in the vessel.