(226a) Vortex Generation with Submerged Baffles

It is often desired in solid-liquid or gas-liquid handling applications utilizing a stirred tank to add a secondary impeller located in the upper region of the vessel and modified baffles to generate a stable vortex at the air-liquid interface to drawdown, wet, and incorporate solids or gas. The vortex for such applications must be stable and of the minimum depth of the upper impeller submergence. The stable generation of a centrally located vortex that reaches impeller about a concentrically mounted shaft in a 0.609 m diameter cylindrical vessel with submerged baffles was investigated using a series of six different types of impellers with varying D/T = 0.3, 0.4, 0.5. The geometric factors of interest were the impeller types, D/T and baffle/impeller-liquid coverage (IBC). The ratio of IBC to impeller diameter (IBC/D) was varied from 1 to a level where a vortex could not be identified.  The impeller horizontal centerline was fixed at the top of the submerged baffle. The minimum vortex depth was correlated with Froude Number, torque/volume, power/volume and tip speed. The aforementioned conditions were observed and classified visually.