A mixing performance of an inner baffle was investigated in shear thinning fluid. The inner baffle was placed with a clearance between baffle and vessel wall. A traditional two-bladed paddle impeller was used. Four planar baffles were vertically placed in two ways: 1) standard baffle condition 2) inner baffle condition. The standard baffle condition was that the baffle was placed on the mixing vessel wall. A mixing pattern was visualized by decolorization method based on an oxidation-reduction reaction with sodium thiosulfate and iodine. Flow field for shear thinning fluid in mixing vessel was measured by particle image velocimetry and was shown as stream line. A pair of isolated mixing regions (IMR) like doughnut-ring formed above and below the impeller under standard baffle condition. However, IMR dissipated under inner baffle condition. As a result, a mixing time under the inner baffle condition was drastically decreased. This study suggested that inner baffle promoted mixing in shear thinning fluid.
The mixing performance of baffles placed with a clearance between them and the mixing vessel wall was investigated in a shear-thinning fluid, and decolorization experiments were conducted to observe the mixing pattern under no-baffle, standard baffle, and inner-baffle conditions. Velocity fields were obtained by particle image velocimetry to clarify the mixing mechanism in the fluid. No isolated mixing region was seen under the inner-baffle condition, and this condition promoted homogeneous mixing. The velocity profile clarified that the inner baffle prevented secondary circulation flow from forming an isolated mixing region and, thus, promoted homogeneous mixing in the fluid. An inner baffle with a small impeller can obtain homogeneous mixing in shear-thinning fluids.
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