Prediction of Mixing Pattern by Using Power Number Diagram in Baffled and Unbaffled MixingVessels

摘要

Mixing patterns generated in stirred vessels for a wide range of Reynolds numbers were observedusing a decolorization method based on the reaction between sodium thiosulfate and iodine. Arelationship was established between the power number diagram (N_P-Re diagram) and the shape ofthe isolated zone was observed. At low Reynolds numbers (laminar regime), the isolated zoneresembled a doughnut ring, while a cylindrically rotating zone isolated at high Reynolds numbers(turbulent regime). Even with a small change in Reynolds number, the doughnut-ring-shaped isolatedzone suddenly changed to a cylindrically rotating zone in an unbaffled vessel. The cylindricallyrotating zone was not observed in baffled vessels at high Reynolds numbers. The clearance betweenthe propeller impeller and the vessel bottom brought about a change in the mixing patterns, althoughthe power consumption the remained constant.