Flow Characteristics In Transition Region Of Multi-impeller In A Stirred Tank

Mixing is widely used in Chemical production process.Multi-impeller is required when the ritio of height to diameter is large.Early studies considered that the power of multi-impeller is the accumulation of single-impeller,which has been causing wastage in industry.In polymerization and other chemical production processes,with the progress of the reaction,the viscosity of materials often increases,resulting in the transformation of flow pattern from the turbulent flow into the transition flow.At present,the research on multi-impeller is mainly concentrated in turbulent flow,and the studies on transition region is less.Therefore,it is of great significance for industry to study the flow characteristics in the transition region of multi-impeller.In this paper,research is studied by two different ways:experiment and Computational Fluid Dynamics.The power characteristics,flow field and mixing time of the stirred tank(T=476mm)with CBY impeller(D=190mm)are studied under different impeller spacing and agitation Reynolds number.The conclusion is as follows:1.With the increase of the Reynolds number,the power number ratio of the double CB Y impellers in the transition region first increases and then decreases.In the near-laminar region and near-turbulent region,the power number increases with the increase of impeller spacing,but varies in the middle rigion depending on the Renolds number.Power number ritio is decreased significantly at L=0.25D when Re>842.2.With the increase of impeller spacing,the power number of lower CBY impeller increases,and that of upper impeller changes depending on Reynoldsc number.When Re>842,it is obviously that the power number of upper impeller at L=0.75D increases,while decreases at L=1.25D.3.There are three kinds of flow field in transition zone of double CBY impeller:parallel flow,merging flow and diverging flow.With the increase of the Reynolds number and the decrease of impeller spacing,the flow field of the double-layer CBY impeller tends to be parallel flow-diverging flow-merging flow.4.The mixing time will be shortened when the impeller spacing is reduced in the similar flow field.