Scalar mixing measurements in batch operated stirred tanks

An LIF technique was used to obtain unobtrusive measurements of scalar concentration as a function of time and mixing times in a fully baffled batch operated mixing vessel agitated by five forms of impeller (Rushton, ‘bucket’, six bladed 45°-and 60°-pitched blade, hyperboloid). The mixing time was comparable to the time required for the dye/scalar to be transported from the top of the vessel to the bottom part plus the time required for a further two rotations of the bulk flow in the circumferential direction. At constant power input the mixing times for similar impellers were similar, although different for different types. On a utilise une technique LIF afin d'obtenir des mesures non intrusives de concentration scalaire en fonction du temps et des temps de melange dans une cuve agitee munie de contrepales pour cinq types de turbines (Rushton, “a abues”, a 6 pales inclinees a 45° et 60°, hyperboloides) en regime discontinu. Le temps de melange est comparable au temps requis pour le transport du colorant/scalaire depuis le sommet du reservoir jusqu'a sa base plus le temps requis pour encore deux rotations du coeur de l'ecoulement dans la direction circonferentielle. A puissance constante, les temps de melange pour des turbines semblables sont similaires, mais ils different lorsque les turbines sont de differents types.