Laminar Mixing in Eccentric Stirred Tank with Different Bottom

Abstract

Effect of eccentrically located position of impeller on mixing time was investigated in agitated vessels of different bottom shapes. The impellers used were a 4-bladed propeller and a 6-bladed flat paddle, which were commonly used in process industries, and the bottom shapes tested were a cone-fillet, a fully profiled and an ellipsoid bottom in addition to a flat bottom. The effect of off-bottom clearance of impeller on mixing time was also investigated at optimum eccentric locations for both impellers. For propeller, mixing times for all eccentric location covered in this work (e/R = 0.25–0.50, e: distance from shaft to center line of tank, R: radius of tank) became short drastically compared to those for centrally located for all bottom shapes and there was no significant effect of bottom shapes on mixing time. On the other hand, for flat paddle, mixing times were decreased proportionally with an increase in e/R. At optimum eccentric locations, those are e/R = 0.33 for propeller and 0.50 for flat paddle, the mixing times for propeller decrease drastically and then increase slightly with an increase in off-bottom clearance for all bottom shape and those for flat paddle decrease almost proportionally with an increase in off-bottom clearance but differed more or less according to the bottom shapes.