Effect of drag reducing polymers and impeller geometry on the rate of mass and heat transfer at the wall of a cylindrical stirred tank reactor in relation to catalytic reactor design

Abstract

The effect of impeller geometry on the rate of liquid-solid mass transfer at the wall of the stirred tank reactor was studied by measuring the rate of the diffusion-controlled disintegration of copper in acidified dichromate. Factors examined were rotation speed of impeller and its geometry, drag reducing polymer concentration, solution physical properties and baffles effect. The mass transfer data in the blank solution were correlated by dimensionless correlations. Radial flow impellers produced higher rates of mass transfer than axial flow impellers under the same conditions. For a given set of conditions the presence of baffles was found to increase the rate of mass transfer more than unbaffled reactors. Drag reducing polymer was found to decrease the mass transfer rate by an amount ranging from 3.5 to 38.5% depending on rotation speed of impeller, polymer concentration and impeller geometry. Implication of the present results for stirred tank biochemical reactors which use drag reducing polymer to control solution viscosity and decrease the shear stress between the moving solution and the vessel wall as to protect immobilized enzyme or cells fixed to the wall against mechanical damage were discussed. The present results would help in evaluating the financial possibility of utilizing drag reducing polymers in working biochemical stirred tank reactors. Keywords: Drag reducing polymer, Mass transfer, Heat transfer, Diffusion controlled reactor, Impeller geometry, Mechanical power