MASS-TRANSFER AT THE IMPELLERS OF AGITATED VESSELS IN RELATION TO THEIR FLOW-INDUCED CORROSION

To investigate the role of mass transfer in the kinetics of how induce d corrosion of agitated vessels impellers, the rate of mass transfer a t four blade 45 degrees pitched turbine, four blade flat turbine and s ix blade disc turbine was studied using the diffusion controlled disso lution of copper in acidified chromate technique. Variables studied we re impeller rotation speed, physical properties of the solution, impel ler diameter, the presence of baffles in the cylindrical agitated vess el, the presence of suspended solids and the effect of drag reducing p olymers. The blank solution data were correlated in the form: Sh=a Sc- 0.33. Re-b. The values of a and b were found to depend on impeller geo metry. In all cases the presence of baffles in the cylindrical agitate d vessel increases the rate of diffusion controlled corrosion by an am ount ranging from 50% to 115% depending on impeller rotation speed. Th e presence of suspended solids increases the rate of corrosion by an a mount ranging from 7% to 70% depending on impeller rotation speed, sol id concentration and particle size. The presence of Polyox WSR-301 dra g reducing polymer decreases the rate of corrosion by an amount rangin g from 5-49% depending on polymer concentration and impeller rotation speed. The economic worth of using drag reducing polymers in agitated vessels was noted. (C) 1998 Elsevier Science S.A. All rights reserved.