MASS-TRANSFER STUDY OF THE ELECTROPOLISHING OF VERTICAL CYLINDERS WITH ACTIVE ENDS UNDER NATURAL-CONVECTION CONDITIONS

Rates of electropolishing of vertical copper cylinders with active end s in H3PO4 were studied by measuring the limiting current under natura l convection, Variables studied were H3PO4 concentration, cylinder dia meter and aspect ratio. The rate of polishing of the whole cylinder wa s represented by the mass transfer equation Sh = 0.33(Sc Gr)(0.32) for the range 1.17 x 10(10) < Sc Gr < 5.11 x 10(11). Rates of mass transf er were measured also at vertical cylinder with insulated ends, and th e upward facing surface (disc). Data for the vertical cylindrical surf ace were represented for the range 8.75 x 10(9) < Sc Gr < 1.1 x 10(12) by the equation Sh = 1.206(Sc Gr)(0.255) while data at the upward fac ing disc were correlated for the range 0.11 x 10(10) < Sc Gr < 46 x 10 (10) by the equation Sh = 0.17SC(0.396)(SC Gr)(0.146) A comparison bet ween the measured rate of mass transfer at the whole cylinder and the value calculated by adding the rates of mass transfer at the separate surfaces of the cylinder shows that the measured value deviates from t he calculated value, the degree of deviation increases with increasing Sc x Gr, Deviation was attributed to flow interaction at the differen t cylinder surfaces.