Rates of mass transfer at rotating single horizontal screen disc and rotating stacks of closely packed and separated screens were studied by measuring the limiting current for the cathodic reduction of ferricyanide ions. Variables studied were screen rotation speed, mesh number of the screen, physical properties of the solution, number of screens per stack, screen separation and the effect of superimposed axial flow. Mass transfer data at single rotating screen disk were correlated by the following equation which is based on the surface renewal model J = 0.26 Re-0.5 (r/d(w))(0.5). Mass transfer rates at rotating closely packed screen bed were found to decrease below the single screen value by an amount ranging from 20 to 43.6% depending on rotation speed, mesh number and number of screens per bed. Superimposed axial flow was found to increase the rate of mass transfer at rotating screens especially at Re-f>1095. Implications of the present results for the design of high space time yield electrochemical reactors and catalytic reactors were noted. (C) 2000 Elsevier Science S.A. All rights reserved.