A study was made of the influence of process parameters on the mass-transfer coefficient in a flow-through cell with a cascade of rotating drums partially filled with conductive particles ( called the 'vertically moving particle bed'). Copper deposition from an acidic sodium sulphate solution was used as the model reaction. To evaluate the experimental data a macrohomogeneous mathematical model of potential and current density distribution inside the cell was developed. The electrolyte flow distribution between the empty space above the particle bed and through the bed was evaluated. On the basis of these results the following correlation is proposed:Sh = 1.09/epsilon Re-p(1/3) Sc-1/3 + 52.8 Re-r/ 2498 + Re-r {1 - exp [-125(1.04 x 10(-6)Re(r) + Re-p)]}where the first term corresponds to the packed bed electrode and the second term represents the contribution of bed rotation. It is valid for bed porosity of 45%, cathode drum rotation rates between 0.047 and 0.120 Hz (i.e., 2.8 to 7.2 rpm) and a Re-p range of 0.003 to 0.013.