Mass transfer and free convection associated with electrodeposition at long narrow upward facing tracks

This paper describes an investigation of free convection and mass transfer at narrow upfacing tracks 100 mm long, associated with copper deposition from a sulphate/sulphuric acid bath. The electrode width was varied from 0.8 to 7.5 mm, and the copper sulphate concentration from 0.01 to 0.28 M thus allowing a broad range of Rayleigh number to be investigated. The onset of free convection was identified by measurement of the transient current and use of an interferometric (schlieren) technique. The critical time corresponding to the onset of free convection was shown to depend on the technique used. After one or two minutes the current reached a steady value for high Ra and exhibited regular oscillations of appreciable amplitude for Ra below 10(6). Determination of mass transfer rates from the steady state currents gave a dependence of Sherwood number on Ra-033 for Ra over 2 x 0(5), indicating turbulent natural convection. The low value for the transitional Ra is attributable to the peculiar aspect ratios of the electrodes. (C) 2000 Elsevier Science Ltd. All rights reserved.