Mass transfer by free convection at horizontal electrodes

Limiting currents were measured in an unstirred cell at horizontal cathodes facing upward. Electrolyte composition ranged from 0·01 to 0·7 M CuSO4 in 1·5 M H2SO4. Cathode sizes varied from 0.1–30 by 10 cm, and the free height above the electrode from 1–16 cm. Limiting currents for deposition of copper ranged from 0·68–129 mA/cm2. For electrode width larger than 20 mm the data is well represented by the general correlation Nu′ = 0.19 (Sc. Gr)13, where Nu′, Sc, and Gr are the Nusselt number for mass transfer, the Schmidt, and Grashof numbers, respectively. The experimental range used in the correlation included 108 < (Sc. Gr) < 1·4 × 1012 The results indicate that the boundary layer is turbulent, as it is in the case of the analogous heat-transfer model.