Analysis of mixed natural and forced convection copper deposition below the limiting current

Effective mass transfer boundary-layer thicknesses at a segmented vertical plate cathode were measured experimentally using the potential relaxation technique. Copper deposition at currents near and below the diffusion limiting current was investigated for assisting and opposing mixed natural and forced convection stirring. Mass transfer to the lower region of the plate was controlled by pure forced convection during assisting flow and laminar natural convection during opposing flow. At the upper portion of the plate, pure natural convection regulated the boundary-layer thickness during assisting flow whereas laminar forced convection dominated for the opposing flow case. Turbulent mass transfer was observed in the middle section of the cathode during opposing flow. The results suggest that turbulence was generated by flow instabilities and boundary-layer separation, which is analogous to that reported in opposing flow heat transfer studies. For the case of assisting mixed convection copper deposition, the following local Sherwood number correlation was generated from experimentally measured boundary-layer thicknesses, Sh^2.8 _M = Sh³ _N + Sh³ _F.