NATURAL-CONVECTION MASS-TRANSFER AT A HORIZONTAL CYLINDER ELECTRODE WITH AN OPPOSED THERMAL BUOYANCY EFFECT

Simultaneous heat and mass transfer at horizontal cylinder electrodes in free convection has been investigated experimentally using the elec trochemical limiting diffusion current technique, in the situation whe re the concentration and thermal buoyancy effects are opposed. The fer ri-ferrocyanide redox system was used for the mass transfer measuremen ts, the electrolyte system being equimolar potassium ferri-ferrocyanid e with 0.5 M NaOH as supporting electrolyte. The chosen concentrations were 0.01, 0.02, 0.05, 0.10 and 0.2M. Two different nickel cylinders of diameter of 33.2 and 21.3mm were used, each 100mm in length. The su rface temperature of the cylinder varied from 20%C (isothermal) to 85% C. Results for the opposed upward and downward convection were correla ted using a combined Grashof number for mass transfer in the range 10( 8)<GR(m)Sc<10(11). The Schlieren technique of Bow visualisation was us ed for observation of the flow structure.