FREE CONVECTIVE MASS-TRANSFER AT DOWN-POINTING PYRAMIDAL ELECTRODES

A limiting current technique was used for the measurement of the free convective mass transfer rate at entire down-pointing pyramids and als o at the individual faces of the pyramids. The cathodic deposition of Cu2+ ions at electrodes of varying geometries was used as the mass tra nsfer process, the supporting electrolyte being sulphuric acid. The ma ss transfer rate at a single inclined pyramidal surface was correlated by the equation Sh(L) = 0.78(Ra-L,Ra-theta)(0.25) for the Ra-L,Ra-the ta range 9.3 x 10(6) to 2 x 10(11). The mass transfer data for the ent ire pyramid were correlated using a method which includes an interfere nce factor taking account of the fact that the upward-facing horizonta l surface is exposed to fluid which has already been depleted in coppe r ions. The dependence of the interference factor on the aspect ratio of the pyramid (L/b) was established.