FREE CONVECTIVE MASS-TRANSFER AT UP-POINTING PYRAMIDAL ELECTRODES

A limiting current technique was used for the measurement of the free convective mass transfer rate at entire upward pointing pyramids. The mass transfer rate at a single inclined pyramidal surface was correlat ed by the equation: Sh(L) = 0.828(Ra-L,Ra-theta)(0.25) for the Ra-L,Ra -theta range 1 x 10(7) to 2 x 10(11). It was found that the mass trans fer rate for the combination of all inclined faces was lower than that for the single inclined surface. The down-pointing horizontal base su rface has a strong influence on the total mass transfer rate for entir e upward pointing pyramids. The experimental total mass transfer data were correlated using a method which includes an interference factor t aking account of the fact that the three inclined triangular faces are exposed to fluid which has already been depleted in copper ions as it flows upward from the base. The dependence of the interference factor on the aspect ratio of the pyramid (L/b) was not so strong as for ver tical cylinders or down-pointing pyramids. (C) 1997 Elsevier Science L td.