Free convective mass transfer at circular thin disk electrodes with varying inclination

Abstract

The electrochemical limiting diffusion current technique was used to evaluate free convective mass transfer rates at free-standing circular disk electrodes of varying inclination and diameter. The electrochemical system used was copper deposition from acidified cupric sulphate solution. Experiments were carried with the single faces active and also with both faces simultaneously active. A Toepler–Schlieren system was used to photovisualise the ascending convection streams in order to obtain flow pattern information. For the upward-facing surface, the flow separates at a certain distance from the leading edge of the inclined disk, whereas the flow on the downward-facing surface always stays attached. The data correlations for the doubled disks show an exponent in the Sh– Ra correlation ranging from 0.25 (vertical case), indicating laminar flow, to 0.294 (horizontal case), indicating a mixed effect of turbulent separated flow on the upward-facing side and attached flow on the downward-facing surface. A universal correlation Sh d = f A ( Ra d ) f B was obtained for disk diameters d from 5 to 80 mm and inclination angle from 0° to 90° (from the vertical) where f A and f B are functions of inclination.