Mass‐transfer effects of bubble streams rising near vertical electrodes

Mass‐transfer enhancement by a stream of bubbles rising near a planar, vertical surface is resolved spatially and temporally using a micromosaic electrode. A stream of gas bubbles is generated electrolytically, either at a segment directly below and in the plane of the monitoring electrodes, or at a wire tip that can be positioned inside or outside the mass‐transfer boundary layer. The mass‐transfer enhancement resulting from bubbles rising within the mass‐transfer boundary layer is found to be strong and localized, in agreement with trends predicted by a surface‐renewal model. Mass transfer resulting from bubbles rising outside the boundary layer is found to receive a steady, laminar enhancement, correlating well with predictions from an idealization of the bubble stream entraining a cylinder of liquid.