MASS-TRANSPORT ENHANCEMENT BY RISING BUBBLE CURTAINS

Mass-transport enhancement by rising single and multiple bubble stream s was monitored on a vertical electrode incorporating a mosaic of 100 x 100 mum sensing elements. Limiting current measurements of the reduc tion of ferric to ferrous sulfate revealed the presence of two distinc t mechanisms: surface renewal is effective within a swath of five bubb le diameters, while macroscopic laminar flows induced by rising bubble s contribute weaker enhancement over a wider path. Enhancement caused by a sheath of multiple side-by-side bubble streams can be well repres ented by the linear superposition of the effect of single streams. Gen erally, at equivalent volumetric rates, small bubbles are more effecti ve than larger ones in reducing mass-transfer resistance to the underl ying surface.