Effect of gas evolution on dispersion in an electrochemical reactor

Abstract

Gas evolution at electrodes is encountered in many electrochemical processes, and the resulting gas bubbles affect mixing or dispersion in the neighbouring liquid. Experiments were conducted to study the effect of electrogenerated gas bubbles on dispersion in the fluid close to wall in a parallel-plate electrochemical reactor. Platinum microelectrodes and copper electrodes were used to generate gas (hydrogen or oxygen depending on polarity) bubbles and to measure dispersion, respectively. Estimated void fraction of gas bubbles was less than 0.01. Response curves were modelled using the axially dispersed plug flow model. Results obtained indicate that mean residence time of marked material (i.e. fluid close to wall) is almost unaffected by gas bubbles. Dispersion coefficient, however, increases with gas evolution at low liquid flow rates (say, for Reynolds number less than 100); but it is unaffected at higher flow rates. The effect of hydrogen and oxygen bubbles on dispersion under the range of conditions studied, appears to be similar. © 1993 Chapman & Hall.