Enhancement of Mass Transfer by Air Bubbling in Electrodialyzer Compartment

Abstract

In this study, a bubble cleaning-type electro dialyzer was developed. In this device, air bubbles act as turbulence promoter and cleaner for membrane fouling. The mass transfer promoting effects of bubbles was investigated with rectangular channels having a narrow clearance of 15 mm, which corresponds to compartments of an electrodialyzer. Mass transfer coefficients k_L, were obtained by means of an electrochemical reaction of the redox system.
It was confirmed that bubble agitation is highly effective on the grounds that k_L, is increased by five to ten times by bubbling, and the effect of bubbling extends fairly uniformly along the channel. In comparison with the effect of net-type spacers used in the conventional electrodialyzer, bubbles exhibited equal ability at low flow rate of solution and at low pressure drop. From these results, it becomes clear that the structure of the bubble cleaning-type electrodialyzer is simplified and that once-through treatment can be realized with this device.
Furthermore, experimental formulas which express the relation between J_D factor of mass transfer and friction factor were obtained under the conditions of bubble agitation and spacer insertion. A correlation between k_L and bubble rising velocity was also determined.