Experiments and modelling on electrochemically generated bubbly flows

Abstract

Despite a large demand in the area of electrochemical processes, e.g., the production of sodium chlorate and electrowinning of zinc, the available literature on the flows of micro-bubbles is limited. An experimental investigation of micro-bubbles two-phase flows has been therefore undertaken. The experiments were performed within a vertical pipe (inner diameter 50 mm). An original electrochemical bubble generator has been specially designed for this study. The liquid phase is a salt solution, which inhibits coalescence, so that the electrochemically generated H 2-bubbles exhibit typical diameters about 100 μm, corresponding to a particle Reynolds number about unity. Both the void fraction and the velocity of the micro-bubbles were measured through image analysis. Velocity measurements were also performed using a new type of sensor, based on a mono-modal fiber optics. The void fraction distribution was found to significantly differ from existing results obtained at higher bubble to pipe diameters ratios. The experimental measurements are also compared with numerical simulations based on a 2-D drift flux model. Finally, the experimental results of the paper demonstrate that the use of the Faraday law is questionable as regards its ability to predict the input gas flow rate.