Measurement and Analysis of Gas Bubbles near a Reference Electrode in Aqueous Solutions

Bubble size distributions (BSDs) near a reference electrode (RE) in aqueous glycerol solutions of an electrolyte NaCl have been investigated under various gas superficial velocities (Us). BSD and voltage reading of the solution were measured by using a highspeed digital camera and a pH/voltage meter, respectively. The results show that bubble size (b) increases with liquid viscosity ((mu)c) and Us. Self-similarity is seen and can be described by the log-normal form of the continuous number frequency distribution. The result shows that b controls the voltage reading in each solution. As b increases, the voltage increases because of gas bubbles interrupting their electrolyte paths in the solutions. An analysis of bubble rising velocity reveals that Stokesʹ Law should be used cautiously to describe the system. The fundamental equation for bubble formation was developed via Newtonʹs second law of motion and shown to be the function of three dimensionless groups-Weber number, Bond number, and Capillary number. After linking an electrochemical principle in the practical application, the result indicates that the critical bubble size is ~177 (mu)m. Further analysis suggests that there may be 3 000 to 70 000 bubbles generated on the anode surface depending on the size of initial bubbles and provides the potential cause of the efficiency drop observed in the practical application.