Measurement of bubble shape and size in bubbly flow structure for stagnant and pulsating liquid flow using an undivided electrochlorination cell and Telecentric Direct Image Method

This study presents the measurement of shape and diameter of bubbles in different regions of the bubbly flow structure at the cathode for stagnant and pulsating liquid flow in a single undivided electrochlorination cell. The cell is filled with a dilute sodium chloride electrolyte solution with a concentration of 30 g/L, and operated at a current density of 18.75 mA/cm2, and stagnant liquid flow, or pulsating liquid flow with a pulsation period of 3.5 s and rate of 760 mL/h. Measurements are conducted using a Telecentric Direct Image Method for acquiring images of the bubbles, and processing is done in MATLAB and NI Vision in LabVIEW to determine shape and diameter of the bubbles. Three bubble regions are observed; adherence, bubble diffusion and bulk region. For stagnant liquid flow the mean bubble diameter increases from 30 to 60 μm going from the adherence region to the bulk region, which is supported by an increase in fraction of total gas volume constituted by large bubbles. For pulsating liquid flow the mean bubble diameter is observed to remain constant around 35 μm when moving across the bubbly flow structure, which likewise is supported by the fraction of total gas volume investigations. Hence, showing horizontal displacement of the three bubble regions with the pulsating liquid flow.