Figure 2 . Sample of processed bubble-image using ImageJ for bubble size measurements. Identified bubbles have contour lines around them.
Bubbles were approximated by ellipsoids in shape, and Equation (2) was used to determine the equivalent diameter (deq ) of a sphere with the same cross-sectional area (Ab ), which was used as the bubble size representative length. Here a is the major bubble axis andAR is the aspect ratio of the bubble. The cross-sectional area, bubble centroid location, and the aspect ratio were calculated for each identified bubble in ImageJ. This equivalent bubble diameter was used in Equation (3) to compute the Sauter mean diameter (d32 ), which is the ratio of the representative bubble volume to the bubble surface area and is a common measure of the average bubble size.