Results and discussion
The examples of MBs analysis are shown in Figure. 3, the difference in diameter of bubbles in the focal length range can be seen, and bubbles range in diameter from about 10 μm to 200 μm. Throughout the whole process of analysis of the video, the shape of the bubbles is regular. It is clear that the majority of the bubbles were spherical owing to the surface tension. To understand the effect of different test times on the number of bubbles, we studied the bubbles captured in each set of 1600 images. Figure 4 shows a large difference in the density of bubbles in every experiment. Comparing the average density of bubbles calculated for each group of 10 experiments, the maximum difference in the number density of captured bubbles is about 150,000/cm3, indicating that the manual reciprocating motions greatly impact the number of bubbles produced.
Figure 5 displays the statistical histograms of the BSD in two example operations, showing that the bubble size distribution is very close to the log-normal distribution, which is a feasible model used to describe the microbubble size distribution in the experiment. The expression for log-normal distribution is shown as follows (24) :