Figure Captions
FIGURE 1 Schematic of the experimental apparatus.
FIGURE 2 Bubble growth, departure and coalescence from a downward-pointing nozzle captured under illumination by a mental-halide light.
FIGURE 3 (a) Close-up of bubble coalescence recorded by a LED light (R 0=0.085 mm, Q =1299 ml/min), (b) Detailed process of surface-wave travel and pinch-off recorded in a mental-halide light (R 0=0.085 mm, Q =1400 ml/min), (c) Another side-view of pinch-off and liquid jet recorded in a LED light (R 0=0.085 mm, Q =1191 ml/min).
FIGURE 4 Superimposed profiles spanning the travel of capillary waves and pinch-off shown in Figure 3(b).
FIGURE 5 Typical bubble behaviors from an upward-pointing nozzle recorded under illumination by a LED light (R 0=0.085 mm, Q =54.4 ml/h).
FIGURE 6 . An illustration of the formation process of microbubbles.
FIGURE 7 Normalized pinch-off time by the capillary time versus Ohnesorge number of mother bubble.
FIGURE 8 Phase diagram for partial coalescence depending on Ohnesorge number of mother bubble and relative size of parent bubbles.
FIGURE 9 Phase diagram for no bubble coalescence (I), coalescence without pinch-off (II), coalescence with generation of microbubbles (III), and irregular coalescence (IV) depending on Weber and Bond numbers.
FIGURE 10 Variation in microbubble size for different values of Weber and Bond numbers.
FIGURE 11 Distribution of normalized microbubble diameter by its average value.
FIGURE 12 (a) Comparison of Eq. (10) with experimental data. The solid line fits the experimental data following the trend (Ds /Lb )/Bo9/20∝We1/4. The error bar on the exponent is 3/40 and two bounds are plotted with dotted lines, (b) Ratio of satellite surface energy to the kinetic energy of the gas flow. The solid line fits the experimental data following the trendEs /Ek ∝We-5/3.