Jetting behavior as a bubble bursts in free space

The phenomenon of bubble bursting is very common in nature and is of prime importance in various technologies and industrial processes. Similar to interfacial bubbles, the process of a bubble bursting in free space, that is, the rupture of bubbles surrounded by air, often results in jet flows. However, the location and mechanism of the jet flows are different from those produced by interfacial bubbles. This paper describes the results of several experiments conducted to investigate the behavior of a bubble bursting in free space, especially the jet flows that occur at the end of the process. The results show that viscosity has a strong inhibitory effect on both the droplets (film drops and jet drops) and the jet resulting from bubble bursting. Based on experimental results, we establish a phase diagram for the jetting behavior in terms of the Reynolds number (Re) and the Ohnesorge number (Oh) and discover the existence of threshold conditions. Jetting occurs in the zone where Oh is less than some threshold value Oh(c) and Re is greater than some threshold value Re-c, whereas a liquid clump appears in the zone where Oh > Oh(c) and Re < Re-c. For 0.002 < Oh < 0.272 and 65 < Re < 52633, we find that Re-c = 503 +/- 136 and Oh(c) = 0.079 +/- 0.001. A schematic of the events that occur during bubble bursting depicting the forces at play is subsequently analyzed, and the role of viscosity at the moment of jetting is highlighted. The results of this study can be used to inhibit or increase the formation of droplets in numerous applications.