Review of experimental study on drop breakup time and breakup rate

In this study, we mainly focus on the breakup time and breakup rate generated upon drop breakup. Corresponding researches in the literature were reviewed in this section.
The drop breakup time is an important parameter to understand the mechanism of drop breakup. At present, the parameter was obtained mainly by single drop experiments. Heskech et al.42 measured a limited number of drop breakup events and obtained the breakup time of silicone oil in a horizontal pipeline. The results showed that the breakup time was 19-59 ms for the mother drop with size 3.40-4.55 mm. Eastwood et al.16 found that the elongated drop can break up owing to capillary effects. Meanwhile, they pointed out that the viscosity of the dispersed phase is an important parameter affecting the breakup time. Andersson and Andersson43 carried out single drop breakup experiments in turbulent flows. They compared the breakup time of drops with the turbulent time scales and pointed out that only large turbulent eddies are effective in drop breakup43. Maaß and Kraume30investigated the drop breakup time in a rectangular channel where a single blade was fixed internally. Their statistical criterion of breakup time is the duration of the whole process from the drop entering the flow field to the final breakup. It should be noted that this time often includes circulation time, where the drop may remain subspherical. On the premise above, they found that the breakup time is not a const but approximately obey a β -distribution for the drop of a certain size. Furthermore, they discussed the breakup time based on the peak values of the β -distribution. Experimental data showed that the breakup time monotonically increases with increasing of the drop diameter and decreases with increasing of the energy dissipation rate. Solsvik and Jakobsen34 measured the breakup time by single drop breakup experiments in a stirred tank. They scaled the breakup time as the duration taken from the initial deformation of a spherical mother drop to the terminus where the fragments were totally generated. They further defined the breakup process as the breakup cascade37. According to their study, the breakup time holds a significant dependence on the drop diameter and increases monotonously with the increase of drop size. Ashar et al.36 measured the time for droplet deformation in a rotor-stator mixer. They found out that the breakup time is positively scaled with the weber number. Meanwhile, they point out that turbulent eddies with the size close to the target drop control the breakup process.
Despite researchers provided important experimental data of drop breakup time through single drop experiments, the quantitative laws of how physical properties and operating parameters influence the breakup time are still limited. Moreover, the sufficiently predictable model for drop breakup time is also in lack.
Recently, experiments have been carried out by Li’s group to measure the breakup rate directly in a pulsed disc and doughnut column38–40,44 and in a pump-mixer41,45. In the above study, the multiple breakup process is treated mathematically as a sequence of the binary breakup. In this study, experimental data of the breakup rate are also provided. Moreover, we make a systematic analysis of the process of multiple breakage and probe into the influence rules of different factors on multiple breakup.