Introduction

Turbulent liquid-liquid dispersion is of critical important in areas of chemical engineering, such as solvent extraction1,2, chemical reaction3, and emulsion process4–6, etc. One of the key parameters in those systems is the dispersed phase size distribution, as it determines the contact area between two phases and thus controls the mass, momentum, and heat transfer rate. In the turbulent regime, the evolution of the drop size distribution (DSD) is caused by behaviors of drop breakage and coalescence.7–11 For the case where the volume fraction of the dispersed phased is very low, the influence of the drop coalescence on the DSD evolution can be omitted compared to the drop breakage. Thus, the time and space distribution of the particle size can be characterized by quantifying the drop breakup behavior. To achieve the goal above, it is necessary to carry out in-depth and detailed experimental and theoretical researches on the mechanism of the drop breakup.
In earlier experimental studies, the drop breakup data was usually reversely deduced from statistical analysis of the droplet size distribution.12–16 Correspondingly, researchers established various breakup models based on mathematical and mechanical analysis.17–23 This analytical method is still adopted by many researchers over the years. Conclusions based on this method might be well applied to specific devices and systems, but often have unverified extensibility and accuracy when applied to other application conditions. To understand dynamics of the drop breakup, the first job is to obtain the direct experimental data of drop breakup. Over the years, the development of high-speed camera technology has provided strong support for the observation of drop breakup behavior. Employing high-speed camera equipment, researchers carried out a series of experiments to explore the mechanism of drop breakup. Those works were performed with various systems, operating conditions, and different experimental facilities. The topic mainly focused on the following aspects: breakup possibility24–31, number of fragments24,25,28,32–37 and daughter drop size distribution24–26,28,29,33,35,38–41, etc. Despite much efforts that have been done to investigate the drop breakup, it is still a long way to adequately understand breakup phenomena due to the complexity of breakup dynamics in turbulent liquid-liquid dispersions. At present, the direct experimental study on drop breakup behavior, especially the study on breakup time and breakup rate which will be briefly reviewed in the next section, is still very limited.
Therefore, the drop breakup time and breakup rate were experimentally quantified in the present work. A series of experiments were designed to systematically investigate the influences of physical properties and operating conditions, and furtherly, corresponding mathematical models were built to predict the drop breakup time and breakup rate. The goal of this study is to obtain an in-depth understanding of drop breakup processes and to provide direct experimental data for the construction and verification of breakup models.
The study is organized as follows. In the next section, a brief review of the experimental investigation on drop breakup time and breakup rate is present. Whereafter, the experimental equipment and research methods adopted in this study are introduced in detail. External turbulence parameters affecting drop breakup are estimated. The experimental results for the breakup time, breakup rate and the problems of multiple fragmentations are discussed in the results and discussion section. Moreover, the modeling ideas of breakup time existing in the literature are summarized and analyzed in this section. Finally, the conclusion is present in the last section.