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.