Multiple breakup refers to a sequence of events through which a single
droplet eventually produces multiple daughter droplets at a given flow
condition. It is a more common phenomenon than binary breakup assumed in
the existing breakage kernel models. Using phase-field lattice Boltzmann
method, this work investigates the effects of Reynolds number, capillary
number and soluble surfactant on multiple breakup in shear flow. We find
that the critical capillary number in multiple breakup decreases as
Reynolds number increases, and the regime map for a surfactant-free
system could be classified into the non-breakup, elementary breakup,
multiple breakup, filament and coalescence regimes. In the system of
surfactants, the multiple breakup regime widens and the coalescence
regime narrows. A correlation is then proposed to predict the number of
breakup events and daughter droplets at a confinement ratio of 0.5. This
may provide some clues on developing new breakage kernels in population
balance modeling.