Abstract
Many industrially relevant emulsification devices are of the high-energy type, where drop deformation and subsequent breakup, take place due to intense turbulent fluid–drop interactions. This includes high-pressure homogenizers as well as rotor-stator mixers (also known as high-shear mixers) of various designs. The stress acting on a drop in a turbulent flow field varies over time, occasionally reaching values far exceeding its time-averaged value, but only during limited stretches of time, after which it decreases down to low values again. This it is one factor separating turbulent from laminar emulsification. This contribution reviews attempts to take this intermittently time-varying stress into account in models predicting the characteristic drop diameter resulting from emulsification experiments, focusing on industrially applicable emulsification devices. Two main frameworks are discussed: the Kolmogorov–Hinze framework and the oscillatory resonance framework. Modelling suggestions are critically discussed and compared, with the intention to answer how critical it is to correctly capture this time-varying stress in emulsification modelling. The review is concluded by a list of suggestions for future investigations.
Highlights
Emulsion formation under turbulent flow conditions has a large industrial relevance, with applications ranging from food, pharmaceutical and petrochemical to general chemical processing
Much of the turbulent drop breakup literature has been developed as extensions and Much of theofturbulent breakup literature been developed as extensions and re‐evaluations laminar drop breakup theory
The same stress balance reasoning can be used to describe the dynamic response in terms of how the shape of the drop evolves with time when passing through the laminar flow in the four-roller mill (i.e., predicting L(t) and B(t))
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. That this stochastic time-varying behavior of turbulent stresses plays a role in turbulent drop breakup was realized already by Kolmogorov [7] in his seminal paper from 1949. The intention with this contribution is to critically review the different attempts to include stochastic time-variations in modelling turbulent breakup, focusing on the two modelling frameworks intended to predict the largest drop size surviving a turbulent device, e.g., the Kolmogorov–Hinze framework and the oscillatory resonance framework.
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