HYDRODYNAMIC MODELING OF DROPLET COALESCENCE AT LIQUID LIQUID INTERFACES

Liquid-liquid dispersions consisting of a dispersed and a continuous liquid which are mutually unsoluble or at least almost unsoluble occur in many separation processes. On the one hand they are intentionally produced to achieve a high surface area per unit volume for heat and/or mass transfer, e.g., in the case of the solvent extraction. On the other hand such dispersions sometimes occur unintentionally, for instance. during the condensation of a heteroaceotropic mixture or in the frame of wastewater treatment, e.g., after oil accidents. Under almost all circumstances, the dispersions have to be separated into their clear homophases. Simple gravity settlers without any coalescing aids are applied in most cases for this purpose. Within such apparati the drops flow together ("coalesce") and form a coherent phase. This review discusses the physical models of gravity settlers. Calculation methods for the coalescence of single droplets and for the coalescence of droplet swarms in dense dispersions are reviewed. Finally, possibilities and limitations of hydrodynamic settler modeling are pointed out.