Numerical study of oil-water emulsion formation in stirred vessels: effect of impeller speed
Abstract
The mixing of immiscible oil and water by a pitched blade turbine in a cylindrical vessel is studied numerically.
Three-dimensional simulations combined with a hybrid front-tracking/level-set method are employed to capture
the complex flow and interfacial dynamics. A large eddy simulation approach, with a Lilly-Smagorinsky model, is
employed to simulate the turbulent two-phase dynamics at large Re = 5663 - 56632. The numerical predictions
are validated against previous experimental work involving single-drop breakup in a stirred vessel. For small Re,
the interface is deformed but does not reach the impeller hub, assuming instead the shape of a Newton’s Bucket.
As the rotating speed increases, the deforming interface attaches to the impeller hub which leads to the formation
of long ligaments that subsequently break up into small droplets. For the largest Re studied, the system dynamics
becomes extremely complex wherein the creation of ligaments, their breakup, and the coalescence of drops occur
simultaneously. The simulation outcomes are presented in terms of spatio-temporal evolution of the interface shape
and vortical structures. The results of a drop size analysis in terms of the evolution of the number of drops, and
their size distribution, is also presented as a parametric function of Re.
Origin : Publisher files allowed on an open archive