Abstract Summary (Max 250 words)
When contacting two immiscible liquids in stirred vessels, there exists a minimum impeller speed, NJD, to completely incorporate the dispersed phase. We develop a model based on the energy or force balance approach developed for solid-liquid mixing studies (Baldi et al., 1978; Davies, 1986; Grenville et al., 2015). Similar to solid liquid, the model strikes a balance between the disruptive forces of the turbulent eddies and the dispersed phase buoyancy, however, unlike with solids, the liquid pool breaks up into smaller and small droplets until a balance is struck and so interfacial forces and viscous forces are also considered. To test this model appropriately, the continuous and dispersed phase physical properties (interfacial tension, viscosity, density) are varied using several model fluids and additives. The study is conducted primarily in 305mm diameter vessels with select experiments conducted in 450 and 610mm diameter vessels to evaluate scale-up. The majority of impeller configurations investigated consisted of dual wide blade hydrofoils (MHS), triple counterflow impellers, and dual paddles (SLS). NJD was determined visually in triplicate by incrementally increasing the impeller speed until no remaining floating undispersed organic remained. Impeller reaction torque was measured using an air bearing. The initial model is found to fit the experimental data better when a model is used to estimate a mixture or emulsion viscosity opposed to using the continuous phase. Furthermore, the experiments suggest that the 305mm diameter vessel behaves differently than the larger scale vessels.
