The influence of impeller type on mean drop size and drop size distribution in an agitated vessel

Abstract

In most work on agitated liquid–liquid dispersions, Rushton turbines have been used. Here, mean drop size and drop size distributions are reported for six different impellers covering 3 generic types over a range of mean specific energy dissipation rates. Both viscous and non-viscous dispersed phases have been used at concentrations by volume of 1 and 5%. It has been found that at the same mean specific energy dissipation rate, low power number impellers (whether of the so-called “ultra-high shear” or “high flow” type) all produced similar sized drops at equilibrium which were much smaller than those found with two “high shear”, high power number impellers, i.e., the standard Rushton turbine and another six-blade disc impeller. By considering the energy dissipation rate to be confined to the impeller swept volume, these equilibrium drop size could be approximately correlated. The low power number impellers also achieved that equilibrium more rapidly and the drop size distributions in the dispersions produced by them were narrower than those formed when agitated by the Rushton turbine and the other six-blade disc impeller. However, further analysis of the flow in the impeller region and the inclusion of advanced coalescence models would appear to be required in order to enhance the interpretation of these results.