(679j) Tip Streaming: A Possible Mechanism for the Formation of Extremely Fine Droplets in Aqueous-Bitumen Mixtures

Processes such as centrifugation and inclined settling are currently used to achieve the separation of water and solids from bitumen froth in the oil-sands industry.  They are, however, ineffective in removing water droplets that are about or less than a micron in size.  These droplets can form a significant fraction of the residual water content in diluted bitumen after separation.  The aim of this project is to understand the mechanisms of formation of these fine water droplets, and to suggest remedies to mitigate their production.  Our current focus is to assess if the combination of hydrodynamics and oil-water interfacial properties could be leading to the formation of small droplets.   Preliminary experiments were performed in a co-flowing device with a water-bitumen system.    Under certain conditions, we observed extremely fine threads of the core aqueous fluid (less than 1.5 microns in diameter, a limitation of our camera), produced by the extensional stresses imposed by the bitumen phase.  Notably, these micron and sub-micron sized threads produced by tip streaming occurred for capillary numbers that were below the capillary numbers for dripping.  This implies that there could be mixing conditions where drops could stretch and tip stream to produce fine droplets, but not break up.  We explore the effects of bitumen dilution, asphaltene concentration, naphthenate concentration, pH and solvent aromaticity on the tip-streaming phenomenon.