Effective rates of coalescence in oil–water dispersions under constant shear

Abstract

We report destabilization of highly stable oil–water emulsion under shear. Prior studies on shear induced coalescence are restricted to lower volume fraction (up to 20%) of dispersed phase. In this contribution, the effect of shear induced coalescence in a larger range of volume fractions of dispersed phase, and shear rates, is presented. The experimental ranges have practical relevance in the context of industrial coalescers which exploit low shear to coalesce oil–water emulsions. For our work, a synthetic emulsion mimicking the properties of medium-heavy crude is subjected to simple shear. In summary, the studies reveal the effect of shear rate, volume fraction of dispersed phase and viscosity ratio on the evolving drop size distributions of oil phase. For low shear rates and volume fractions, the evolving drop size distributions show a bimodal distribution, while a multimodal nature of drop size population was observed for higher dispersed phase volume fraction (40%), something which has never been reported thus far. Finally, a population balance model employing diameter based coalescence kernel is used to rationalize the time evolution of droplet size distributions.