Nina Shapley
Department of Chemical Engineering, Columbia University.
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Flows of emulsions in which the volume fraction of droplets is high (>30%) are found in many applications in the food, pharmaceutical and oil industries. In most studies of emulsion rheology and processing, the emulsion is assumed to be homogeneous and the flow well-characterized, often without experimental verification in highly concentrated systems, which are opaque. We use nuclear magnetic resonance imaging (NMRI) to investigate concentration and velocity profiles noninvasively and in situ within flowing, concentrated, oil-in-water emulsions. The emulsions undergo shear flow generated in a horizontal, wide-gap, concentric-cylinder geometry. We observe partially counter-rotating flows in homogeneous, concentrated emulsions when the velocity of the outer cylinder is sufficiently low. Theoretical analysis suggests that this complex flow phenomenon is driven by buoyancy effects. Also, we show that the kinetics of mixing and mixing patterns in an inhomogeneous, concentrated emulsion are quite different from those observed in bulk liquids. Complex flows and unusual mixing patterns in emulsions have not been reported previously. Results such as these are relevant to many processing flows of dispersions. |
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