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Experiments were conducted of the low-Reynolds number breakup and separation of oil–particle clusters characterized by a high volume fraction of relatively large solid particles, under simple shear in an aqueous solution. The breakup of such oil–particle clusters, and the separation of particles from the clusters, are evaluated as a function of viscosity ratio of the oil phase to the aqueous solution, interfacial tension, and shearing time. When the viscosity ratio is high, clusters are more difficult to breakup, a longer shear time is needed, and few particles detach. At low viscosity ratios, clusters are easily deformed and break up into smaller clusters, and more clean particles detach. Lowering the interfacial tension also facilitates the liberation of oil droplets from particles. The results show that the breakup of oil–particle clusters with a high volume fraction of large particles can be characterized as simple droplet breakup, meaning that the viscosity of the oil governs the dynamics of the cluster, rather than an effective viscosity that is a function of the solid volume fraction. The degree of cluster breakup and the separation of particles from the primary cluster is related to a cluster-based capillary number and the viscosity ratio. There is a critical capillary number required to obtain clean particles. |
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