By introducing periodic flow inversions, we show both experimentally and computationally that forcing with a value above a critical frequency can effectively eliminate both density and size segregation. The critical frequency is related to the inverse of the characteristic time of segregation and is shown to scale with the shear rate of the particle flow. This observation could lead to new designs for a vast array of particle processing applications and suggests a new way for researchers to think about segregation problems.
We experimentally examine a dilute suspension of non-neutrally buoyant spherical particles migrating in a simple mixing tank at small but finite Reynolds numbers. We observe that the particles spontaneously migrate to repeatable non-trivial asymptotic locations within toroidal structures, located above and below at-disk impellers. The asymptotic migration positions include both the exact center of the torus and intermediate higher-order cluster locations within the flow whose stability is dependent on flow andparticle conditions. Furthermore, we note that the particle clusters seem to coincide with the location of unmixed islands within the underlying fluid flow. We also observe a migratory competition when multiple particles are introduced into the flow.
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