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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.

in Wiley InterScience (www.interscience.wiley.com).While an understanding of the dynamics of segregation has begun to emerge, controlling segregation continues to be a complicated problem. The use of time-modulation-via selective baffle placement-in order to suppress segregation in rotating tumblers is explored. Bidisperse (size or density), cohesionless granular materials in quasi-two-dimensional (2-D) rotating containers are studied by means of simulations and experiments. Results are presented in two main configurations for the placement of the baffles, (1) axial placement, and (2) attached to the periphery of the tumbler. Both experiments and simulations indicate that baffles attached at the periphery are ineffective in reducing segregation, while baffles axially located in the tumbler generate periodic flow inversions and dramatically reduce both density and size segregation. Qualitative and quantitative evidence is presented, in terms of the intensity of segregation. Theoretical and scale-up arguments are provided for the practical implementation of this approach.

Periodic flow inversions have been shown as an effective means to eliminate both density (D system) and size (S system) segregation. The frequency of these inversions, however, is the key to applying this technique and is directly related to the inverse of the characteristic time of segregation. In this work, we study size segregation (S system) and adapt a size segregation model to compliment existing work on density segregation, and ultimately aid in determining the critical forcing frequency for S systems. We determine the impact on mixing/segregation of both the binary size ratio and the length of each leg of a "zig-zag chute". Mixing is observed when L <Ū tS, where L,Ū , and tS denote the length of each leg of the zig-zag chute, the average streamwise flow velocity of the particle, and the characteristic time of segregation, respectively.