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Cluster-induced deagglomeration in dilute gas-solid flows of cohesive particles

Banff International Research Station for Mathematical Innovation and Discovery

We study dilute gas-solid flows of cohesive grains in unbounded fluidization via CFD-DEM simulations, focusing on two types of heterogeneities: particle clusters of hydrodynamic origin and agglomerates of cohesive origin. Clusters refer to the regions of higher solid concentrations than surroundings, while agglomerates are particles held together by cohesive forces. Both heterogeneities have significant impacts on reaction rates, heat and mass transfer in multiphase flows. By tracking enduring contacts, we isolate agglomerates from the overall system heterogeneities quantified by local particle number density fluctuations. We found that with increasing system volume, the degree of clustering increases, while agglomeration decreases, contrary to the behavior of granular (no fluid) systems, where clustering enhances agglomeration due to the reduced relative velocities of particles in clusters. Based on statistical and theoretical analyses of particle velocities, higher levels of clustering in larger systems are shown to result in increased relative velocities between the gas and solid phases. This increased relative velocity between the phases serves as an added source of granular temperature, thereby enhancing deagglomeration. We coin this newly-identified mechanism as â cluster-induced deagglomerationâ and demonstrate its robustness in systems with increasing cohesion, where saturating agglomeration level with increasing cohesion is observed, as opposed to the monotonic behavior in granular systems.

Mathematics; Fluid mechanics; Scientific computing

video/mp4

Author affiliation: University of Colorado

2019-03-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/69124

Unreviewed

http://creativecommons.org/licenses/by-nc-nd/4.0/