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Granular Flow: Coal Hoppers and Pebble Bed Reactors

Granular materials, common in everyday experience, are critical in many industrial processes, and exhibit complex mixed liquid-like/solid-like behavior and microscale stress inhomogeneities. Together with Sandia National Lab, we have built large-scale simulations of an experimental pebblebed nuclear reactor design, featuring 440,000 6 cm spherical particles that are slowly cycled through a cylindrical container, to analyze particle mixing between fuel and moderator. Our 3D homogenized multi-scale method breaks flow into correlated motions of small groups of particles (3-5), and accurately reproduces discrete element simulations of granular hopper drainage two orders of magnitude faster. It can continuously preserve particle packing constraints during the duration of the flow and accurately track both the radial distribution function and bond angle distribution function. The algorithm and resulting software are now used in coal power plants to do real-time control of delivery of different qualities of coal: as an example, an Ohio plant uses RFID tags to calibrate initial free parameters. (On right, screenshot of spot model software developed to control fuel mixing in a coal-fired power plant, with different colors corresponding to different coal qualities.)