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Slow granular flows play an important role in industries ranging from food to
pharmaceuticals to ceramics, and this subject has received much recent
attention in the literature. In contrast, heat transfer in even the simplest
particle flows is poorly understood. While it is clear that the conductivity
depends strongly on the microstructure of the bulk material, in granular flows,
the microstructure changes with time and the role of particle
mixing/segregation (i.e., "convective" heat transfer) quickly comes to the
fore. We have developed a multi-scale,multi-physics modeling technique --
Thermal Particle Dynamics (TPD) -- that can be used to examine transient heat
transfer in granular materials. Here, we focus on the role of stress chains,
particle convection, and interstitial fluids. Our results may be of interest to
those working on drying kilns, solid phase reactors, and some porous materials.
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- Thermal maps of a two-dimensional particle bed. The temperature front in a transiently heated granular bed does not propagate uniformly, as may be expected
using an effective medium approximation. Instead, the front oscillates as stress chains converge and diverge along the bed height. This figure shows snapshots
of a TPD simulation, an experiment, and a one-dimensional EMA simulation of a heated particle bed at three different times.
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- Quantitative comparison of TPD and experiment. Shown is the width-averaged temperature of the particle bed from above for both the TPD simulation (lines)
and the experiment (symbols). Note that the agreement is quite good without requiring any adjustable parameters. However, a consistent under-estimation is
observed which may be due to the small by finite conductivity of the gas still present during the experiments (this is captured by incorporating gas-solid
transport into the model).
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