(237k) Computational Fluid Dynamics Simulation of Lignocellulosic Biomass Transport in a Compression-Screw Feeder
Continuum simulations of the rotating screw feeders present a unique challenge regarding the resolution of rotating interfaces along with baffle like features on the stator surface. We utilize the dynamic-mesh capabilities in the open-source CFD toolbox, OpenFOAM, where the screw is embedded in a cylindrical mesh that slides with respect to a stationary background grid for the stator surfaces. The biomass feedstock is modeled as a compressible Bingham fluid . The non-Newtonian transport model includes a plastic viscosity as well as a density dependent yield stress component. We also modify the low Mach solvers in OpenFOAM to incorporate an equation of state compatible with pressure-density variations for different biomass feedstocks. A pilot-scale hopper/screw feeding system at NREL  is used to compare the experimental observations with our simulation results. The auger is 280 mm long and tapered with outer diameter changing from 80 mm to 35 mm. The auger rotates at 2-10 rad/s in a conical throat which contains anti-rotational bars. The simulations will be used to determine important operational parameters such as the dependence of torque with respect to varying solids fractions and different biomass feedstocks.
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