(43e) Computational Fluid Dynamics Simulation of Compressible Non-Newtonian Biomass in a Compression-Screw Feeder
In this work a customized constitutive model was implemented in the open-source CFD package OpenFOAM  in order to simulate concentrated biomass as a highly viscous non-Newtonian fluid in the screw feeder. The biomass is modeled as a single-phase compressible Bingham fluid with a plastic viscosity as well as a density-dependent yield stress. The compressibility formulation (pressure-dependent density) and the density-dependent yield stress formulation in the governing equations follow from a recent study by Duncan et al. .
A pilot-scale hopper/screw feeding system at NREL  was 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 from 10 to 60 rpm in a conical throat that contains anti-rotational grooves. The predicted torque and pressure increase at the exit agree with experimental data for biomass feedstocks with varying rheological properties and auger rotating speeds. The analysis of the stress forces helped to identify the critical conditions were excessive wear, jamming, and blowback could occur.
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