Modeling Axial Mixing of Fuel Particles in the Dense Region of a Fluidized Bed

A semiempirical model for the axial mixing of fuel particles in the dense region of a fluidized bed is presented and validated against experimental magnetic particle tracking in a fluid-dynamically downscaled fluidized bed (Kohleret al. Powder Technol., 2017, 316, 492-499) that resembles hot, large-scale conditions. The model divides the bottom region into three mixing zones: a rising bubble wake solid zone, a zone with sinking emulsion solids, and the splash zone above the dense bed. In the emulsion zone, which is crucial for the mixing, the axial motion of the fuel particle is shown to be satisfactorily described by a force balance that applies experimental values from the literature and an apparent emulsion viscosity of Newtonian character. In contrast, the values derived from the literature for key model parameters related to the bubble wake zone (such as the upward velocity of the tracer), which are derived from measurements carried out under cold laboratory-scale conditions, are known to underestimate systematically the measurements relevant to hot large-scale conditions. When applying values measured in a fluid-dynamically downscaled fluidized bed (Kohler et al. Powder Technol., 2017, 316, 492-499), the modeled axial mixing of fuel tracers shows good agreement with the experimental data.