CFD-DEM Investigation of Spout Stabilization by Large-Particle Addition.

Stable spouting of small particles is critical in fluidized-bed chemical vapor deposition (FB-CVD), but spout deflection, channeling, and irregular flow often occur. In this study, cold-model experiments and CFD-DEM simulations were combined to investigate the effects of particle diameter and density on spouting stability in a pseudotwo-dimensional (pseudo-2D) spouted bed. Particles of four materials were tested at different diameters: glass beads (2.6 g/cm3), ZrO2 (5.6 g/cm3), Fe (7.8 g/cm3), and UO2 (10.8 g/cm3). Unstable, transitional, and stable regimes were classified by power spectral density (PSD) analysis of pressure-drop fluctuations. Under the tested conditions, more stable spouting was obtained with larger or denser particles. In an unstable small-particle ZrO2 system, spout deflection was progressively suppressed by adding large particles. A PSD peak power-diameter ratio-density stability phase diagram was constructed for the tested conditions. Three coupled stabilization mechanisms were further identified by the CFD-DEM simulations. Momentum exchange and kinetic energy dissipation were increased through large-small collisions. Drag was distributed more uniformly in the spout. Local high-velocity channels and spout deflection were consequently suppressed, and centerline-symmetric particle circulation was established. These results provide laboratory-scale mechanistic evidence for stabilizing small, high-density particles under cold-model conditions. They also provide hydrodynamic insights relevant to nuclear fuel particle coating. Future studies will extend this investigation to fully three-dimensional, thermochemically representative systems and further evaluate its applicability to industrial FB-CVD reactors.