Experiments and Simulations of Gas-Solid Flow Dynamics with a Moving Porous Media Model

Continuous spatial particle atomic-layer deposition (ALD) reactors contain billions of fine and ultrafine particles under typical operating conditions. Simulating micron and submicron powders in a reactor with gas dosing zones on the order of centimeters presents a significant modeling challenge. However, experiments and CFD-DEM simulations in MFIX have revealed that the powder bed moves as a solid plug under typical vibratory convection conditions, so we decided to take advantage of the low relative motion between particles by approximating the powder bed as a porous media. A moving porous media model, which utilizes the sliding and layering dynamic mesh capabilities in ANSYS Fluent, was developed to enable efficient simulations of reactor-scale multiphase flow in the continuous vibrating beds used for particle ALD. Treating the packed powder bed as a solid skeleton with an infiltrating gas phase circumvents the computational expense associated with resolving particle-particle collisions. Simulations revealed the effects of packed bed and porous baseplate permeability, vibration intensity, and precursor/purge gas velocity ratios on the flow behavior inside continuous spatial particle ALD reactors. Understanding and predicting the reactor-scale behavior enables process optimization under different reactor conditions.