Modelling of gas-solid-liquid flow and particle mixing in a rotary drum

Solid-liquid rotary drums have been widely practised in various industries, while the complex multiphase hydrodynamics hinders the understanding and optimisation of these apparatuses. In this work, the computational fluid dynamics-discrete element methoddata (CFD-DEM) coupled with volume of fluid (VOF) is developed to describe the gas-solid-liquid flow and mixing behaviours in a rotary drum considering inter-particle collisions, inter-phase interactions, and interface morphology. A smoothing method is used to link the quantities between the particle and computational grids, allowing the fine grids to resolve flow details such as the gas-liquid interface position and curvature. After model validations, the typical mixing behaviours of gas-solid-liquid flow in a rotary drum are studied. The effects of liquid presence and rotating speed on particle-scale behaviours (e.g., repose angle, active-passive zone depth, solid residence time and contact force chain) and the time evolved mixing performance (e.g., mixing index and dispersion) are studied. The results show a positive correlation of the active depth, mixing degree, and particle dispersion with the rotating speed. The liquid presence leads to a deeper active depth, prolonged solid residence time in the active zone, and lower contact force. The work sheds light on the design and process optimization of rotary drums.