Particle-scale modelling of gas-solid flow in fluidisation

Various approaches have been proposed to model the gas-solid two-phase flow at different time and length scales, including the so-called two-fluid model (TFM), direct numerical simulation (DNS) and combined continuum and discrete model (CCDM). This paper briefly discusses the key features of these models and their relative merit with special reference to modelling gas fluidisation. Focus is then given to CCDM in which the motion of individual particles is obtained by solving Newton's second law of motion and fluid flow by the Navier-Stokes equation based on the concept of local average. The applicability of CCDM is highlighted by its successful simulation of complicated phenomena associated with the transition between fluid-like and solid-like behaviour in raceway formation and bed expansion. At the same time, the usefulness of the resulting particle-scale information is demonstrated in elucidating the fundamentals governing the gas-solid flow. Finally, areas for future development are discussed.