The fluidisation phenomena of Geldart A, compared to the other three types (Geldart C, B and D), is featured with a homogeneous bed expansion between minimum fluidisation and bubbling velocities. The characteristics of Geldart A particles in fluidisation have been extensively studied in the past, but mainly at a macroscopic scale. Recently, a combined approach of discrete element method (DEM) and computational fluid dynamics (CFD) has been applied to further the understanding at a microscopic, particle scale, but mainly under two-dimensional DEM conditions. In this work, three-dimensional DEM coupled with two-dimensional CFD is used to investigate the fluidisation behavior of Geldart A particles. The different behaviours such as fixed bed, bed expansion and bubbling bed are identified, which is in good agreement with the experimental observation. Bed expansion is then analyzed in detail in terms of particle-fluid and particle-particle interaction forces in relation to the flow structure. The results are shown to be qualitatively consistent with the previous two-dimensional CFD-DEM findings but quantitatively more reliable. The structural and force analysis is useful for a better understanding of the behavior.

Keywords: fluidisation, fine particles, bed expansion, discrete element method, computational fluid dynamics