Multi-scale CFD modeling of gas-solid bubbling fluidization accounting for sub-grid information

An improved bubble-based heterogeneous drag model was formulated in which the original bubble-based EMMS drag model at macroscale bed level was extended to microscale sub-grid level for accurate coarse-grid two-fluid modeling (TFM) of Geldart A powder bubbling fluidization. At both the macroscale and microscale levels, the physically heterogeneous structures were modeled by three pseudo phases, i.e., bubble phase, emulsion phase, and inter-phase, where conservation equations and a stability condition were applied at multi-scales present in a bubbling fluidized bed. This new improved bubble-based drag model utilizes a two-step macro-to-micro scheme, where the multi-scale drag coefficient is related to phase volume fractions, velocities, and accelerations within each coarse grid. 2D and 3D modeling results show that TFM combined with the improved drag model can accurately reproduce the heterogeneous structures in a laboratory-scale Geldart A powder bubbling fluidized bed. At relatively coarse grid, the predicted axial and radial distributions of solid concentration are in very good agreement with experimental measurements. This shows that our proposed new bubble-based drag model for TFM simulations is promising for simulation of large-scale Geldart A powder bubbling fluidization. (C) 2018 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.