Fine-grid two-fluid modeling of fluidization of Geldart A particles

•The fidelity of fine-grid TFM declines with the increase of gas velocity.•Meso-scale modeling is necessary for simulation of circulating fluidized bed.•Solids flux is critical to evaluate simulation of circulating fluidized bed.

A series of fine-grid simulation with two-fluid model (TFM) is performed for bubbling, turbulent and circulating fluidized beds (CFB) with Geldart A particles. The results show that the fine-grid TFM with homogeneous drag seems feasible for simulation of low-velocity, bubbling fluidized beds. However, the fidelity of fine-grid TFM declines with the increase of gas velocity. In particular, the solids flux predicted deviates much from the experimental data of CFB though the clustering phenomenon can be captured with refinement of grid. In contrast, the structure-dependent approach as exemplified by the energy-minimization multi-scale (EMMS)-based multi-fluid model gives better agreement with experimental data. This discrepancy raises the question of the applicability of the local equilibrium assumption underlying the TFM. It also sheds light to the necessity of meso-scale modeling and the critical role of solids flux to evaluate the simulation of CFB.

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