Apr 2023
Fluidized bed reactor is a multiphase flow, dissipative system, featuring meso-scale, heterogeneous flow structures with bimodal distributions of parameters. To grasp this characteristic, recent years have witnessed a blossom of the meso-scale modeling in multiphase flows. In particular, by integrating bimodal distributions into the structure-dependent conservation laws of the mass, momentum and energy, we can unify the hydrodynamic equations of the two-fluid model (TFM) and those of the energy minimization multi-scale (EMMS) model. Further, by extending this structure-dependent analysis to the extremum tendency of the energy dissipation or entropy production, we find that the principle of minimum energy dissipation rate applies only to the uniform flow in gas-dominated, pneumatic transport flow regime, but fails in dense fluidization regimes. In contrast, the EMMS-based stability condition enables a good prediction of heterogeneous flow structures in fluidization, and thereby the choking transition in circulating fluidized beds. By integrating the EMMS-based drag, mass and heat transfer models into the structure-dependent multi-fluid model (SFM), we have developed the multi-scale computational fluid dynamics approach, and successfully applied it in simulations of various fluidized bed reactors, including e.g., fluid catalytic cracking (FCC) risers, fluidized bed combustors, gasifiers, and methanol to olefins (MTO) reactors.