Structure-dependent multi-fluid model for mass transfer and reactions in gas-solid fluidized beds

A fluidized bed reactor embraces complex coupling among flow, heat/mass transfer and reaction kinetics over a wide range of spatial-temporal scales, on which the meso-scale structure in forms of bubble or cluster plays the critical role. The traditional two-fluid model (TFM) is based on local equilibrium assumption and neglects the effects of sub-grid meso-scale structures, thus, it is not suitable for simulating dense, heterogeneous gas-solid riser flow. To be consistent with the meso-scale characteristics, we proposed a structure-dependent multi-fluid model (SFM), It reduces to the conventional two-fluid model (TFM) if local equilibrium or homogeneity is assumed within each grid, and reverts to the energy-minimization multi-scale (EMMS) model if it is used to describe global behavior of a fluidized bed. The multiscale CFD based on SFM and EMMS drag has been successfully applied in simulating gas-solid fluidized bed flows in recent years. In this work, we will extend such approach to the realm of reactive flows with mass transfer and reactions. The heterogeneity indexes for reaction and mass transfer are thereby defined, which may facilitate TFM-based reactive simulations with structure-dependent corrections. Two experiments of ozone decomposition in circulating fluidized beds are simulated to validate this approach with comparison to data. (C) 2014 Elsevier Ltd. All rights reserved