A generalized drag Law for heterogeneous gas-solid flows in fluidized beds

•The local heterogeneity factor of a drag model, ψ, is presented.•The overall slip velocity represent the overall heterogeneity of a fluidized bed.•The local heterogeneity relates to the overall heterogeneity.•The QC-EMMS drag model is generalized in a wide range of conditions.•The generalization is verified at various cases with relative errors less than 10%.

An accurate drag model is key to simulating the fluidization process in circulating fluidized beds. Existing drag models only apply well to homogeneous gas solid flows or to some heterogeneous flows, but lack generalization. The present work generalizes the heterogeneous QC-EMMS drag model [12]. The particle heterogeneity was represented in the sub-model of the QC-EMMS model by introducing a local heterogeneity factor Ψ so that the meso-scale drag model varies with the operating conditions. The overall macroscopic heterogeneity is characterized by the Reynolds number (Re*) of the overall gas-solid slip velocity, which represents the fluidization state variations with the operating conditions. The relationship between the local heterogeneity, Ψ, and the overall heterogeneity, Re*, indirectly relates the local drag force to the operating conditions via the cluster sub-model to generalize the QC-EMMS model. The model is incorporated into the two-fluid method to simulate the gas-solid flow behavior in a riser, with the results for various working modes verifying the model accuracy with relative differences all less than 10%.

Graphical abstractFigure: Generalization process: relationship between the heterogeneity factor, ψ, and Re⁎Figure optionsDownload full-size imageDownload as PowerPoint slide