3. Hydrodynamics

A review of multiscale CFD for gas–solid CFB modeling

“…For example, tube diameter concerns whether the slugging can occur (Yang, 2004); a short riser may be affected significantly by the inlet/outlet effects, showing different profiles from those in a higher riser under the same operating conditions; different connections between the downcomer and the riser may cause different profiles of voidage (Li, 1994).…”

On the choice of mesoscale drag markers

“…Reflecting on the history of drag modeling, we find that the experimental approach 13,32,55 as discussed above was well developed before the numerical approach blossomed. In the numerical approach, the detailed flow field data can be directly used to determine the drag value, whereas such data are not available in the experimental and analytical approaches.…”

“…The formulation of the definitional relations of drag correction factors (Equations (), (), (A3), and (A4)) is inspired by the two‐step scheme for drag modeling, as practiced in the experimental approach 13,32 . In this approach, the measurement of the drag correction factor and the development of its constitutive relation are conducted in two steps separately.…”

“…In early experimental attempts, O'Brien and Syamlal 12 proposed their heterogeneous drag correlation from experiments of gas–solid circulating fluidized beds (CFBs) under two given solid fluxes. Li 13 proposed two drag correlations by fitting experimental data based on the steady‐state balance between the drag and gravity in the dense bottom and dilute top regions of a CFB riser. Application of these correlations is usually limited to specific operating conditions and material properties, which cannot, in principle, be extended to the other systems.…”

“…Coarse‐grid markers refer to the variables readily available on a computational grid of the TFM when correlating H d 11 . As an example, the experimentally obtained heterogeneous drag correlations 13 and some EMMS drag correlations 16,19–22 are usually expressed as a function of the mean voidage ( ε g ) for a specific set of the superficial gas velocity ( U g ) and/or solid flux ( G s ). Igci et al 10,28,34,35 modeled the heterogeneity index as a function of and filter size (Δ f ) using a numerical approach.…”