A multiscale mass transfer model for gas–solid riser flows: Part 1 — Sub-grid model and simple tests

A review of multiscale CFD for gas–solid CFB modeling

“…One reason is the expectation that the heat/mass transfer rate is high in a CFB and therefore of minor effects to the overall reaction rate. For example, the reaction coefficient k r of ozone decomposition over FCC particles was reported of the order of magnitude of 10 s À1 , while that of the overall mass transfer coefficient k p a p was 10 5 s À1 (Ouyang et al, 1995;Dong et al, 2008a). That means, the overall performance is controlled by reaction rate and the mass transfer is negligible (Damköhler number Da ¼ k r =k p a p ( 1) in the case that the flow is regarded homogeneous.…”

“…The other branch is termed the ''variational", it correlates movements between the fine-and coarse-grids (or scales) by invoking a variational stability condition, which is exemplified by the energy minimization multiscale (EMMS) model (Li and Kwauk, 1994) and its extensions, e.g. EMMS/matrix for flow modeling and EMMS/ mass for reaction modeling (Dong et al, 2008a).…”

“…(3)-(5) were simplified in that all terms related with @=@t; @=@r except @=@z were ignored (Dong et al, 2008a). With the structure parameters from EMMS, the solution of Eqs.…”

Experimental and theoretical investigation of mass transfer in a circulating fluidized bed

“…Recent years have seen more reports on the deterioration of mass and heat transfer efficiency between gas and solid in CFBs due to clusters; see for example Hou et al, 2010aHou et al, , 2010bChalermsinsuwan et al, 2009aChalermsinsuwan et al, , 2009bDong et al, 2008aDong et al, , 2008b. However, these have been based on theoretical analyses and little experimental evidence is available to validate the models.…”

Approaching virtual process engineering with exploring mesoscience

“…The EMMS drag model has now been applied widely because of its effectiveness at upgrading CFD. Extensive studies has been carried out at our institute by validating the model via simulations of the various aspects of the hydrodynamics of lab and pilot scale CFB units [38,39,[41][42][43][44][45][46][47][48][49][50][51][52][53][54][55], studying its relationship with classical continuum models and therefore formulating structure-dependent continuum models [56][57][58][59][60], doing various industrial projects [61][62][63][64][65][66][67][68] and extending the model to (i) consider the effect of heat and mass transfer as well as chemical reaction [69][70][71][72][73], (ii) consider the effect of particle size distribution [74,75], (iii) simulate the hydrodynamics of bubbling and turbulent fluidization [76][77][78][79] and (iv) the gas-liquid and gas-liquid-solid systems [40,[80][81]…”