The application of coarse meshes enables the investigation of industrial scale reactors using kinetic theory based two-fluid models (TFM). Many sub-grid drag modifications have, therefore, been put forth by academic researchers to account for the effect of small unresolved scales on the resolved meso-scales in this case. However, all these models significantly differ in terms of their dependencies on the void fraction and on the particle slip velocity. We, therefore, thoroughly implemented the sub-grid drag models of (ⅰ) EMMS, (ⅱ) Kuipers, (ⅲ) Sundaresan and (ⅳ) Simonin and compared them to (ⅴ) our CD-Lab relation and to (ⅵ) the homogenous drag law of Wen and Yu in case of a three dimensional bubbling fluidized bed. The results are verified a fine grid reference simulation. It is shown that the latter is not able to determine the hydrodynamics of the bed properly. Even though the application of the different sub-gird drag models significantly impacts the flow of the solid, the superficial gas flow seems to be quite insensitive to the sub-grid drag model. In contrast, predictions of each drag modification of the bed expansion show fairly good agreement with the resolved results. However, it appears that the coarse grid simulations considerably overestimate the bubble rise velocity. Second, the CD-Lab modification is validated in case of a pseudo-2D bubbling fluidized bed. The numerical results obtained on a coarse gird demonstrate that the CD-Lab model reveals fairly good agreement with experimental data of bed expansion.
展开▼
