Contacting of process gases and small solid particles in circulating fluidized beds finds widespread application in the petroleum, chemical and power generation industries. The interpenetrating-continua (or two-fluid) modeling approach seems very promising for realistic modeling of the detailed hydrodynamics of gas-solids flows. Its application could greatly benefit commercial process design, scale-up and optimization. Despite the proliferation of models and software, however, very little guidance is available in the literature for the confident formulation and interpretation of model predictions. A factor that contributes to such skepticism is the lack of a clear understanding of the fundamental underlying mechanisms which generate the predicted flow behavior. This contribution attempts to elucidate the effect of different model terms for the idealized case of fully-develooped riser flow. Two one-dimensional and two two-dimensional models based on Fluent 4.3 (commercial CFD software from Fluent, Inc.) were applied to a relatively dense suspension flow. Markedly different hydrodynamics were predicted from the different models which is indicative of the pitfalls that await the casual modeler.
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