Homogeneous and Nonhomogeneous Flow of the Particle Phase
Gas–particle flows are inherently oscillatory, and they manifest in nonhomogeneous structures. Thus, if one sets out to solve the microscopic two-fluid model equations for gas-particle flows, grid sizes of less than 10-particle diameter become essential. For most devices of practical (commercial) interest, such fine spatial grids and small time steps require significant computational time. Thus, the effect of the large-scale structures using coarse grids must be accounted for through appropriate modifications of the closures (i.e., drag model). Qualitatively, this is equivalent to an effectively larger apparent size for the particles.
In this chapter, two approaches are discussed that have gained significant attention in the literature: filtering (subgrid) and energy minimization multi-scale (EMMS).
KeywordsDrag Force Particle Volume Fraction Solid Volume Fraction Fluid Catalytic Crack Solid Flow
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