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Flow Patterns in Sudden Expansions and Their Relevance to Understanding the Behaviour of Spray Dryers
Author(s) -
Guo B.,
Fletcher D.F.,
Langrish T.A.G.
Publication year - 2002
Publication title -
developments in chemical engineering and mineral processing
Language(s) - English
Resource type - Journals
eISSN - 1932-2143
pISSN - 0969-1855
DOI - 10.1002/apj.5500100406
Subject(s) - mechanics , precession , strouhal number , turbulence , vortex , computational fluid dynamics , jet (fluid) , flow (mathematics) , physics , rotational symmetry , fluid dynamics , classical mechanics , reynolds number , condensed matter physics
The relevance of understanding the fundamental fluid dynamics behaviour inside spray dryers is demonstrated in this work, with such understanding being particularly important in studying the flow stability and wall deposition behaviour. CFD (Computational Fluid Dynamics) simulations, with the standard k‐ε model for turbulence, can predict the regular oscillatory behaviour of the inlet air jets observed experimentally in two‐dimensional planar sudden expansions and three‐dimensional axisymmetric expansions. In addition, CFD can predict experimentally‐observed Strouhal numbers very closely (within 10%) for the precession of the central jet in sudden expansions with small expansion ratios of about two, over a range of swirl numbers from zero up to vortex breakdown. As the expansion ratio is increased, different modes are predicted as the swirl number is increased, in terms of the precession direction, spiral direction relative to the swirl direction, and presence of vortex breakdown. Finally, CFD simulations have been found to be applicable for predicting the precession frequencies of the central jet in real spray dryer geometries.