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The air flow patterns in an industrial milk powder spray dryer were investigated. Isothermal three-dimensional transient simulations were carried out using the commercial CFD code CFX10.0. The Shear Stress Transport (SST) turbulence model was implemented to model the effects of turbulence.These simulations differ from previously published studies of spray dryer air flows in that they include features found in industrial scale plant. First, they include a second inlet air stream through the internal fluid bed at the bottom of the drying chamber. Second, the two outlet ducts are located near the top rather than the bottom of the dryer, which has been the case in most previous studies.It was found that the main air jet oscillated and precessed about the central axis. In turn, the recirculation zones between the main jet and the chamber walls fluctuated in size relative to the movement of the jet.Validation was achieved by observing the oscillation of the main air jet of a large dryer visualised by tell-tail tufts attached to a central pole.

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