Simulation of the effects of inlet swirl on gas flow patterns in a pilot-scale spray dryer

Simulations of the transient flow behaviour in a pilot scale spray dryer are presented in order to investigate the effect of the inlet swirl on the flow stability within the dryer. The simulations use the transient Reynolds-averaged Navier-Stokes equations, closed via the shear stress transport (SST) turbulence model, solved using the CFX5 commercial CFD code. The results are shown to be in good agreement with the experimental data and further highlight the importance of transient phenomena in short form spray dryers. The modelling shows significant differences between the no swirl case, where a central air jet is seen to wobble with large-scale eddying motion outside the dryer axis, through strong precession of the central air jet at moderate swirl to vortex breakdown with reverse flow occurring on the axis of the dryer at high swirl.