Highly swirling transient flows in spray dryers and consequent effect on modeling of particle deposition

Abstract

Cotton turf and hotwire measurements were used to experimentally assess the highly swirling flow characteristics in a spray dryer fitted with a rotary disc atomizer. The numerical simulation captured key features of the flow field. Analysis revealed that rapid rotation of an atomizing disc tends to centrifugally split the central inlet jet. The flow field exhibited significant long time-scale transient behaviour. However, this centrifugally split jet resulted in a balanced upward recirculation region in the chamber as expected by the jet-feedback mechanism. Detailed analysis using a 'transient air-steady particle' approach revealed that this approach is applicable for such highly swirling transient flows as well. However, caution should be exercised when interpreting the deposition results, particularly in regions of low particle velocities. This is anticipated be an important consideration in future attempts to simulate the predominantly transient flows in spray dryers. © 2011 The Institution of Chemical Engineers.