Numerical probing of a low velocity concurrent pilot scale spray drying tower for mono-disperse particle production – Unusual characteristics and possible improvements

A pilot scale micro-fluidic-spray-dryer (MFJSD-II) utilizing a single-stream atomization to produce mono-disperse particles has been developed at Monash University. A unique feature of this unit is the use of relatively low air velocities in the range of 10−1–10−2 m s−1, which increases the residence time of the particles during the drying process, in comparison with conventional spray dryers. In this study, Computational Fluid Dynamics (CFD) simulation revealed that the effects of natural convection, caused by heat loss from the wall, were significant in deflecting the flows of air from the central jet-side recirculation pattern, causing them to spread towards the wall. The flow patterns formed a layer of relatively high velocity region adjacent to the wall. The understanding of these flow patterns would be crucial for future designs of low-velocity spray dryers. The spreading of the central jet towards the wall also created recirculation regions in the center of the tower, thus affecting the residence times particularly for smaller particles. More numerical simulations are required to optimize the design of the bottom bustle to be effectively used as a particle-separator.