The effect of swirl on flow stability in spray dryers

The effect of varying the amount of inlet air swirl on the stability of the flow patterns in a small-scale, co-current spray dryer has been investigat ed. The objective of this work was better understanding of the effect of th e vane angle on the flow patterns and to determine whether a particular van e angle provided superior performance. The dryer studied was a cylinder on cone unit, with a drying chamber 0.8 m in diameter and 1.61 m tall, and fit ted with adjustable swirl vanes tightly surrounding a Delavan GA1 two-fluid atomiser. Swirl vane angles between 0 degrees and 45 degrees, in 5 degrees increments, were investigated using a complementary combination of how vis ualisation and laser Doppler velocimetry (LDV) techniques. No single swirl vane angle resulted in behaviour that was clearly steady throughout the dry er, but a swirl vane angle of about 25 degrees was considered to be an appr opriate selection. This vane angle, corresponding to a Swirl number of appr oximately 0.45, gave an observable degree of stability in much of the flow domain and good air-spray mixing without excessive spreading of the spray c loud and wall deposition. The introduction of spray had a significant effec t on the flow behaviour, so that air-only studies did not adequately repres ent the flow conditions with spray.