Experimental measurement and numerical simulation of the effect of swirl on flow stability in spray dryers

A 0.29 m, 0.5 m tall, hydraulic model of an industrial spray dryer, constru cted from perspex, has been used to study the precession of the central jet of air inside this equipment, where this central jet may be connected to t he occurrence of wall deposits inside this equipment,. Experiments showed t hat the Row was strongly time-dependent, with two characteristic frequencie s that depended on the angle of the inlet swirl vanes over a range of angle s from 0 degrees to 40 degrees. The main frequency of precession of the cen tral jet occurred over a time scale of a few seconds, and image analysis al lowed the characteristic frequencies of the precession to be quantitatively assessed. Numerical simulations of the flow, conducted with CFX5, a CFD pa ckage, predicted Strouhal numbers for the jet precession that were within e xperimental errors of those observed for no swirl and 40 degrees swirl, and only slightly outside the error bounds for 25 degrees swirl. This agreemen t suggests that the k - epsilon turbulence model is suitable for estimating the frequencies of precession in spray dryers. This is of industrial signi ficance, since the precession may be linked to the occurrence of wall depos its.