Experimental Measurement and Numerical Simulation of the Effect of Swirl on Flow Stability in Spray Dryers

Abstract

A 0.29 m, 0.5 m tall, hydraulic model of an industrial spray dryer, constructed 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 the occurrence of wall deposits inside this equipment,. Experiments showed that the flow was strongly time-dependent, with two characteristic frequencies that depended on the angle of the inlet swirl vanes over a range of angles from 0° to 40°. The main frequency of precession of the central jet occurred over a time scale of a few seconds, and image analysis allowed the characteristic frequencies of the precession to be quantitatively assessed. Numerical simulations of the flow, conducted with CFX5, a CFD package, predicted Strouhal numbers for the jet precession that were within experimental errors of those observed for no swirl and 40° swirl, and only slightly outside the error bounds for 25° swirl. This agreement suggests that the k – ɛ turbulence model is suitable for estimating the frequencies of precession in spray dryers. This is of industrial significance, since the precession may be linked to the occurrence of wall deposits.