Observations of flow patterns in a spray dryer

Experiments have been performed on a pilot scale, cylinder-on-cone spray dryer fitted with a vaned-wheel atomiser to observe air flow patterns, with and without water spray. A combination of tufts, smoke streams and a laser light sheet, was used to provide information about regions of recirculation, flow stability, spray trajectories and wall deposition. While atomiser-induced swirl dominated the flow patterns under typical operating conditions, some instability was observed, although different in type, for situations with and without atomiser rotation. Clockwise eddies were observed to form and collapse between the wall and the strongly anti-clockwise swirling core created by anti-clockwise atomiser rotation. Without swirl, large portions of the recirculation zones at the walls were observed to have a weak tendency to change randomly between clockwise, anti-clockwise and chaotic behaviour.