Particle distribution in unbaffled stirred vessels

Abstract

The present work is devoted to providing an insight into the solid-particle distribution within top-covered unbaffled stirred tanks via purposely collected local experimental data. Experiments were carried out on a labscale unbaffled stirred tank by making use of a recently introduced technique named Laser Sheet Image Analysis (LSIA). In its original formulation, the technique includes an image post-processing procedure to delete reflection effects on results. In the framework of the present work, a method combining the use of purposely produced fluorescent particles and a suitable camera high pass filter was devised and presented. Results collected with (new method) and without (old fashion) fluorescent particles were compared for comparison purposes and a satisfactory agreement was found, thus validating both the procedures devised to delete reflections. LSIA technique in the novel version was used to investigate the distribution of solid particles at different agitation speeds in an unbaffled tank stirred by either a marine propeller or by a Rushton turbine. On overall, collected results show that the propeller configuration provides somewhat better particle distribution throughout the tank as compared with Rushton turbine operated at the same agitation speed. The two stable toroidal attractors for solid particles there observed are recognizable also here, though with a configuration significantly different due to the diverse flow fields.