Design and operation of unbaffled vessels agitated with an unsteadily forward–reverse rotating impeller handling solid–liquid dispersions

Abstract

ABSTRACTAn unbaffled vessel, which is an enhanced form of solid‐liquid apparatus, has been constructed; when fitted with an agitator using an impeller it rotates unsteadily in the alternate direction, i.e. a forward–reverse rotating impeller. For this type of solid–liquid agitation vessel, a disk turbine impeller with six flat blades was used; suspension of solid particles in liquid was studied on different apparatus scales. Empirical relations to predict the minimum impeller rotation rate for complete solid suspension were presented with variations in the solid–liquid conditions and apparatus geometrical conditions, including the scale effect. The agitation requirements for complete solid suspension were related to the liquid flow along the bottom of the vessel which is assumed to enhance off‐bottom suspension of solid particles. For off‐bottom suspension of solid particles, an effective flow characteristic produced by the forward–reverse rotating impeller set at a lower height was recognized from the viewpoint of the intensity of turbulence in the liquid flow. Copyright © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.