A New Method to Investigate the Suspension of Solid Particles in Rectangular Tanks Agitated by a Source-Line Bubble Plumes

Abstract

It is well known that when mechanically agitated vessels are used, the forces applied by the agitator moving in the fluid contained in the vessel maintain flow patterns in the fluid. In the tanks under study, the flow patterns are maintained by an air curtain rising within the vessel. The movement produced by this air curtain interchanges fluid between different parts of the vessel, maintains particle suspension and promotes gentle mixing that has applications in the field of biotechnology. The experimental work carried out in this article is focused on the study of mixing and the behavior of solid particles, using an air curtain as the means of mixing. The research included the fluid motion visualized by white polystyrene beads, video recording and a new method to investigate the suspension of solid particles. The new method introduced an index of deviation from acceptable suspension and was used as a tool to select the best design of tank-aerator combination suitable for suspension. Experimentally, the suspension was found to be a function of air flow rate and the type of aerator used. Two distinct factors were identified, namely, the aerator location and the shape of the aerated tank. It was confirmed that the best location was in the middle of the tank, and the minimum air flow rate to keep all the particles in suspension was reached when the aerated surface was a rectangular surface in which the length is twice the width. In addition, a relationship between fluid velocity, air flow rate, flow patterns and baffles disposition are discussed. Finally, a correlation for the velocity in the liquid was developed and found to be adequate in the scale-up of aerated tanks agitated by an air curtain.