Vortex behaviour of an unbaffled surface aerator

Agitating liquids in an unbaffled surface aeration tank leads to the formation of a vortex in the region of the impeller shaft. The types and characteristics of the vortex govern the process phenomena of a surface aeration tank. In the present work, experimental results and empirical correlations have been obtained to relate the vortex depth to a number of physical factors. Experiments have been carried out on geometrically similar surface aeration systems, so that the present results can be simulated in the field conditions. The critical speed at which the vortex reaches the impeller has been estimated. It is found that around critical speed, there is an observable change in mass transfer characteristics, power used for mixing, and radius of the forced vortex zone. Equations for predicting vortex depth in geometrically similar surface aeration tanks have also been developed.