QUANTIFICATION OF THE PERFORMANCE OF AGITATORS IN STIRRED VESSELS - DEFINITION AND USE OF AN AGITATION INDEX

An agitation index, based on velocity measurements obtained from laser Doppler velocimetry or other similar techniques, is proposed as an ob jective measure of the effectiveness of a particular agitator in induc ing flow in a stirred vessel. This index is calculated by first genera ting a cell structure based on the measurement grid, and then assignin g each velocity to the entire corresponding cell; the volume-weighted sum of velocities yields then the agitation index, which represents th e volume-average velocity as a percentage of the impeller tip velocity . The usefulness of this objective measure of the quality of agitation in a stirred vessel is illustrated by applying it first to the case w here three different agitators have to be graded in terms of effective ness in inducing flow, and then to the case of determining the clearan ce of two agitators located on the same shaft corresponding to the opt imum liquid circulation.