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 objective measure of the effectiveness of a particular agitator in inducing flow in a stirred vessel. This index is calculated by first generating a cell structure based on the measurement grid, and then assigning each velocity to the entire corresponding cell; the volume-weighted sum of velocities yields then the agitation index, which represents the 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 where three different agitators have to be graded in terms of effectiveness in inducing flow, and then to the case of determining the clearance of two agitators located on the same shaft corresponding to the optimum liquid circulation.