Characterization of Agitation Intensity in Flocculation Processes

Abstract

It is common practice in the design and evaluation of flocculation processes to use the velocity gradient determined from the mean power input (reported as G) as the principal indicator of agitation intensity. This practice is objectionable because agitated vessels are notoriously nonhomogeneous, floc breakup occurs primarily in the impeller stream, and interparticle contact and subsequently aggregation require relative particle velocity, which in turn is caused by eddies of a particular scale or wave number. Data are presented in this work that show that the dissipation rate per unit mass in the impeller stream can exceed the mean value by two orders of magnitude or more. It is important that modeling efforts take these factors into account.