A study of the effect of drag-reducing surfactants on flow patterns in stirred vessels

The analysis of velocity data in a stirred vessel, obtained experimentally in this work by laser Doppler velocimetry, as well as from the literature, shows that the dissolution of a surfactant with a long alkyl chain - in this work, hexadecyl trimethyl ammonium bromide - and a counter ion with an aromatic group - in this work, sodium salicylate - can modify the mean and r.m.s. velocities of the liquid, a phenomenon similar to the drag reduction observed in tubular flows. The magnitude and importance of this effect depend on the concentration of the surfactant-counterion mixture and on the localization of the element of fluid in the vessel, i.e., in a zone close to the impeller or farther away from it, but not in a monotonic fashion.