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.