THE BEHAVIOR OF DRAG-REDUCING CATIONIC SURFACTANT SOLUTIONS

The behavior of two types of drag reducing surfactant solutions was studied in turbulent flows in pipes of different diameters. The investigated surfactant systems contained rod-like micelles; they consisted of equimolar mixtures of n-tetradecyltrimethylammonium bromide, n-hexadecyltrimethylammonium bromide, and sodium salicylate. The structure of the turbulence was studied using a laser-Doppler anemometer in a 50 mm pipe. In the turbulent flow regime both surfactant solutions exhibited characteristic flow regimes. These flow regimes can be influenced by changing the amount of excess salt, the surfactant concentration, or the temperature. The shape of the turbulent velocity profile depends on the flow regime. In the turbulent flow regime at low Reynolds numbers, velocity profiles similar to those observed for dilute polymer solutions are found, whereas at maximum drag reduction conditions more 'S-shaped' profiles that show deviations from a logarithmic profile occur. An attempt is made to explain the drag reduction by rod-like micelles by combining the results of the rheological and the turbulence structure measurements.