EFFECTS OF SURFACE-ACTIVE MATERIALS ON THE HYDRODYNAMIC DEVELOPMENT IN A LIQUID JET

The oscillating jet method is interesting for the study of the evolution of the dynamical surface tension as a function of the age of the surface in the range of the 0.5-90 msec. The experimental results obtained by this method, using the Bohr equation, depend on the dimensions and the shape of the nozzle as well as on the flow rate. More or less reasonable correction factors have been introduced to take into account the hydrodynamic development in the jet. In order to understand the phenomena which limit the use of the Bohr equation, particularly in the vicinity of the nozzle, we have studied the velocity profiles in a cylindrical jet by Laser Doppler Anemometry (LDA). We have studied the hydrodynamic relaxation in the jet, and we show the importance of the surface rheologic effects induced by the surfactants at high concentration. Hence the LDA applied to the jet surface velocity measurements allows us to know the age evolution along the jet surface and can be used to refine the oscillating jet method, provided of course that the fluid is transparent. © 1979.