An experimental study of the effects of surfactant on a falling liquid film

Addition of surface active agents to a falling liquid film changes the fluid mechanical behavior of the film. In this study we describe, both by observations and by calculations, what happens with the wave pattern after an addition of surfactant. The experiments were carried out in a 6-m high falling film column with a mixture of water and glycerol. The changes in wave pattern were detected by a video camera. Addition of surfactant will influence the film differently for different surfactant concentrations. Surfactant concentrations under the saturation limit destabilize the film and concentrations over the limit stabilize the film. The surface excess concentration, the concentration of surfactant in the surface per square meter, plays a key role in the influence of surfactant on the behavior of falling liquid films.