Visualization of free surface phenomena using photochromic dye

Surface tension variation along a gas-liquid interface has a considerable effect on flow near the interface. In order to clarify this, the so-called Marangoni effect, we observed the prevention of natural convection by the surface tension change due to a contaminant in a cavity. The velocity profiles near the interface were measured by the photochromic dye activation method, and the surface tension gradient and the contaminant concentration distribution along the interface were determined. Development of a stagnant surface region induced by contaminant accumulation was theoretically investigated. The theory agreed well with the experimental results. A surface spreading motion due to the Marangoni effect was also investigated using an ultraviolet laser beam, and all the experimental results were correlated with dimensional analysis considering the surface tension variation due to the ionization.