Experimental results on Marangoni flows at a gallium surface

Main objective of this experimental development was to provide a cavity filled with a free-surface liquid metal in order to perform model experiments with low Prandtl-number fluids. The main technical problem was to avoid or, at least, to control oxidation of the liquid metal surface. This was solved by a novel finite volume technique which will be described in the lecture. Liquid Gallium was chosen as model fluid. A controlled amount of oxides was used as tracer at the other-wise free Ga surface. The following phenomena were up to now studied with the help of this container:

• Marangoni flows and their instabilities due to an imposed thermal gradient
• thermoelectrically driven flows,
• oscillating melting and solidification fronts.

Most of the results will be presented in video form. Surprisingly, the Marangoni flow direction is for small temperature differences from hot to cold corresponding to a positive derivative and a maximum in the surface tension temperature dependence. Main conclusion is that this technique providing a controlled free liquid metal surface represents a novel experimental approach to study low Prandtl-number thermocapillary flows, solidification, instabilities or thermoelectricity on the level of model experiments.