Influence of geometrical aspect ratio on the oscillatory Marangoni convection in liquid bridges

Oscillatory Marangoni convection in silicone oil liquid bridges is investigated by three-dimensional, time-dependent numerical solutions of the model equations and by micro-scale experimentation. The field equations are numerically solved with three-dimensional control volume methods in a staggered cylindrical non-uniform grid. Two experimental configurations are utilized: 1) the two disks sustaining the bridges are made of copper, their temperatures are controlled with Peltier elements, the flow field in a vertical section is visualized by tracers illuminated by a laser light cut in the meridian plane and four fine temperature sensors are inserted axially from the hot disk into the liquid bridge; 2) the lower disk is made of copper and the upper one is made of transparent glass, heated by an electrical resistance, for visual measurements in a cross section orthogonal to the liquid bridge axis. The surface temperature distribution is measured by an infrared thermocamera. It is shown that the flow field organization, depending on the critical wave number, is related to the geometrical aspect ratio of the liquid bridge and that smaller is the aspect ratio, larger is the critical wave number and more complex the flow-field structure. For each aspect ratio considered, the flow field exhibits a first transition from the axy-symmetric steady to a standing wave instability model and then a second transition from the standing wave to the travelling wave regime. The influence of buoyancy effects on the oscillatory Marangoni flow organization is investigated by heating the liquid bridges either from above or from below.