Experiments on the transition from the steady to the oscillatory Marangoni-convection of a floating zone under reduced gravity effect

The transition from the steady to the oscillatory Marangoni convection in a floating zone under reduced influence of the gravity is visualized by means of the already proved method of “light-cut-technique”. The Marangoni convection is caused by a negative temperature gradient from the upper to the lower copper plug, whose diameter is kept to a small magnitude of 3 mm Φ to obtain a small Bond's number. By this way the micro-gravity effect in respect to the Marangoni convection can be simulated. From the visualization and the simultaneous measurements of the local temperature the range of the Marangoni number for the transition is determined. A strong correlation exists between the observed period of the oscillation of the branching streamline between the two vortices on the plane with the axis of the floating zone on one hand and the period of the temperature oscillation on the other hand. A model conception for the physical mechanism is introduced to understand this oscillatory instability.