Velocity measurement of thermocapilary flows around a single vapor bubble of FC-72

Abstract

The importance of studying thermal phenomena that occurred near the vapor bubbles during boiling is crucial, like for instance in the field of Aerospatiale. Under specific conditions, convective motions, known as the Marangoni convection, can be observed at the liquid vapor interface. In order to study this convective effect, while avoiding effects due to bubbles coalescence, we focused on the case of a single vapor bubble growing underneath a heating element in a non-degassed subcooled liquid (FC-72). Experiments were carried out under normal conditions of gravity and pressure, and for various levels of liquid subcooling and wall heat flux. To characterize the Marangoni convection around a single vapor bubble in the presence of a temperature gradient, we used two optical metrology methods: Shadowgraphy and Particle Tracking Velocimetry (PTV). Threshold from stationary to oscillatory mode was investigated and found to be influenced by both wall heat flux and level of subcooling. Velocity vector fields in the vertical axis of the bubble were obtained for various thermal parameters, and maximum velocities in the convective rolls determined.