Effects of free surface heat transfer and shape on thermocapillary flow of high Prandtl number fluids

The main objective of the present work is to study the effect of free surface heat transfer on the thermocapillary flow of high Prandtl number fluids. The effect of free surface heat transfer is investigated experimentally and numerically in the liquid bridge configuration. A numerical code basing on the finite volume method is used to simulate the steady liquid flow and airflow. The air motion is simulated in order to compute the free surface heat transfer rates for given experimental conditions. The numerical analysis in liquid bridges shows different flow structures between heat gain and loss cases. The relationships between the onset of oscillatory thermocapillary flows and free surface heat transfer in the bridge geometry are identified.; The free surface heat transfer has a significant effect on the onset of oscillatory flow in liquid bridges with a nearly cylindrical surface. The critical temperature difference, or the critical Marangoni number, is very sensitive to the heat loss from the free surface. The dynamic free surface deformation in the hot corner is very important and responsible for the observed heat loss effect. Namely the S-parameter correlates with the critical conditions well under the heat loss conditions.; The heat transfer from the free surface has no effect on liquid bridges with a highly concave free surface. The critical Marangoni number remains constant and also predicts the onset of oscillations well for liquid bridges with a nearly cylindrical free surface under net heat gain conditions and liquid bridges with a highly concave free surface under heat gain/loss conditions.; Two different physical mechanisms of transition from steady thermocapillary flow to oscillatory thermocapillary flow in liquid bridges of high Prandtl number fluids are responsible for the observed oscillation phenomena. One is the interaction between the surface heat loss and dynamic free surface deformation in the hot corner for liquid bridges with a nearly cylindrical free surface. The other is the azimuthal propagation of hydrothermal waves without surface deformation for liquid bridges with a nearly cylindrical free surface under heat gain conditions and liquid bridges with a highly concave free surface.