Effect of cold wall temperature on onset of oscillatory thermocapillary flow

Abstract

Oscillatory thermocapillary flow is investigated experimentally in liquid bridges of high Prandtl number fluids. The effect of heat loss from the liquid free surface on the onset of oscillations is investigated. The heat loss is mainly due to the natural convection of air around the liquid bridge. The airflow is varied by varying the temperatures of the cold wall and the ambient air. It is found that when the free surface is nearly flat, the critical Marangoni number (Macr) decreases substantially with increasing heat loss, but when the surface is concave, Macr is not affected by the heat loss. The airflow around the liquid bridge is analyzed numerically, which shows a relatively weak airflow caused by the heating and cooling done in the experiment. It is shown that the computed Biot number correlates the Macr data well.