Influence of co-axial airflow and volume ratio on thermo-capillary convection in half floating zones

Abstract

Present work is an extensive numerical investigation of interfacial flow in 5 cSt silicone oil that develops under the action of thermo-capillary force and interaction of this flow with the surrounding air motion using the commercial software ANSYS Fluent 17.2. The physical model is a half floating zone of high Prandtl number fluid (Pr = 56) co-axially surrounded by ambient air under microgravity conditions. The surface of a slender liquid bridge (VR = 0.9) is subjected to parallel air stream which is co-directed and counter-directed with the thermo-capillary flow along the interface. This forced air motion influences the basic flow in the system via shear stress and heat transfer at the interface. The effect of ambient air velocity and the volume ratio of the liquid bridge on the evolution of flow states is examined by performing axisymmetric computations in both liquid and air domains. The considered values of air velocity are comparable or larger than the Marangoni velocity to account for the shear action employed by the parallel airflow. The results show that the heat loss at the interface characterized in terms of local Biot number is significantly higher in case of counter-directed airflow as compared to that of co-directed airflow. By varying the volume ratio of the liquid bridge (0.90 < VR < 1.10), the resulting alteration in surface velocity and temperature of thermo-capillary flow is found to affect the flow dynamics of the system. Thermo-capillary convection inside slender liquid bridge results in more heated core liquid region as compared to that of fat liquid bridge affecting the heat transfer condition at the free surface. The authors report a significant influence of the flow and geometric parameters on the stationary flow solution.