Numerical study of thermocapillary driven flow of a microbubble on locally heated wall

Two-dimensional numerical simulations of underwater vapor bubble on a hot spot have been performed to investigate the thermocapillary-driven flow generated at the bubble interface and the accompanying flow near the contact line. With fixing the bubble diameter of 10 µm, several contact angle and hot-spot temperatures have been considered to discuss the flow characteristics relevant to a mechanism of the particle accumulation in the bubble underneath, which was demonstrated experimentally in literature. In this study, the volume-of-fluid method was employed to capture the vapor-water interface, in the framework of OpenFOAM, an open-source CFD toolbox. We found that a bilayer structure is formed near the contact line, and the lower layer forms a flow approaching the contact line along the wall surface. In addition, a region where the wall shear rate decreases locally occurs slightly outside of the contact line. These two features are especially pronounced in the condition with contact angle of 30^◦ and with a high temperature of the hot spot. The thickness of this lower layer depends on the hot-spot temperature, and is estimated approximately at 200 nm in a present condition.