Thermocapillary flow near a hemispherical bubble on a heated wall

Abstract

The flow driven by variations in surface tension round a hemispherical gas or vapour bubble on a heated wall has been investigated numerically for steady-state conditions over a wide range of values of dimensionless parameters, and experimentally for one set of conditions. Although six parameters are needed to specify the flow conditions, the magnitude of the liquid flow normal to the heated wall is determined primarily by tihe Marangoni number, Prandtl number and the Biot number based on the effective heat-transfer coefficient at the liquid-gas interface. The interior temperature of the bubble depends in addition on the thermal conductivity ratio of the liquid and the wall material. The flow is very sensitive t o the presence of surface-active contaminants. For water, calculations and experimental observations both indicate that contamination which lowers the static surface tension by only 0.1% may suppress the thermocapillary motion.