Thermocapillary Energy Transportation at Evaporating Liquid Surface*

A thermocapillary flow can be driven by interfacial temperature difference. However, the mechanism of thermocapillary energy transfer at the interface is still not fully understood, and the interfacial flow and its associated thermal distribution have not been well characterized. We have designed the experiments to generate the thermocapillary flow by arranging a thin line heater at the evaporating liquid surface, and we have observed the thermal patterns at the interface under the steady state evaporation conditions. A variety of thermal patterns under the infrared camera are characterized with the remarkable transition from the transporting latticed cells, then the unidirectional travelling fingers, to the counteractive travelling fingers. Before the occurrence of boiling near the thin heating line, the thermal pattern varies with the tangential heat flux at interface, the energy transferred by the thermocapillary flow is found to be proportional to the Marangoni velocity. The further relation is discussed.