Local evaporation flux affected by thermocapillary convection transition at an evaporating droplet

Steady-state water evaporation experiments on a stainless steel funnel demonstrate that the local evaporation fluxes are uniform before the thermocapillary convection transition at an evaporation droplet. If a thermocapillary flow is present, the local evaporation fluxes become nonuniform along the interface as a result of effects of thermal conduction from both liquid and vapour phases and thermocapillary convection at the interface. The global evaporation rate was found to be relative to the local evaporation rate influenced by the thermocapillary flow at the interface. Statistical rate theory was applied to predict the saturation pressure locally at the measured positions. It was found that the vapour-phase pressures along the interface are parabolic once thermocapillary convection exists. But the mean of local vapour-phase pressures is consistent with the global vapour-phase pressure measured above the interface.