Dynamics of the triple contact line on a non-isothermal heater at partial wetting

Abstract

The dynamics of the triple gas-liquid-solid contact line is analysed for the case where the gas is the saturated vapour corresponding to the liquid, like in the vapour bubble in boiling. It is shown that even small superheating (with respect to the saturation temperature) causes evaporation of the adsorption liquid film and the true triple contact is established. It is shown that the hydrodynamic contact line singularity cannot be relaxed with the Navier slip condition under such circumstances. Augmented with the second derivative slip condition is proposed to be applied. For the partial wetting conditions, a non-stationary contact line problem where the contact line motion is caused by evaporation or condensation is treated in the lubrication approximation in the vicinity of the contact line. High heat fluxes in this region require the transient heat conduction inside the heater to be accounted for. Two 2D problems, those of drop retraction with no phase change and of drop evaporation are solved and analysed as illustrations of the proposed approach.