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

TL;DR

This paper investigates the dynamics of the triple contact line on a non-isothermal heater during partial wetting, revealing the effects of superheating, evaporation, and the limitations of classical slip conditions, with new modeling approaches proposed.

Contribution

It introduces a non-stationary contact line model considering evaporation and condensation, and proposes an augmented slip condition to address hydrodynamic singularities.

Findings

Small superheating causes evaporation of the adsorption film.

Classical Navier slip condition cannot relax the contact line singularity.

The proposed second derivative slip condition improves modeling accuracy.

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.