I am trying to model evaporation of a droplet on a substrate in Comsol. I've managed to reproduce the methodology of the tutorial model "Droplet Evaporation on Solid Substrate" and it works fine. But in that model the contact angle is pi/2 and the contact line is free to move along the substrate so that the velocity of the droplet surface near the substrate (due to the shrinking of the evaporating droplet) is perfectly well defined by the evaporative mass flux through the droplet surface. This makes it possible to implement the droplet surface in the model as a fluid-fluid interface with a prescribed mass flux (calculated from the vapor concentration gradient just outside the droplet).
The problem is to include the pinning of the contact line so that the droplet evaporates with fixed contact area but diminishing contact angle. In this case the surface of the droplet is pinned at the contact line (or contact point in 2D) and is not therefore quite free to move - at the edge of the droplet - just where the evaporative mass flux is largest. The question is: can I still use the "fluid-fluid interface" / "free surface" boundary condition (with prescribed evaporative mass flux) for the droplet surface? Or do I have to implement the mesh deformation only manually by calculating the changing shape of the droplet from the integral of the evaporative mass flux over its entire surface?
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