  The evaporation of sessile droplets on a flat surface involves a complex
interplay between phase change, diffusion, advection and surface forces. In an
attempt to significantly reduce the complexity of the problem and to make it
manageable, we propose a simple model hinged on a surface free energy-based
relaxation dynamics of the droplet shape, a diffusive evaporation model and a
contact line pinning mechanism governed by a yield stress. Our model reproduces
the known dynamics of droplet shape relaxation and of droplet evaporation, both
in the absence and in the presence of contact line pinning. We show that shape
relaxation during evaporation significantly affects the lifetime of a drop. We
find that the dependence of the evaporation time on the initial contact angle
is a function of the competition between the shape relaxation and evaporation,
and is strongly affected by any contact line pinning.
