  Motivated by the evaporation of soap films, which has a significant effect on
their lifetime, we performed an experimental study on the evaporation of
vertical surfaces with model systems based on hydrogels. From the analogy
between heat and mass transfer, we adopt a model describing the natural
convection in the gas phase due to a density contrast between dry and saturated
air. Our measurements show a good agreement with this model, both in terms of
scaling law with the Grashof number and in terms of order of magnitude. We
discuss the corrections to take into account, notably the contribution of edge
effects, which have a small but visible contribution when lateral and bottom
surface areas are not negligible compared to the main evaporating surface area.
