Dynamics of evaporating drops. Part I: formulation and evaporation model

Modifications in the rate of evaporation of a drop due to its surface deformation are investigated using numerical simulations based on a Galerkin finite element method. It is first shown that, for a drop at its boiling temperature and surrounded by a gas at a uniform temperature (far from the drop surface), the liquid and the gas phases may be studied separately, provided a large density ratio. In this paper the results of the gas phase are presented. The surface of the drop is deformed using various spherical modes up to the eighth with amplitudes as large as 70% of the radius of the spherical drop. The mass transfer number is also varied from 0.1 to 2. The results show that the rate of evaporation increases with the increase of the amplitude of the surface deformation and varies significantly along the surface of the drop. A model has been extracted from the numerical results, which expresses the mass flux as a function of the surface curvature. The model is valid for surface amplitudes up to 10% of the drop radius.