Thumbnail Image

Diffusion limited evaporation of a binary liquid film

Chatwell, René Spencer; Heinen, Matthias; Vrabec, Jadran

FG Thermodynamik und Thermische Verfahrenstechnik

An analytical solution of a model fluid’s time behavior, known as the Stefan problem, is presented. A scenario is investigated in which a planar two-component liquid film is continuously evaporating into a thermodynamically non-ideal vapor phase. Evaporation is initiated and maintained by a spatial chemical potential gradient, while its rate is limited by the components’ diffusion fluxes across the vapor-liquid interface. Local thermodynamic equilibrium is found to be present throughout the process. In contrast to the classical approach relying on equations of state, all required non-idealities are formulated in relation to the Gibbs energy and are determined by molecular simulations. Initially, the liquid is an equimolar mixture of two components of different volatility, whereas the adjacent vapor phase is dominated by a dense inert gas. To validate the analytical model and verify all exploited assumptions, the results are contrasted to large scale molecular dynamics simulations.