Multicomponent Droplet Evaporation in a Geometric Volume-of-fluid Framework

This work proposes an innovative model for multicomponent phase change in interface-resolved simulations. The two-phase system is described by a geometric Volume-Of-Fluid (VOF) approach, and considers multiple components in non-isothermal environments, relaxing the hypothesis of pure liquid droplets usually studied in the literature. The model includes the Stefan flow and implements the following solutions for the complications that arise when studying liquid mixtures: i) a coupled approach for solving the interface jump conditions; ii) a proper strategy to obtain a liquid velocity for the advection of the volume fraction field, also applicable to static droplets with strong density ratio; iii) and a geometric approach to discretize the scalar fields transport equations. This model was implemented in the open-source code Basilisk, and it was tested on a number of benchmark phase change problems, such as the fixed flux evaporation, the Stefan problem, Epstein Plesset, and the Scriven problem. These test cases demonstrate the convergence of the numerical methods to the analytical solutions. More complex configurations, such as multicomponent isothermal and non-isothermal droplets are compared using numerical benchmark solutions obtained assuming spherical symmetry. The code, as well as the simulation setups, are released on the Basilisk website, making it the first model and open-source implementation of multicomponent phase change in a VOF framework.