Boiling and evaporation model for liquid-gas flows: A sharp and conservative method based on the geometrical VOF approach

A novel phase change model is developed for the direct numerical simulations of the liquid-gas flows, devoting to the evaporation and boiling flows in the framework of the geometrical volume of fluid method. The main focus of the present work is to impose accurate jump conditions for heat and mass transfers across the interface, while the conservative properties of the governing equations are maintained. We tackle this problem by employing an embedded boundary method, which divides the computational domain into the liquid region and the gas region separately, besides, the application of the finite volume method enables us to conserve the energy and the mass precisely. Results are then presented for a series of benchmark problems, and the accuracy and the robustness of the numerical methods are validated. In particular, two very challenging numerical tests are simulated: a droplet levitating above a hot plate or a liquid pool whose temperature is much higher than the boiling temperature. This kind of problem, known as the Leidenfrost effect, is non-trivial in numerical simulations, because the boiling and the evaporation can occur simultaneously on different regions of the same liquid interface. In addition, very careful calculations are required in the thin film of saturated vapor which is entrapped between the bottom of the drop and the plate. We show that the newly implemented numerical methods can accurately reproduce experimental and theoretical results, serving as convincing evidence of the superiority of our method.