Resistivities across the vapor–liquid interface of a simple fluid: An assessment of methods

Abstract

Heat and mass transfer across the interface between liquid and vapor is studied by means of molecular dynamics simulation. Two scenarios are considered to access the interface resistivities, specifying either the evaporation rate or the temperature gradient. Spatially resolved profiles of density, temperature, chemical potential, pressure tensor elements, and hydrodynamic velocity are sampled with large-scale molecular dynamics simulations to elucidate the structural and dynamic properties across the interface under non-equilibrium conditions. The employed interaction model is appropriate for simple fluids, like argon, while its thermodynamic properties in bulk phases are fully known. Most of the temperature range from the triple point to the critical point is investigated, varying the heat flux and the particle flux over one to two orders of magnitude. Different approaches are followed to determine the interface resistivities, and their results are compared to literature data and kinetic gas theory. It is found that the interface resistivities are a sole function of the interface temperature and are independent of the chemical potential gradient or the temperature gradient. This also holds for its thickness and surface tension up to the very large gradients that are typically imposed in molecular dynamics simulations. It stands to reason that this is also the case under the presence of gradients with a magnitude that is technically relevant and thus much smaller.