Heat and mass transfer across the vapor-liquid interface: A comparison of molecular dynamics and the Enskog-Vlasov kinetic model

Due to the intricacies of the interface between vapor and liquid, evaporation and condensation processes are not fully understood. The small spatial extent of the interface renders experimental studies on this subject challenging so that computational investigations are indispensable. For two heat and mass transfer scenarios across a vapor-liquid interface, molecular dynamics simulation is compared with the direct simulation Monte Carlo solution of the Enskog-Vlasov kinetic equation. A heat flux from the vapor to the liquid in a closed system as well as classical evaporation into an open half-space are considered. In both scenarios, temperature and one-dimensional driving gradients are widely varied, sampling systems containing 5 & sdot; 105 molecules. Since the two simulation methods rest on different potential models for the molecular interactions, a meaningful transformation between the truncated and shifted Lennard-Jones fluid and the Sutherland fluid is proposed. Spatially resolved density, temperature and velocity profiles from these simulation methods are consistent, except for the interface width. Consequently, particle flux and downstream pressure match as well. The good agreement between the results reinforces the validity of these approaches. The study is accompanied by successful comparisons of these simulations to kinetic gas theory with respect to macroscopic property variations at the interface.