A comparison of models for the evaporation of the Lennard-Jones fluid

The evaporation of a thin liquid film is studied by a diffuse interface model whose thermodynamic and transport properties are consistent with those of the Lennard-Jones fluid. Solutions are obtained for various liquid film temperatures and downstream vapor flow velocities. The results are compared with reference molecular dynamics simulations of a system of atoms interacting by the 6-12 Lenard-Jones potential. It is shown that the diffuse interface model underestimates the temperature drop across the non-equilibrium vapor region next to the liquid-vapor interface but overestimates the density drop, thus predicting smaller evaporation rates. Results indicates that the discrepancies between molecular dynamics and diffuse interface model predictions become smaller when the liquid film temperature approaches the critical temperature and the vapor becomes a dense, non-ideal gas. Further successful comparisons of molecular dynamics results with the predictions of a hybrid model, combining the continuum description of the liquid with the kinetic description of the vapor, suggest that the observed discrepancies can be attributed to poor description of the Knudsen layer provided by the diffuse interface model when the vapor phase is dilute.