Molecular simulation of steady-state evaporation and condensation in the presence of a non-condensable gas.

Using molecular dynamics simulations, we study evaporation and condensation of fluid Ar in the presence of a non-condensable Ne gas in a nanochannel. The evaporation and condensation are driven by the temperature difference, ΔT, between the evaporating and condensing liquid surfaces. The steady-state evaporation and condensation fluxes (J) are also affected by the Ne concentration, ρ, and the nanochannel length. We find that across a wide range of ΔT and ρ, J is in good agreement with the prediction from Stefan's law and from Schrage relationships. Furthermore, for ΔT less than ∼20% of the absolute average temperature, we find that both steady-state heat and mass fluxes are proportional to ΔT. This allows us to determine the interfacial resistance to the heat and mass transfer and compare it with the corresponding resistances in the gas phase. In this context, we derive an analytical expression for the effective thermal conductivity of the gas region in the nanochannel and the mass transport interfacial resistance equivalent length, i.e., the length of the nanochannel for which the resistance to the mass flow is the same as the interfacial resistance to the mass flow.