Molecular simulation of steady-state evaporation and condensation: Validity of the Schrage relationships

The accuracy, or even the validity, of the Schrage relationships expressing the rate of evaporation and condensation in terms of local interfacial thermodynamics properties and the mass accommodation coefficient is a subject of significant discussion. In this work, we carry out molecular dynamics (MD) simulations of evaporation and condensation of fluid Ar in a nanochannel. By adjusting the temperature difference, ΔT, between the evaporating and condensing surfaces, we control the steady-state evaporation and condensation fluxes (JMD). We find that across a wide ΔT range studied, JMD is always in excellent agreement with the prediction from the exact Schrage relationships. Furthermore, if the temperature difference between the two liquid surfaces in the nanochannel is less than ∼20% of the average absolute temperature, we find that both energy and mass fluxes at the interface are proportional to ΔT. Our analysis indicates that in the case of steady-state evaporation and condensation processes, the exact Schrage relationships satisfy the conservation of mass, momentum and energy, and provides accurate predictions of the rates of the associated processes.