Non-equilibrium evaporation: 1D benchmark problem for single gas

Abstract

Evaporation is one of the most effective processes for heat transfer enhancement in the confined spaces. The development of efficient tools for modeling of evaporation processes requires a clear understanding of the applicability of existing approaches. The planar evaporation of a monoatomic gas at low and arbitrary evaporation speed (Mach number lower than 0.5) is simulated using the numerical solution of the S-model kinetic equation. These results are compared with the Molecular Dynamics simulations available from literature and our simulations performed using the LAMMPS tools. The S-model kinetic equation is shown to be an excellent time-effective model to simulate the structure inside and beyond from the Knudsen layer. It is also shown that non-linear Moment Method of the solution of Boltzmann equation gives the results in good agreement with the S-model and Molecular Dynamics data and it can be used for engineering applications when the heat flux in the gas phase above the Knudsen layer is negligible. The useful tool for evaporation rate calculation based on analytical Moment Method formulas is provided as well. It is shown that the well-known Schrage expression considerably overestimate the evaporation rates with the evaporation coefficients calculated using Molecular Dynamics approach. The provided results could be used as the benchmark data to test evaporation models.