Molecular Boundary Conditions and Accommodation Coefficient on A Nonequilibrium Liquid Surface

摘要

The non-equilibrium molecular dynamics (NEMD) simulations have been carried out to obtain new evidence about inverted temperature profiles. We find that the inverted temperature profile occurs due to the excess energy of the reflecting molecules without contradiction to the second law. Therefore, a new definition of the accommodation coefficient for the reflecting molecule is proposed based on the energy of the reflecting molecule under the equilibrium condition. The accommodation coefficient decreases with increasing the mass flux in the vicinity of the liquid surface and this is the reason for the inverted temperature profile. Also, a direct simulation of Monte Carlo (DSMC) method has been performed with applying the molecular boundary condition developed in the non-equilibrium molecular dynamics simulation. An inverted temperature profile is obtained because the energy of the reflecting molecule cannot reach accommodations to that of the equilibrium ones.