Two-dimensional molecular dynamic simulations on accommodation coefficients in nanochannels with various wall configurations

Abstract

The accommodation coefficients are often utilized in slip boundary conditions to characterize gas–wall interactions. Due to the insufficient transport of momentum and energy in nanochannels, the accommodation coefficients are always less than unity and greatly influenced by temperature and surface structures. In the present paper, a statistical algorithm of the accommodation coefficients was described in molecular dynamic method. The accommodation coefficients were calculated for various wall configurations in two-dimensional nanochannels. The channels were constituted by several layers of platinum atoms, which vibrated and attached to face centered cubic (FCC) lattice sites. The results revealed that the NMAC and EAC are sensitive with the spring constant and wall atom layers. Subtle distinctions in FCC lattice and nanoscale roughness had strong effects. On FCC (1 1 1) lattice plane, the TMAC in isothermal flows was larger, while the NMAC and EAC in thermal conductions are smaller, than those on FCC (1 1 0) lattice plane. Moreover, larger roughness induced more normal momentum transferred into tangential momentum so that the NMAC decreases while the TMAC and EAC increases for larger roughness. In addition, the accommodation coefficients are also affected by rarefaction that the TMAC and EAC decrease as the Knudsen number increases.