Molecular Dynamics Study on the Effect of Adsorbed Layer on Accommodation Coefficients in Micro Gas Flow

Abstract

Tangential momentum accommodation coefficient (TMAC) is reported to be less than unity in rarefied gas flow and greatly influenced by many factors such as temperature and adsorbed layers. According to the definition, a proper statistical algorithm in NEMD method is described and verified. Adsorbed layers occur on walls due to strong gas-wall interactions and the effect on TMAC are studied in two dimensional isothermal Poiseuille flow in smooth micro-channels under the conditions of various temperatures, driving forces, and Kn. The simulation results indicate that when gas-wall interactions become stronger, TMAC increases to maximum firstly and decreases a little. Besides, the effects of temperature and Kn on TMAC are not monotonous with the existence of adsorbed layer. In addition, normal momentum accommodation coefficient (NMAC) is almost unity for isothermal flow in smooth microchannels.