Authors: Sun, Jun; Li, Zhi-Xin

Source: Molecular Physics, Volume 106, Number 19, October 2008 , pp. 2325-2332(8)

Publisher: Taylor and Francis Ltd

Abstract:

The tangential momentum accommodation coefficient (TMAC), usually used in slip boundary conditions in micro-gas flows, is reported to be always less than unity and greatly influenced by temperature and the strength of gas-wall interactions. According to the definitions of accommodation coefficients, a proper statistical algorithm in non-equilibrium molecular dynamics method was described and verified. In planar Poiseuille gas flow in a smooth microchannel, the TMAC were calculated considering both the effects of temperature and gas-wall interaction. In the simulation processes, more gas molecules began to be adsorbed near walls under the condition of stronger gas-wall interaction and lower temperature. The gas adsorption resulted in a longer gas-wall interaction time so that the TMAC increased. While the gas-wall interaction became much stronger, more and more gas molecules were adsorbed to form an explicit layer above the wall. The full coverage of gas molecules on the wall prevented further adsorption; therefore the TMAC did not keep on increasing as the interaction strength continued to increase. Meanwhile, the normal momentum accommodation coefficient (NMAC) was also calculated according to the definition. In the isothermal flow, the average gas momentum normal to the wall was in complete accommodation with the wall, and the NMAC was almost unity in smooth micro channels.

Keywords: accommodation coefficient; molecular dynamics; micro gas flow; adsorption; adsorbed gas layer

Document Type: Research article

DOI: http://dx.doi.org/10.1080/00268970802452020

Affiliations: 1: Key Laboratory for Thermal Science and Power Engineering of Ministry of Education, School of Aerospace, Tsinghua University, Beijing 100084, China

Publication date: 2008-10-01

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