Yamaguchi Hiroki, Matsuda Yu, Niimi Tomohide
Department of Micro-Nano Mechanical Science and Engineering, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi, 464-8603, Japan.
Institute of Materials and Systems for Sustainability, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi, 464-8603, Japan.
Phys Rev E. 2017 Jul;96(1-1):013116. doi: 10.1103/PhysRevE.96.013116. Epub 2017 Jul 25.
Gas-surface interaction is studied by the molecular dynamics method to investigate qualitatively characteristics of accommodation coefficients. A large number of trajectories of gas molecules colliding to and scattering from a surface are statistically analyzed to calculate the energy (thermal) accommodation coefficient (EAC) and the tangential momentum accommodation coefficient (TMAC). Considering experimental measurements of the accommodation coefficients, the incident velocities are stochastically sampled to represent a bulk condition. The accommodation coefficients for noble gases show qualitative coincidence with experimental values. To investigate characteristics of these accommodation coefficients in detail, the gas-surface interaction is parametrically studied by varying the molecular mass of gas, the gas-surface interaction strength, and the molecular size of gas, one by one. EAC increases with increasing every parameter, while TMAC increases with increasing the interaction strength, but decreases with increasing the molecular mass and the molecular size. Thus, contradictory results in experimentally measured TMAC for noble gases could result from the difference between the surface conditions employed in the measurements in the balance among the effective parameters of molecular mass, interaction strength, and molecular size, due to surface roughness and/or adsorbed molecules. The accommodation coefficients for a thermo-fluid dynamics field with a temperature difference between gas and surface and a bulk flow at the same time are also investigated.
采用分子动力学方法研究气体-表面相互作用，以定性研究适应系数的特性。对大量气体分子与表面碰撞及散射的轨迹进行统计分析，以计算能量（热）适应系数（EAC）和切向动量适应系数（TMAC）。考虑到适应系数的实验测量，对入射速度进行随机采样以代表整体条件。稀有气体的适应系数与实验值在定性上相符。为详细研究这些适应系数的特性，通过逐一改变气体的分子质量、气体-表面相互作用强度和气体的分子大小，对气体-表面相互作用进行参数研究。EAC随每个参数的增加而增加，而TMAC随相互作用强度的增加而增加，但随分子质量和分子大小的增加而减小。因此，由于表面粗糙度和/或吸附分子，在分子质量、相互作用强度和分子大小的有效参数平衡中，测量中使用的表面条件之间的差异可能导致稀有气体实验测量的TMAC出现矛盾结果。还研究了同时存在气体与表面温度差和整体流动的热流体动力学场的适应系数。
