Masanori Shiro

Effect of surface material and roughness on conductance of channel between parallel disks at molecular flow

The effect of surface material and roughness on the conductance of a channel at molecular flow was measured for N2, Ar, He, and H2. The experimental results were compared with the results of Monte Carlo calculations. The channel consisted of two parallel disks with different surfaces including polished stainless steel (SS), roughly polished SS, quartz, Ti, Cu, Al, alumina with smooth surface, alumina with rough surface, Au coating, Pt coating, and diamondlike carbon (DLC) coating. The conductances of the experimental channel depended on the slope of the surface roughness, rather than the arithmetic surface roughness (Ra) or the material. In the case of smooth surfaces, such as polished SS, quartz, and DLC coating, the experimental results for N2, Ar, and H2 show good agreement with the calculation, assuming diffuse reflection. The momentum accommodation coefficients on these surfaces for N2, Ar, and H2 were estimated to be in the range from 0.98 to 1.00, based on the assumption that specular reflection wa...