Experimental measurement on tangential momentum accommodation coefficient in a single microtube

The tangential momentum accommodation coefficient (TMAC) was investigated experimentally from the mass flow rate through a single microtube under the slip flow and the early part of the transition regime. The measurements were carried out by the constant-volume method under the mean Knudsen number smaller than 0.3, which is based on the mean pressure of the inlet and the outlet of the microtube, to apply the second-order slip boundary condition. To measure TMACs on various materials, quite large microtube was employed, which require the reduction in leakage. TMAC was obtained from the slip coefficient determined by the relation of the mass flow rate to the mean Knudsen number. The obtained mass flow rate was well explained by the theoretical equation. TMACs of deactivated-fused silica with argon, nitrogen, and oxygen were measured, showing the tangential momentum was not accommodated completely to the surface, and the values showed good agreement with previous studies. From the comparison between microtubes with different inner diameter, it is showed that TMAC is determined mainly by gas species and surface material.