Measurement of the tangential momentum accommodation coefficient of H2 on stainless steel, extreme ultraviolet-resist, and polyimide

The tangential momentum accommodation coefficient (TMAC) of H2 on electropolished stainless steel 304, extreme ultraviolet-resist, and polyimide was determined by measuring the mass flow through a macroscopic rectangular channel (100 cm × 10 cm × 1 cm) as a function of the pressure drop in the Knudsen range Knave ≈ 0–0.6. The TMAC and Knudsen number determine the amount of velocity slip taking place at the wall at rarefied conditions. By comparing the measurements with an analytical expression for the mass flow through the channel, including the 1st order slip flow contribution to continuum, the only remaining unknown, that is, the TMAC, was extracted.