Gas flow through microtubes with different internal surface coatings

An experimental setup based on the constant volume technique is developed to measure the mass flow rate through microtubes under isothermal stationary flow conditions. Four different working gases (helium, nitrogen, argon, and carbon dioxide), and two surface materials (stainless steel and Sulfinert) are considered. The Knudsen number calculated for the experimental conditions varies from similar to 10(-4) (hydrodynamic regime) to similar to 5 (transitional regime). In the reduced range (10(-4) - 0.1) corresponding to the hydrodynamic and slip regimes, an approach based on the analytical solution of the Stokes equation subjected to a first order velocity slip boundary condition is used. The velocity slip coefficient and the tangential momentum accommodation coefficient are extracted from the experimental data of the mass flow rate using their analytical expressions. The results are summarized in the tables representing the accommodation coefficients for the corresponding gas-surface material combinations. The influence of the molecular mass on the tangential momentum accommodation coefficient is discussed. In addition, an original technique is proposed to extract the accommodation coefficient in the whole experimentally available range (10(-4) - 5) of the gas rarefaction. The accommodation coefficients obtained using this technique are close to those found in the slip regime. (C) 2014 American Vacuum Society.