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 ∼10−4 (hydrodynamic regime) 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.

The objective of this experimental investigation is to characterize the gas–surface interaction under different flow conditions. Therefore, the mass flow rates driven by a pressure gradient under isothermal conditions and by only a temperature gradient under constant pressure conditions are measured in the same microchannel for five different gases: helium, neon, nitrogen, argon and krypton. The pressure driven experiments are carried out in the hydrodynamic and slip flow regimes, . Using a previously developed methodology, the velocity and thermal slip coefficients are derived from the measured mass flow rates. By adopting the classical Maxwell boundary condition, the accommodation coefficients are found to be very different for both types of flows, with a significantly lower value for polyatomic nitrogen in the case of temperature gradient driven flows. An attempt to calculate the tangential momentum and normal energy accommodation coefficients in the frame of the Cercignani–Lampis model was successful only for the tangential momentum accommodation coefficient, which was found to be very close to that derived with the Maxwell model. However, it was not possible to obtain the values of the normal energy accommodation coefficient due to a lack of numerical results which connect the thermal slip and normal energy accommodation coefficients for very low values of the latter.