Mass Flow Rate Measurements in Microchannels

Mass flow rate measurements in a single silicon micro channel were carried out for various gases in isothermal steady flows. The results obtained from hydrodynamic to near free molecular regime by using a powerful experimental platform, allowed us to deduce interesting information, notably about the reflection/accommodation process at the wall. In the 0 – 0.3 Knudsen range, a continuum analytic approach was derived from NS equations, associated to first or second order slip boundary conditions. Identifying the experimental mass flow rate curves to the theoretical ones the tangential momentum accommodation coefficient (TMAC) of various gases was extracted. Over all the Knudsen range [0 – 50] the experimental results were compared with theoretical values calculated from the kinetic approaches: using variable accommodation coefficient values as fitting parameter, the theoretical curves were fitted to the experimental ones. Whatever the Knudsen range and whatever the theoretical approach, the TMAC values are found decreasing when the molecular weights of the gas increase (as long as the different gases are compared using the same approach). Moreover, the values of the various accommodation coefficients are rather close one to other but sufficiently smaller than unity to conclude that the full accommodation modelling is not satisfactory to describe the gas/wall interaction.