The mass flow rate through microchannels with rectangular cross section is measured for the wide Knudsen number range (0.0025–26.2) in isothermal steady conditions. The experimental technique called ‘Constant Volume Method’ is used for the measurements. This method consists of measuring the small pressure variations in the tanks upstream and downstream of the microchannel. The measurements of the mass flow rate are carried out for three gases (Helium, Nitrogen and Argon). The microchannel internal surfaces are covered with a thin layer of gold with mean roughness Ra = 0.87nm (RMS). The continuum approach (Navier-Stokes equations) with first order velocity slip boundary condition was used in the slip regime (Knudsen number varies from 0.0025 to 0.1) to obtain the experimental velocity slip and accommodation coefficients associated to the Maxwell kinetic boundary condition. In the transitional and near free molecular regimes the linearized kinetic BGK model was used to calculate numerically the mass flow rate. From the comparison of the numerical and measured values of the mass flow rate the accommodation coefficient was also deduced.

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