Viscous slip coefficients for binary gas mixtures measured from mass flow rates through a single microtube
Résumé
The viscous slip coefficient for helium-argon binary gas mixture is extracted from
the experimental values of the mass flow rate through a microtube. The mass flow
rate is measured by the constant-volume method. The viscous slip coefficient was
obtained by identifying the measured mass flow rate through a microtube with the
corresponding analytical expression, which is a function of the Knudsen number.
The measurements were carried out in the slip flow regime where the first-order slip
boundary condition can be applied. The measured viscous slip coefficients of binary
gas mixtures exhibit a concave function of the molar ratio of the mixture, showing
a similar profile with numerical results. However, from the detailed comparison
between the measured and numerical values with the complete and incomplete
accommodation at a surface, it is inappropriate to estimate the viscous slip coeffiient
for the mixture numerically by employing separately measured tangential momentum
accommodation coefficient for each component. The time variation of the molar ratio
in the downstream chamber was measured by sampling the gas from the chamber
using the quadrupole mass spectrometer. In our measurements, it is indicated that the
volume flow rate of argon is larger than that of helium because of the difference in
the tangential momentum accommodation coefficient.