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Helium mass flow rates in a micro channel were measured, for a
wide Knudsen number range, in isothermal steady conditions. The
flow Knudsen numbers, considered here, cover the range from
continuum slip regime to the near free molecular regime. We used a
singe channel system involved in an experimental platform more
powerful than those previously used. The experimental errors and
uncertainties were accurately investigated and estimated. In the
continuum slip regime, it was found that the first order approach
is pertinent between 0.03-0.3 in terms of Knudsen number.
Moreover the slip coefficient was deduced by
comparing the experiments with the theoretical first order slip
continuum approach. Between 0.03-0.7 a polynomial second power
form in Knudsen number is proposed for the mass flow rate
expression. Otherwise the experimental results on the mass flow
rate were compared with theoretical values calculated from kinetic
approaches over the $0.03-50$ Knudsen range, and an overall
agreement appears through the comparison. It was also found, when
the Knudsen number increased, that the main influence of the wall
on measurements occurred first through the accommodation process
in transition regime followed, then through the aspect ratio
influence in free molecular regime. |