Rarefied gas flow through a circular orifice and short tubes

Rarefied gas flow through a circular orifice and short tubes has been investigated experimentally, and the conductance of the aperture has been calculated for Knudsen number between 0.0002 and 50. The unsteady approach was adopted, in which the decay of pressure in an upstream chamber was measured as a function of time. For flow with high pressure ratio, empirical equations of the conductance are proposed as a function of Reynolds number, or Knudsen number, and length-to-diameter ratio of the apertures.