Velocity measurement in low Reynolds and low Mach number slip flow through a tube

This paper presents an experimental procedure and results of velocity measurement in the slip flow regime. The measurements are for nitrogen gas flowing at low pressure (flow Reynolds number: 4-198, Mach number: 0.05-0.12) in a conventional tube of 16 mm internal diameter. The static pressure is measured at the wall of the tube and the stagnation pressure is measured through a Pitot tube, for different mass flow rates. The velocity is estimated by applying stagnation pressure correction proposed by earlier researchers, as the Bernoulli equation cannot be applied in gas flow for Rep < 30. In the slip regime, the stagnation pressure correction is found to be a function of Reynolds number and a weak function of rarefaction. A new correlation for stagnation pressure correction is also proposed. Using this correction, velocity within ±8% with reference to the analytical solution is obtained. These results are not previously available and should help in velocity measurement ability of low Reynolds number slip flows.