The present work studies the friction characteristics of gaseous
slip flow in microtubes. The reduced diameter of microtubes has significant
influences on the flow. The degree of influence depends on
the Knudsen number. If the Knudsen number is in the range of 10−3 to
0.1, the fluid can be assumed to be a continuum but a slip boundary
condition at the tube wall has to be employed to account for the incomplete
tangential momentum and energy exchanges between the gas molecules
and the wall. Although slip flow in microtubes can be investigated
by solving numerically the compressible Navier-Stokes equations,
the hyperbolic-parabolic character of the equations makes it very
inefficient. The very large length to diameter ratio of microtube flows
suggests that they can be predicted accurately as well as efficiently by
solving the compressible boundary-layer equations. The parabolic character
of the boundary-layer equations renders the present method a very
efficient and accurate tool in studying slip flows. The results confirm
the findings of earlier investigators that the product of f . Re is smaller
for laminar microtube flows than that predicted by the conventional
theory when the flow is in the slip region.
Relation:
Journal of the Chinese Institute of Engineers=中國工程學刊 24(5), pp.641-647
