Friction resistance for gas flow in smooth microtubes

A new tube-cutting method was used to measure the pressure and Mach number distribution along a microtube of 108.3 um. Experiments were also performed concerning the average Fanning friction factors of five kinds of microtube s whose diameters range from 80.0 to 166.6 mu m. It is found that the press ure distribution in a microtube becomes nonlinear at a high Mach number and the product of measured average Fanning friction factors (C) over bar(t) a nd Reynolds number Re is higher than 16. Numerical results show that the ga s compressibility leads to a variation of the velocity profile from parabol ic, and results in a large velocity gradient at the tube inner wall surface . The transition from laminar to turbulence in microtubes also occurs at Re approximate to 2 300, and the phenomenon of early transition is not observ ed in the experiments.