Gas Flow Characteristics in MIcrotubes

Abstract

Microchannel is one of the essential components that construct various micro systems. However, it has been reported that the flow and heat transfer behavior in microchannel deviates from predictions based on the conventional assumptions generally accepted in macro scale. In this study, frictional characteristics of nitrogen (N₂), argon (Ar) and helium (He) flowing through microtubes whose diameter ranges from 5 to 100 μm have been investigated experimentally. Inlet / outlet pressure difference and volumetric flow rate were measured. In the range of Reynolds number (Re=0.03∼29.7) tested in this study, the measured friction constant was observed to take the values around 50, which is about 20% less than 64, the value regarded to be correct for macro scale tube predicted by the incompressible flow assumption. Transition from incompressible to compressible flow regimes was observed experimentally. The onset of compressibility effect was dependent on the inlet / outlet pressure difference (or the pressure ratio) as well as on the Mach number. The frictional resistance of nitrogen flow showed a Knudsen number dependence, which is in rough agreement with the first-order slip model.