An experiment-based comparative investigation of correlations for microtube gas flow.

An experimental system was built to measure the gas (nitrogen and helium) flow characteristics in circular microchannels with diameters of 50, 20 and 5 μm. The Reynolds number of the flow was controlled in the large range of 15 to 2550. The highest Mach number could reach a magnitude of 0.625 and the highest Knudsen number was over 0.021. Four available empirical correlations were comparatively studied, in terms of the influence from compressibility and rarefaction. The accuracy of each correlation was investigated, and qualitative explanations were given according to the essence of fluid dynamics. The compressibility is found to be the dominant parameter in the experiments carried out. The results obtained by gas flow in holey optical fibres are helpful for the design of micro-scale pulse tube cryocoolers. [ABSTRACT FROM AUTHOR]