Abstract
IN a communication published recently on “Flow of Water through Very Narrow Channels”, Reekie and Aird1 give results obtained from measurements of the flow of both water and air through plugs of very fine powders having estimated channel widths of 0.07–0.2 micron. Although anomalous flow of water in such narrow channels was suspected, it should be pointed out that it is the flow of air which is, in fact, anomalous under such conditions. The streamline flow of a gas through a narrow capillary tube departs slightly from the normal Meyer equation due to 'slip' of the gas at the wall. While for narrow glass capillary tubes, for example, 0.05 cm. in diameter, the correction for 'slip' amounts only to about 0.1 percent, the correction assumes much bigger proportions when the diameter of the tube is comparable with the 'mean free path'(λ) of the molecules in the gas. In air at 2 atmospheres pressure, the value of λ is about 0.05 micron2 and is thus similar in magnitude to the channel widths quoted by Reekie and Aird. Under such conditions the flow of air through a capillary does not obey the ordinary laws of viscous flow. Since the effect of 'slip' is to decrease the apparent viscosity of air, this factor may account for the very high values of viscosity of water deduced by Reekie and Aird from their experiments.
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References
Reekie, J., and Aird, J., Nature, 156, 367 (1945).
Kaye and Laby, "Phys. and Chem. Constants" (2nd ed.), 33.
Rigden, P. J., J. Soc. Chem. Ind., 62, 1 (1943).
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Lea, F. M., and Nurse, R. W., J. Soc. Chem. Ind., 58, 277 (1939).
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RIGDEN, P. Flow of Fluids through Porous Plugs and the Measurement of Specific Surface. Nature 157, 268 (1946). https://doi.org/10.1038/157268a0
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DOI: https://doi.org/10.1038/157268a0
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