As there are no published data verifying the theoretical Fanning friction factors for streamline flow of air at low absolute pressures, an investigation was made of the pressure drops in 6 to 18-in-diam pipe lines in which room-temperature air was flowing at absolute pressures varying from 50 microns Hg to 1 mm Hg. The large number of pressure-drop readings taken at various rates of flow permits developing friction-factor curves for this type of flow. These are presented in this paper.

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