AN EXPERIMENTAL INVESTIGATION OF THE ABSOLUTE VISCOSITY OF ARGON AND DRY AIR RELATIVE TO THE ABSOLUTE VISCOSITY OF NITROGEN USING LAMINAR FLOWMETERS

摘要

The performance characteristics of such gas flow-metering devices as orifice plates, sonic and subsonic nozzles and venturi tubes are usually conveyed in terms of a discharge coefficient vs. Reynolds number. In contrast to liquid flow-metering applications, where the necessary fluid properties may be measured directly, values of the absolute viscosity of a gas used in the computation of Reynolds number must be taken from the literature. Owing to the complexity of the experimental apparatus required for the determination of gas viscosities, seldom are the uncertainties of the reported viscosity values better than one percent. In connection with the above-mentioned flow-meters, a one percent uncertainty in viscosity is certainly tolerable, since even a three percent error in viscosity (Reynolds number) will not significantly affect the value of the discharge coefficient. Another type of flow-meter which is now widely used for high-accuracy gas flow measurement is the laminar flow-meter. The operation of this device is such that any error in the derived viscosity of the flowing gas will produce an error of equal magnitude in the reported flow-rate. A precise knowledge of gas viscosities is therefore prerequisite to the use of laminar flow-meters, particularly when attempting to transfer calibration data from one gas to another. Results of an extensive experimental program in which a number of laminar flow-meters were calibrated with nitrogen, argon and dry air have led to the development of equations for the viscosity of argon and dry air relative to that of nitrogen. The equations presented allow for the complete transferability of laminar flow-meter calibration data for one gas to either of the other two with errors not greater than + 0.16 percent at the 95% Confidence Level for operating line pressures near one atmosphere absolute and temperatures in the range of 50 to 90°F (283 to 305 K).