Discharge coefficients of square-edged orifices for measuring the flow of air

Abstract

1. Air at pressures between 1 and 13 atmospheres was passed through square-edged concentric orifices installed in long, straight pipes of 4, 6, and 8 inches nominal diameter, the three pipes being in series. At each orifice the temperature and static pressure were observed, and the fall of pressure through the orifice was measured between pairs of taps located in each of the three ways commonly adopted in commercial orifice meter practice. 2. The rate of flow was measured by throttling the air nearly to atmospheric pressure and discharging it through a flow nozzle on the end of the line. The design, calibration, and peculiarities of behavior of the nozzles are described, and the theory of this method of measurement is discussed in two appendixes. Such nozzles appear to be very satisfactory for use as primary standards. 3. The various quantities known as discharge coefficients and used in orifice meter computations are defined. 4. The experimental results are represented by equations connecting the values of the discharge coefficients with the ratio of orifice to pipe diameter and with the ratio of downstream to upstream static pressure. Tables of numerical values of discharge coefficients are also given. 5. The accuracy of the results and the limitations to their general applicability are discussed.