Performance of a Small-Sized, Critical Flowmeter Assembly

Measurement of low mass-flow rates was readily accomplished by development of two similar flowmetering assemblies. Each assembly consisted of five 0.016 to 0.070-in. diameter critical-flow nozzles and individual control valves connected between common inlet and exit manifolds. Mass-flow rates through each nozzle were determined over a range of upstream pressure and temperature. The probable deviations in the measured data are approximately ≠0.83 percent. Discharge coefficients were calculated from the calibration results using the well-known one-dimensional critical-flow equation. An average error of ≠2.5 percent in the discharge coefficient is possible because of the difficulty in determining true throat areas of these small-sized nozzles.