Improved Nozzle Manifold for Gas Flow Calibrations
Aaron N. Johnson, Chunhui Li, John D. Wright, Gina M. Kline, Christopher J. Crowley
We developed a new nozzle manifold that reduced the uncertainty of flow calibrations from 0.09 % to as low as 0.074 % for flows of air up to 0.84 kg/s (43 000 L/min at reference conditions of 101.325 kPa and 293.15 K). The nozzle manifold also reduces the time required to complete calibrations by a factor of 10. Twenty-one critical flow venturis (CFVs) are installed in the manifold each with a nominal throat diameter of 0.5207 cm (0.205 inch). All of the 21 CFVs are individually calibrated in dry air using NISTs recently improved 677 L PVTt standard. The CFV working standards are used in parallel to calibrate customer flow meters at flows up to 21 times the flow of a single CFV. We demonstrate that interference effects between the CFVs in the manifold are negligible and we provide an uncertainty analysis of the CFV array working standard. We used the CFV array as a transfer standard to demonstrate the metrological equivalence of NISTs 677 L and 26 m3 PVTt standards.
8th International Symposium on Fluid Flow Measurement