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Extended Data Analysis of Bilateral Comparisons with Air and Natural Gas up to 5 MPa



John D. Wright, Bodo Mickan, J-P Vallet, CHUNHUI LI


In 2015, the PTB, LNE-LADG, NIM and NIST performed informal bilateral comparisons using six critical venturi nozzles. The goal of the comparisons was to prove the equivalence of reference standards for gas flow using pressurized air and natural gas at pressures from 0.1 MPa to 5 MPa. The evaluation of the data utilized a function for the discharge coefficient of critical nozzles as a function of the Reynolds number and real gas characteristics. The fitting function covers both laminar and turbulent boundary layer operating ranges of a nozzle with a single equation. The summary of all results of this comparison series shows that the proposed function for the discharge coefficient can represent single measurement values within 0.1 % with a 95 % confidence level. The approach represents the results reported by participants using functions based on physical understanding of the transfer standards. The paper documents the full equivalence of all traceabilities involved in these comparisons. The comparison database includes not only measurement sets of 2015 but also measurements done by PTB in other years with the same nozzles. Hence, qualitative statements on the long term reproducibility could inform the analysis on multilateral equivalence of the participants. Linked bilateral comparisons can effectively expose discrepant labs and perhaps give insight on the long term drift of primary standards.
Proceedings Title
Conference Dates
September 26-29, 2016
Conference Location
Sydney, AT


critical flow venturi, nozzle, comparison, gas flow


Wright, J. , Mickan, B. , Vallet, J. and Li, C. (2016), Extended Data Analysis of Bilateral Comparisons with Air and Natural Gas up to 5 MPa, FLOMEKO 2016, Sydney, AT, [online], (Accessed July 15, 2024)


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Created September 28, 2016, Updated April 7, 2022