Calibration of Critical flow Venturi Nozzles in the transitional and turbulent boundary layer regime using hydrogen gas and air

Critical flow Venturi Nozzles (CFVNs) are expected to play a key role for metrology of gases in the future due to their affordability, reliability and flexibility. While their performance with several inert gases is well documented, there is a lack of experimental data when used with hydrogen. The objective of this work is to estimate the relevance of calibrating CFVNs with air as a surrogate gas for hydrogen, especially at transitional and turbulent flow regimes. Two nozzles with diameters 1 mm and 2 mm are calibrated with both hydrogen gas and air using a primary standard based on a pressure-Volume-Temperature-time (pVTt) system. The results show that the discharge coefficients of the CFVNs for hydrogen and air are within the expanded uncertainty of ±0.3 % (k=2) of the laboratory.