Thermodynamic properties of hydrogen containing systems and calculation of gas critical flow factor

Sonic nozzles are emerging as crucial reference devices in the calibration of flow meters designed for hydrogen service. In this research study we aim to investigate existing equations governing the critical flow factor (C∗) for hydrogen and assess the achievable uncertainty in determining this vital property. An examination of the literature has been undertaken to target experimental measurements related to hydrogen mixtures, setting the stage for a comprehensive gap analysis. We introduced C∗ values and validated our calculations with two calibration gases: nitrogen, and methane and their standardised C∗ values. Then, the verified methodology has been utilised for generating C∗ values for hydrogen. This study concluded that the integration of precise experimental data and the utilisation of representative equations and optimised thermodynamic models is essential for enhancing the accuracy of C∗ calculations, particularly in the context of the expanding role of sonic nozzles in hydrogen flow meter calibration.