Analytical methodology for calculating discharge coefficients of critical flow nozzles for high-pressure hydrogen.

Hydrogen is gaining attention as a clean energy source for the sustainable development of the global economy and mitigation of global warming. Flow rate measurements are vital for ensuring the accuracy of hydrogen transaction volumes. As a widely accepted standard for gas flow rate, critical flow nozzles are expected to fulfill this role. However, the discharge coefficient associated with the calibration tests of critical flow nozzles for high-pressure hydrogen does not align with the semi-empirical formula of ISO 9300 (ISO curve). This discrepancy has not yet been resolved. In this study, we conducted 3 D numerical simulations of the nozzle discharge coefficients for high-pressure hydrogen. Based on our simulations and experimental results from the previous study, we investigate the cause of the deviation of the discharge coefficient from the ISO curve at high pressure. We also propose a method for calculating the discharge coefficient based on real-gas effects and demonstrate that the discharge coefficient aligns with the ISO curve at high pressures. • High-pressure hydrogen flow is 3D-simulated in critical flow nozzles. • Theoretical mass flow rate of real gases is calculated in high-pressure critical nozzles. • Deviation of nozzle discharge coefficient from ISO curve under high-pressure is explained. • Calculated discharge coefficients of the proposed method match with the ISO curve. [ABSTRACT FROM AUTHOR]