We measured the discharge coefficients of critical nozzle using hydrogen and nitrogen gases at high-pressure and high Reynolds number (Re = 2.5 x 10^5 - 2.2 x 10^6). It were confirmed that the discharge coefficients deviated from the universal curve prescribed in ISO9300 and decreased with increase of the theoretical Reynolds number, though the values of discharge coefficient differed between two gas species. It was also confirmed that the critical nozzle flowmeter could be adopted as the transfer standard for an intercomparison by using a correction factor of the theoretical mass flow rate.
