Estimation of the Uncertainty of Discharge Coefficients of Sonic Venturi Nozzles Measured by the Constant Volume Tank Method

Abstract

The paper estimates the uncertainty of discharge coefficients of sonic Venturi nozzles, which have toroidal throats complying with ISO 9300, measured at the atmospheric pressure by a constant volume tank system developed as the gas flow primary standard in Japan. Total uncertainties of the coefficients at 95% confidence level are estimated at 0.14% and 0.05%, for the smallest nozzle of Reynolds number of 0.5×10⁵ and for the largest one of 2.5×10⁵, respectively. More than half of the uncertainty of the smallest nozzle is caused by diameter measurement. Total uncertainty of mass flow rate, which is independent of the diameter measurement, is estimated at less than 0.05% for all nozzles.