Numerical Study on Characteristics of High-Pressure Hydrogen Gas Flow in a Critical Nozzle

Critical nozzles have been proposed as one of flowmeters that can be used under high-pressure conditions with stagnation point pressure of 70 MPa or more and can measure with high accuracy. The critical nozzle is a device for measurement of the mass flow using the flow-choking phenomenon at the nozzle throat and the theoretical mass flow rate is a function of the temperature, the pressure, ratio of specific heats at the stagnation point upstream of the nozzle and the diameter of the nozzle throat. In such a flow in the critical nozzle, the coefficient of discharge approaches 1 as Reynolds number increases. In previous studies, it has been shown experimentally and theoretically that the discharge coefficient of hydrogen gas in the region of high Reynolds number decreases with an increase of pressure at the stagnation point upstream of the nozzle. The objective in the present research is to investigate the effect of the stagnation temperature on the discharge coefficient of the critical nozzle.