Computational Study on the Critical Nozzle Flow of High-Pressure Hydrogen Gas

Abstract

The critical nozzle has frequently been employed to measure the flow rate of various gases, but hydrogen gas, especially at high-pressure conditions, was not dealt with nearly as much using the critical nozzle due to treatment danger. According to experimental data obtained recently, it was reported that the discharge coefficient of hydrogen gas through the critical nozzle exceeds unity in a specific range of Reynolds numbers. No detailed explanation on such an unreasonable value was made, but it was vaguely inferred as real gas effects. For the purpose of the practical use of high-pressure hydrogen gas, systematic research is required to clarify the critical nozzle flow of high-pressure hydrogen gas. In the present study, a computational fluid dynamics method has been applied to predict the critical nozzle flow of high-pressure hydrogen gas. Several kinds of real gas equations that take into account the forces and volume of molecules of hydrogen gas were incorporated into the axisymmetric, compressible Navier-Stokes equations. A fully implicit finite volume scheme was used to numerically solve the governing equations. The computational results were validated with available experimental data. The results show that the discharge coefficient is mainly influenced by the compressibility factor and the specific heat ratio, which appear more remarkable as the inlet total pressure of hydrogen gas increases.