Dispersion Of Unintended Subsonic And Supersonic Hydrogen Releases From Hydrogen Storage Systems

Energy shortages and environment pollution are among the most important problems worldwide. As a clean and renewable energy carrier, hydrogen is expected to be one of the most promising alternative solutions to the energy and environmental problems in the near future. However, the safety issues in hydrogen production,transport and storage have to be thoroughly addressed before commercialization of hydrogen energy to give authorities confidence and to eliminate the public fear of using hydrogen. Accurate knowledge of the dispersion characteristics of unintended hydrogen releases in the atmosphere is essential to developing good standards and codes for hydrogen safety. The paper presents a series of experimental, theoretical and numerical studies of unintended hydrogen releases.A planar laser Rayleigh scattering(PLRS) system was used in this study to quantify the concentration fields during low pressure, subsonic hydrogen and helium releases and high pressure, supersonic hydrogen releases. A second experimental setup used mini-katharometers to measure the helium concentrations during high pressure,supersonic helium releases. The hydrogen and helium concentration measurements for the low pressure, subsonic jets and the high pressure, underexpanded jets showed that the axial mass fraction follows the canonical hyperbolic decay law in both cases and that the radial mass fraction profile is Gaussian. Thus, the self-preservation behavior of the jet concentration is verified for both subsonic and supersonic, underexpanded jets.The shock structures of high pressure underexpanded hydrogen jets were imaged by an inline Schlieren system. The location and diameter of the Mach disk as well as the boundary layer thickness were all found to scale linearly with the nozzle diameter and the square root of the pressure ratio.The classical integral model used to model low pressure releases contains many empirical coefficients that have historically been based on early experimental data for water and air jets, which are not appropriate for modeling hydrogen jets. In this study,the empirical coefficients are refined using the hydrogen concentration measurements to develop models appropriate for hydrogen jets. A model for high pressure underexpanded hydrogen jets was then developed by combining the proper notionalnozzle model and the improved integral model. The model is then shown to be able to accurately predict hydrogen jet concentration fields by comparison with experimental data.Numerical models were also used to simulate the subsonic jets and the high pressure, underexpanded hydrogen jets for various conditions. The simulation results with sufficiently refined computational meshes and appropriate turbulent models are in good agreement with the experimental data. However, the shock region makes the numerical calculations very unstable and slow for highly underexpanded jets. Thus, a two-layer, reduced order model was developed for high pressure hydrogen jets using empirical equations for the flow in the shock region and the mass, momentum and energy conservation equations, which includes partitioning of the flow between the central core jet region leading to the Mach disk and the supersonic slip region around the core. Simplified simulations using the two-layer model are much more efficient than the complete simulations and more accurate than previous notional nozzle models.