Dispersion of High-Pressure Hydrogen Jets in Open-Top and Indoor Environments: Effects of Leak Geometry and Pressure

Hydrogen leakage and diffusion in the operational cabin of hydrogen tube bundle containers：A CFD study

In order to reduce green house gases, hydrogen fueled vehicles are expected to be commercialized in the near future. Hydrogen is nontoxic, but it is flammable. A relatively low ignition energy can ignite a hydrogen-air mixture when the concentration of hydrogen is within a flammable range. Therefore safety concerns related to possible leakage from hydrogen fueled vehicles need to be addressed. In this study, we focus on the distribution of the lower flammability limit (LFL) of a hydrogen cloud when hydrogen is released from a fuel cell vehicle. CFD techniques, using FLUENT, are applied to the simulation of hydrogen dispersion from a parked vehicle’s tailpipe. We analyzed several hydrogen release scenarios to investigate the hydrogen cloud formation, thermal effects and transient behaviors. We also simulated the effects of the inclination of the garage ceiling and forced ventilation on hydrogen dispersion. We found that the configuration of indoor space affects the hydrogen cloud formation in certain ways. The simulation results can be further applied to define the codes, standards and recommended safety practices related to possible hydrogen leakage and the risk of ignition.

Safety evaluations on unignited high-pressure methane jets impacting a spherical obstacle

Albeit the finite resources of fossil fuel available on Earth, the world's progress in providing alternative sources of energy that can satisfy our needs has been, to a large extent, limited. The energy content (J/kg) and density (J/L) of fossil fuel sources are usually high, motivating their use in many of our daily life applications. However, because of their hazardous consequences to the environment, the search for cleaner sources of energy that could satisfy our needs and at the same time have little effect on the environment has, unfortunately, never reached, so far, a conclusion. None of the newly introduced energy sources have similar energy content and density as fossil fuel sources. For example, hydrogen looks appealing as a fuel source because of its lightweight and high energy content. However, at standard conditions, hydrogen occupies a larger volume that significantly lowers its energy density. In order to increase the energy density of hydrogen, it is crucial to store hydrogen in a liquid or compressed form. Unfortunately, hydrogen storage is considerably tricky than that for other fuel gases, which have been, to a large extent, very much comprehended with current technologies. The hydrogen gas molecules are smaller than all other gases, and they can diffuse through many materials considered airtight or impermeable to other gases. This property makes hydrogen more challenging to contain than other gases. Hydrogen leaks are dangerous in that they pose a risk of fire where they mix with air. That hydrogen is flammable and explosive over a wide range of air concentrations (4–75%) and (15–59%), respectively, at standard atmospheric temperature. Moreover, hydrogen has lower ignition energy, which is about an order of magnitude lower than that for methane and propane, and is more easily ignitable. Even an invisible spark or static electricity discharge may have enough energy to cause ignition. Therefore, hydrogen facilities need to be tight proof of hydrogen leakage. The strong possibility of hydrogen leakage can happen mainly for the following reasons. Firstly, long-term exposure of containment materials to hydrogen causes a phenomenon known as hydrogen embrittlement, resulting in cracking and hydrogen leakage. Secondly, the expected extensive usage of hydrogen in various industrial applications increases the risk of its accidental release in hydrogen infrastructures such as storage, bulk transportation, distribution, production and utilization. Hydrogen leaks may occur from loose fittings, O-ring seals, pinholes, or vents on hydrogen-containing vehicles, buildings, storage facilities or other hydrogen-based systems. The shape of the leakage source is a crucial factor and mainly affects the characterization of the leakage flow and mix in the air. Hydrogen leakage may be divided into two main classes; the first is a rapid combustible leak. The other is an incombustible slow-leak (i.e., hydrogen concentration is smaller than the lower flammability limit). Classic turbulent jet flame models can be used to model the first class of hydrogen leakage. In this review, however, we focus on the second class related to hydrogen slow-leak. This chapter will provide many typical scenarios of hydrogen leakage in air. The chapter will start with an introduction and review of the existing literature on hydrogen leakage in air. In the first part, we introduce the boundary layer approach to estimate the thickness of the hydrogen concentration layer adjacent to a ceiling wall. Both planner and axisymmetric cases of flow are considered. The impinging and far regimes are studied for each case. Moreover, vertical and horizontal hydrogen-free turbulent plumes are discussed too. Momentum-dominated and buoyancy-dominated regimes of the hydrogen plume are highlighted.

As the applications of hydrogen as a replacement for fossil fuels and energy storage increase, more concerns have been raised regarding its safe usage. Hydrogen’s extreme physical properties—its lower flammability limit (LFL), for instance—represent a challenge to simulating hydrogen leakage and, hence, mitigating accidents that occur due to such leakage. In this work, the OpenFOAM-based CFD simulation package containmentFOAM was validated by different experimental results. As in its original use, to simulate nuclear safety issues, the containmentFOAM package is capable of capturing different phenomena, like buoyant gas clouds and diffusion between gases and air. Despite being widely validated in nuclear safety, this CFD package was assessed with benchmark experiments used to validate hydrogen leakage scenarios. The validation cases were selected to cover different phenomena that occur during the hydrogen leakage—high-speed jet leakage, for example. These validation cases were the hallway with vent, FLAME, and GAMELAN experiments. From the comparison of the experimental and simulation results, we concluded that the containmentFOAM package showed good consistency with the experimental results and, hence, that it can be used to simulate actual leakage cases.

High‐pressure hydrogen leakage may undergo self‐ignition and lead to explosion even in the absence of an ignition source, making leakage detection critical for ensuring vehicle safety. A pseudo‐diameter model is introduced to convert high‐pressure hydrogen leakage into low‐pressure leakage, aiming to eliminate the impact of shockwave structures on simulation accuracy. The influence of leak location, leak hole diameter, and leak direction on hydrogen diffusion and detection is investigated in detail. Additionally, a fault database for hydrogen leakage scenarios is constructed, and the accuracy and validity of the data are verified through experiments. For sensor layout optimization, two objectives are considered: minimizing detection time and maximizing fault scenario coverage. A multiobjective optimization method based on the nondominated sorting genetic algorithm II is proposed. The results demonstrate that leak hole diameter and leak direction significantly influence hydrogen diffusion and detection time, while the impact of leak location is relatively minor. After sensor layout optimization, a 100% fault scenario coverage rate and an average fault detection time of 0.92 s can be achieved.

Semiconductor manufacturing is performed through unit processes that use various chemicals and facilities. In particular, flammable gases, such as H2, NH3, and CH4, are used, and there is a risk of explosion when such gases leak. In this study, computational fluid dynamics (CFD) simulation and a “tracer gas test” according to the SEMI (Semiconductor Equipment and Materials International) S6 Environmental, Health, and Safety Guideline for Exhaust Ventilation of Semiconductor Manufacturing Equipment specification were performed during the leakage of hydrogen, a highly flammable gas used in the etching process of a gas box in the semiconductor industry. The CFD simulation was conducted to investigate the safety of semiconductor production facilities in relation to the explosion risk. Flow analysis was performed for the interior of a gas box used in the etching process. A steady-state analysis was performed to predict the concentration range of the explosion limit in the case of continuous hydrogen gas leakage. The interior of the gas box used in the simulation was modeled, and the ventilation flow rate, which has a significant impact on the leakage gas concentration distribution, obtained from experiments was used. The lower flammability limit (LFL) value of the leaked gas was 4% based on H2, and LFL/4 (25% of the LFL) was analyzed as the explosion limit concentration according to the acceptance criteria of the SEMI S6 tracer gas test. To validate the CFD simulation, a tracer gas test was performed according to SEMI S6. A mixture of hydrogen (5%) and nitrogen (95%) was used as the tracer gas. The flow rate was controlled by a gas regulator valve and measured using an Aalborg mass flow meter. The measured concentration of the tracer gas was calculated using the equivalent release concentration, which was calculated when 100% of the hydrogen was released, and the risk was assessed by comparing it with the LFL/4 of H2.

Accelerating flammable gas cloud dissipation in hydrogen leakage during refilling hydrogen-powered vehicles via employing canopy fans

Numerical simulation of leakage jet flame hazard of high-pressure hydrogen storage bottle in open space

Leakage analysis and concentration distribution of flammable refrigerant R290 in the automobile air conditioner system

This study employed a Computational Fluid Dynamics (CFD) approach based on STAR-CD code to investigate the effect of mechanical ventilation on hydrogen gas leaks and diffusion in partially enclosed space. It is a case study of a homogenous charged compression ignition engine (HCCI) laboratory of the Mechanical Engineering Department, University College London (UCL). The 3-D modelling was based on the geometry as well as airflow designed for the test laboratory. Two turbulence models and three differencing schemes were employed on two grid refinement levels. All the differencing Schemes predicted a similar velocity profile and hydrogen concentration below 25% of the lower flammability limit (LFL) in most parts of the test laboratory. Although the predicted hydrogen mass fraction from the steady state simulation does not resolve the buoyant shape of the gas, the time-dependent solution captures the buoyant characteristic of hydrogen. It revealed that the hydrogen gas initially rises to a height 0.55cm above the exit towards the ceiling, from where it gradually diffuses in a radial pattern to a homogenous non-flammable concentration in the room. This predicted pattern of hydrogen gas dispersion is consistent with experimental data. Therefore, a small hydrogen leak of the type and at the airflow rates investigated in this study does not pose a risk of fire in most parts of the Engine Test laboratory; except in the region very close to the leak source.

Numerical investigation of the leakage and explosion scenarios in China's first liquid hydrogen refueling station

Deep learning-based hydrogen leakage localization prediction considering sensor layout optimization in hydrogen refueling stations

This study presents an optimization method of sensor layout to improve identification accuracy of indoor contaminant sources. The method integrates an index, the performance of sensor layout (PSL), with a two-step screening procedure to determine sensor layouts that have potential to achieve relatively high levels of accuracy in source identification. Using the PSL, the performance of each possible sensor layout can be predicted and evaluated, and therefore the optimization method can be performed without running a source identification model. The relationship between source identification accuracy and sensor layout was revealed through case studies in a three-dimensional office. The optimization method was demonstrated and validated by two cases in the same office, which includes optimization of sensor layouts with one and five sensors. The case studies indicate that the presented method can significantly improve source identification accuracy. The influencing factors of optimization results were discussed, and the methods to exclude unexpected optimization results were proposed.

Cuboid obstacle influence on high-pressure jet dispersion: A CFD study