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In premixed H2/air explosion venting, an under-expansion jet may be caused by the pressure difference between the inside and outside of the explosion vent. Based upon the under-expansion jet, studying the structure of the under-expansion jet flame and the factors influencing its formation is essential to hydrogen safety in explosion venting. This study explored the basic characteristics of the under-expansion jet flame in premixed H2/air explosion venting, and discussed the formation of two under-expansion structures (Mach disk and diamond shock wave) of such jet flames by conducting a premixed H2/air explosion venting experiment. The influences of hydrogen fraction, explosion venting diameter, and duct length on the structure of under-expansion jet flames were evaluated. The results showed that after successful explosion venting, the under-expansion jet flame would be generated when the hydrogen fractions were 30–60 vol.%, and as the hydrogen fractions were 30–50 vol.%, the lengths of the venting duct were 30 and 50 cm. The duration of under-expansion jet flame was the longest when the hydrogen fraction was 40 vol.%. With the explosion venting diameter and hydrogen fraction increased, the spacing between under-expansion jet flame structures (S) increased. However, an increase in duct length led to the attenuation of the S. During the explosion venting, the under-expansion jet caused a pressure imbalance near the explosion vent and high-intensity convection forms on both sides of a jet, which can generate two or more explosions. Therefore, understanding the basic characteristics of under-expansion jet flame can aid the effective development of measures to prevent, mitigate, and protect against premixed H2/air explosions.

Dispersion and natural ventilation of hydrogen leaked at the floor center of a confined space are analytically and numerically studied in this contribution. Two symmetrical openings located atop two opposite walls and several sets of partition boards with varying heights, 0–1.0 m with 0.2 m increment, mounted under the ceiling were designed to examine their effects on ventilation efficiency. Without partition boards, a semi-analytical model combining a modified buoyancy ceiling jet theory and zone model was established to predict the key parameters at steady stage. The analytical predictions were compared with numerical results. 15 monitors were predesigned at an opening and the channels separated by the partition boards to collect the velocity and hydrogen concentration evolutions. The results show that the existence of the partition boards significantly promotes the ventilation efficiency by decreasing the hydrogen concentration in the confined space, constraining the flammable regime into a smaller volume, and increasing both the inflow and outflow velocities. Better ventilation efficiency is achieved by higher partition boards until a critical height after which no appreciable improvement can be gained. Applying the partition boards considerably shortens the developing stage of the dispersion process and intensifies the turbulence of outflow. Conclusions obtained in current work may benefit the natural ventilation system and building structure design for hydrogen safety in practical applications.

The development and application of hydrogen energy in power generation, automobiles, and energy storage industries are expected to effectively solve the problems of energy waste and pollution. However, because of the inherent characteristics of hydrogen, it is difficult to maintain high safety during production, transportation, storage, and utilization. Therefore, to ensure the safe and reliable utilization of hydrogen, its characteristics relevant to leakage and diffusion, ignition, and explosion must be analyzed. Through an analysis of literature, in combination with our practical survey analysis, this paper reviews the key issues concerning hydrogen safety, including hydrogen incident investigation, hydrogen leakage and diffusion, hydrogen ignition, and explosion.

An accurate prediction of the hydrogen behaviors in the accident and management process is a crucial topic for both the hydrogen safety assessment and safety analysis in the confined enclosure like the containment of the nuclear power plant (NPP). Hence, the hydrogen behaviors including the transient light gas release, stratification and dissolution in the TH22 test facility for the NPP containment are analyzed and compared using the 3-D CFD code GASFLOW-MPI in this study. In this paper, the light gas helium is adopted as a substitute for the hydrogen in the calculations in accordance with the experiment. Firstly, the detached eddy simulation (DES) turbulence model, 3-D numerical model and experiment setup are introduced. Then, the hydrogen behaviors with the GASFLOW-MPI including the light gas release, stratification and dissolution are analyzed and validated with the experiment data. In addition, the velocity profiles, light gas concentrations, dimensionless numbers and temperature distributions are evaluated for the characteristics of the hydrogen behaviors. The results indicate that the calculation results agree well with the experiment data. Foremostly, the relative errors between the calculation results and experiment data during the phase of the dissolution of the light gas cloud are within 11.9%. Meanwhile, the relative errors of the time for the complete dissolution during the phase of the dissolution of the light gas cloud are within 5.0%. For the light gas release and stratification phase, the jet flow dominates as the Froude (Fr) number exceeds 10 during the time t = 600 s–800 s. Additionally, the time averaged centerline velocity and light gas concentration after the potential core region decay with a slop of 1/z which coincide with the theoretical jet limit. Lastly, the light gas concentrations and temperature distributions in all three phases are captured clearly with the GAFLOW-MPI. It demonstrates that the GASFLOW-MPI can accurately described the details of the related hydrogen behaviors in the accident and management process in the confined enclosure like the NPP. This paper can provide guidance for the numerical computation of the hydrogen safety issues in the confined space.

Green and sustainable transportation has emerged as a mandatory task in alignment with climate change issues globally. In South Korea, fuel cell hydrogen vehicles (FCEVs) are considered to be an alternative to manage the global climate change paradigm and for local fine dust problems. However, low public acceptance is the greatest barrier to the growth of FCEVs and the hydrogen economy. To address this issue, this article discusses possible strategies for enhancing public acceptance of H2 stations using SWOT-AHP methodology and an additional focused group interview. As a result, the strength factor was the highest 1st class priority factor. In the 2nd class, the SO and ST strategies are highly recommended for enhancing public acceptance of H2 infrastructure. This article concludes with practical policy suggestions and alternatives, highlighting the importance of active research and development for hydrogen safety and the need for government-driven support.

Guidance on Sensor Placement was identified as the top research priority for hydrogen sensors at the 2018 HySafe Research Priority Workshop on hydrogen safety in the category Mitigation, Sensors, Hazard Prevention, and Risk Reduction. This paper discusses the initial steps (Phase 1) to develop such guidance for mechanically ventilated enclosures. This work was initiated as an international collaborative effort to respond to emerging market needs related to the design and deployment equipment for hydrogen infrastructure that is often installed in individual equipment cabinets or ventilated enclosures. The ultimate objective of this effort is to develop guidance for an optimal sensor placement such that, when integrated into a facility design and operation, will allow earlier detection at lower levels of incipient leaks, leading to significant hazard reduction. Reliable and consistent early warning of hydrogen leaks will allow for the risk mitigation by reducing or even eliminating the probability of escalation of small leaks into large and uncontrolled events. To address this issue, a study of a real-world mechanically ventilated enclosure containing GH2 equipment was conducted, where CFD modeling of the hydrogen dispersion (performed by AVT and UQTR, and independently by the JRC) was validated by the NREL Sensor laboratory using a Hydrogen Wide Area Monitor (HyWAM) consisting of a 10-point gas and temperature measurement analyzer. In the release test, helium was used as a hydrogen surrogate. Expansion of indoor releases to other larger facilities (including parking structures, vehicle maintenance facilities and potentially tunnels) and incorporation into QRA tools, such as HyRAM is planned for Phase 2. It is anticipated that results of this work will be used to inform national and international standards such as NFPA 2 Hydrogen Technologies Code, Canadian Hydrogen Installation Code (CHIC) and relevant ISO/TC 197 and CEN documents.

Hydrogen energy is expanding world-widely in recent years, while hydrogen safety issues have drawn considerable attention. It is widely accepted that accidental hydrogen release in an open-air environment will disperse quickly, hence not causing significant hydrogen hazards. A hydrogen hazard is more likely to occur when hydrogen is accidentally released in a confined place, i.e. parking garages and tunnels. Prediction the main accident process, including the hydrogen release, dispersion, and combustion, is important for hydrogen safety assessment, and ensuring the safety installations during accidents. Hence, a postulated accident scenario induced by the operation of Thermal Pressure Relief Device in a tunnel is analysed for hydrogen fuel cell vehicles with GASFLOW-MPI in this study. GASFLOW-MPI is a well validated parallel CFD code focusing on the transport, combustion, and detonation of hydrogen. It solves compressible Navier-Stokes equations with a powerful all-speed Arbitrary-Lagrangian-Eulerian (ALE) method; hence can cover both the non-compressible flow during the hydrogen release and dispersion phases, and the compressible flow during deflagration and detonation. In this study, a 3D model of real-scaled tunnel is modelled, firstly. Then the hydrogen dispersion in the tunnel is calculated to evaluate the risk of Flame acceleration and the Deflagration-Detonation Transient (DDT). The case with jet fire is analysed with assuming that the hydrogen is ignited right after being injected forming a jet fire in the tunnel, the consequence of this case is limited considering the small hydrogen inventory. The detonation in the tunnel is calculated by assuming a strong ignition at the top of the tunnel at an unfavourable time and location. The pressure loads are calculated to evaluate the consequence of the hazard. The analysis shows that the GASFLOW-MPI is applicable at a widely range for tunnel accidents, meanwhile, the safety issues related to tunnel accidents is worthy further study considering the complexity of tunnels.

The Australian Capital Territory (ACT) has legislated and aims to be net zero emissions by 2045. Such ambitious targets have implications for the contribution of hydrogen and its storage in gas distribution networks Therefore, we need to understand now the impacts on the gas distribution network of the transition to 100% hydrogen. Assessment of the viability of decarbonising the ACT gas network will be partly based on the cost of reusing the gas network for the safe and reliable distribution of hydrogen. That task requires each element of the natural gas safety management system to be evaluated. This article describes the construction of a test facility in Canberra, Australia used to identify issues raised by 100% hydrogen use in the medium pressure distribution network, consisting of nylon and polyethylene (PE) as a means of identifying measures necessary to ensure ongoing validity of the network's regulatory safety case. Evoenergy (the ACT's gas distribution company) have constructed a Test Facility, incorporating an electrolyser, a gas supply pressure reduction and mixing skid a replica gas network and a domestic installation with gas appliances. Jointly with Australian National University (ANU) and Canberra Institute of Technology (CIT) the Company has commenced a program of “bench testing”, initially with 100% hydrogen to identify gaps in the safety case specifically focusing on the materials, work practices and safety systems in the ACT. The facility is designed to assess: • Materials in use including aged network materials and components • Construction and installation techniques both greenfield and live gas work • Purging and filling techniques • Leak detection both underground and above ground • Emergency response and make safe techniques • Issues associated with use of hydrogen in light commercial and domestic appliances. To educate and train: • Technicians and gas fitters on infrastructure installation and management • Emergency response services on responding to hydrogen related emergencies in a network environment; and • manage public perceptions of hydrogen in a network environment. Australia has an enviable safety record for the safe and reliable transport, distribution and use of natural gas. The ACT natural gas network owned and operated by Evoenergy is one of the newest in Australia and has leveraged off the best materials and practices in Australia to build its network. The paper addresses major safety issues relating to the production/storage, distribution and consumer end use of hydrogen injected into existing gas distribution networks. The analysis is guided by the Safety Management System. The Hydrogen Testing Facility described in the paper provide tools for evaluation of hydrogen safety matters in the ACT and Australia-wide. Testing to date has confirmed that polyethylene and nylon pipe and their respective jointing techniques can contain 100% hydrogen at pressures used for the distribution of natural gas. Testing has also confirmed that current installation work practices on polyethylene and nylon pipe and joints are suitable for hydrogen service. This finding is subject to variation attributable to staff training and skill levels and further testing has been programmed as outlined in this paper. Testing of gas isolation by clamping and simulated repair on the hydrogen network has established that standard natural gas isolation techniques work with 100% hydrogen at natural gas pressures.

The main objective of this work is to apply Large Eddy Simulation (LES) on hydrogen subsonic round jets in order to evaluate modelling strategies and to provide guidelines for similar applications. The ADREA-HF code and the experiments conducted by Sandia National Laboratories are used for that purpose. These experiments are very suitable for LES studies because turbulent fluctuations have been measured which is something rare in hydrogen experiments. Hydrogen is released vertically from a small orifice of 1.91 mm diameter into stagnant environment. Three experimental cases are simulated with different Reynolds number at the release area, namely 885, 1360 and 2384. Hydrogen mass fraction and velocity mean values and fluctuations are compared against the experimental data. Several grid resolutions are used to assess the effect on the results, using mainly the Smagorinsky subgrid scale model. In the lowest Reynolds number case, an Implicit LES code, used independently from a different scientific group, is also tested. In this case, the performance of the RNG-LES subgrid scale model of the ADREA-HF code is also examined. Additionally, the effect of Smagorinsky constant and of the Van Driest correction is evaluated. The amount of the resolved turbulence and of the velocity spectra are presented. Finally, the effect of the release modelling is discussed. The analysis shows that even a coarse discretization of the release area can give acceptable results for hydrogen safety engineering applications. However, dense grids are required for the more accurate prediction of the turbulent characteristics. The two LES codes gave similar results and the overall agreement with the experiment was satisfactory.

There have been reports of ignition of high-pressure hydrogen during its sudden release for unexplained reasons and ignition mechanism still need to be further investigated. In this paper, mechanism of spontaneous ignition of high-pressure hydrogen during its sudden release into the L-shaped tube is investigated. LES, EDC model, 10-step like opening process of burst disk and 18-step detailed hydrogen combustion mechanism are employed. Three cases with burst pressures of 2.16, 6.21, and 9.10 MPa are simulated. It is found that shock wave is strongly reflected after it hits the tube corner wall, forming a reflected-shock-affected region and an energy conversion region with higher temperature, greater pressure and lower velocity. Afterwards, the reflected shock wave moving forward is reflected several times by the tube wall until it disappears and oblique shock is generated. After the hydrogen/air mixture enters the corner, it extends downstream along inner wall and separated from the main hydrogen/air mixture. The reflected shock wave moving backward interacts with the expansion waves and increases the temperature and pressure again, but spontaneous ignition cannot be initiated. Three mechanisms of spontaneous ignition of high-pressure hydrogen in the L-shaped tube are proposed eventually. The results reproduce the experimental spontaneous ignition conditions and positions, indicating that the numerical models can be applied as a tool for hydrogen safety engineering.

By necessity hydrogen-powered vehicles will be parked in covered and underground car parks. This has implications for the safety of life and property, and the development of regulations, codes and standards governing passenger vehicles and car parks. This study utilises Computational Fluid Dynamics (CFD) to investigate unignited hydrogen release and dispersion from 700 bar onboard storage in a naturally ventilated covered car park. The impact of leak diameter and angle of leak direction on the formation of the flammable cloud and the implications for vehicle passengers, first responders and car park ventilation are discussed. A typical car park with dimensions LxWxH = 30 × 28.6 × 2.6 m with two opposing vents based on the British Standard (BS 7346–7:2013) was considered. Releases through three different Thermally Activated Pressure Relief Devices (TPRD) with diameters of 3.34, 2.00 and 0.50 mm were compared, to understand the gas dispersion, specifically the dynamics of envelope formation for 1%, 2% and 4% vol of hydrogen. Concentrations in the vicinity of the vehicle and of the vents were of particular interest. It was shown how blowdown through a TPRD diameter of 3.34 mm leads to the formation of a flammable cloud throughout the majority of the car park space in less than 20 s. However, such a flammable envelope was not observed to the same extent for a TPRD diameter of 2 mm and the flammable envelope is negligible for a 0.5 mm diameter TPRD. A release through a 2 mm TPRD diameter resulted in concentrations of 1% hydrogen along the length of the car park ceiling within 20 s, which should activate hydrogen sensors, in contrast an upward release through a 0.5 mm diameter led to concentrations of 1% reaching a very limited area of the ceiling. Downward TPRD release angles of 0°, 30° and 45° were considered, and while an angle of 30° and 45° directed the hydrogen away from the car body, a downward release at 0° briefly surrounded the car doors and passenger escape routes with a flammable cloud. The study highlights the importance of release angle and demonstrates that a TPRD diameter of 0.5 mm is safer for the particular scenario considered. Larger diameter TPRDs have previously been shown to be unacceptable from a pressure peaking perspective and this study questions their use safety in a naturally ventilated covered car park.

Development of nuclear energy and hydrogen energy both as renewable energy open up a vast range of prospects. The scheme for hydrogen generation station in nuclear power plant has been carried out in china. However, Nuclear Energy is expected to encourage a safety culture that prevents serious accidents while dispersion of hydrogen from a container produces a risk of combustion. The dispersion and behavior of hydrogen production plant attached with nuclear power plant are still poorly understood. In this paper, a dispersion of hydrogen model is established and is calculated under two typical condition with corrected ideal gas state equation. The flammability of hydrogen after dispersion is studied. The range of flammability of dispersion of hydrogen production plant with different pressures, positions and temperatures is obtained. This work could contribute to the marginal hydrogen safety design for hydrogen production station and lay the foundation for the establishment of a safe distance standard that it's necessary to prevent hydrogen explosion.

The hydrogen safety issue is spotlighted as the hydrogen process is extended. For this reason, we studied catalysts for H2 oxidation at room temperature to ensure hydrogen safety. Catalysts were prepared by different preparation methods and compared to evaluate the role of Pt and Pd in Pt–Pd/TiO2 catalysts. The catalytic activity was significantly enhanced when activity metal size was small and it was exposed to catalyst surface to a high Pd ratio. For the 0.1%Pt-0.9%Pd/TiO2 catalyst, high hydrogen conversion of 90% was obtained under the condition of 0.5% hydrogen injection. To understand the correlation between activity and characteristics of catalyst, the physicochemical characteristics of the various catalysts were investigated by X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation and reduction (TPOR) and Field Emission-Transmission Electron Microscope (FE-TEM) analysis. From these analysis, it was found that Pt served the role of highly dispersion of active metal (Pt–Pd) and as with increasing Pd ratio of active metal, hydrogen activity was increased, which indicates that hydrogen oxidation had proceeded on the Pd site. Finally, the valence state of the Pd influenced hydrogen oxidation activity of Pt–Pd/TiO2, which increased with increasing ratio of Pd0/PdTotal.

The paper discusses the results of an experimental study on combustion development in a large volume filled with ultra-lean hydrogen-air mixture under terrestrial gravity conditions. For the first ...

Computational fluid dynamics (CFD) methods were used to analyze hydrogen leakage in a semi-closed ventilation facility. The goal of the research was to apply numerical simulations to verify hydrogen distribution in the semi-closed space using the commercial STAR-CCM + code and to compare the simulation results with experimental results. Experiments were conducted in a container with the dimensions 12.11 m × 2.39 m × 2.34 m. The experimental facility represents part of an underground mining tunnel. In the study, different combinations of hydrogen release pressure and leak orifice size were considered. The efficiency of forced ventilation in semi-closed spaces was also investigated. The hydrogen distribution in the ventilation facility was studied through experimental investigation and confirmed by CFD simulation. Our numerical results could be useful in the analysis of safety issues in semi-closed ventilation facilities, such as in mining tunnels.

The nomograms for graphical calculation of hazard distances and zones from a blast wave generated by a stand-alone (stationary) and an onboard (under-vehicle) high-pressure hydrogen tank ruptures in a fire are presented. The nomograms can be used by first responders, hydrogen safety engineers and other stakeholders to determine hazard distances and zones based on a blast wave strength characterised by both overpressure and impulse. The nomograms were built using the validated physical model of a blast wave decay published by the authors and accounting for the contribution of combustion into the blast wave strength. Two types of nomograms are developed: one for on-site use by the first responders, and another for design of hydrogen systems and infrastructure by hydrogen safety engineers. The paper underlines the importance of international regulatory activities to unify harm to people and damage to buildings criteria across different countries.

Hydrogen energy is one of the most promising candidates for clean and renewable energy in the coming future. Under the commission of safety study in hydrogen application, storage and transportation, CFD code analysis is always an important component in the engineering design workflow. Among the three stages of CFD analysis, the solver part has been well studied in the past two decades. However, the pre-processing and post-processing parts demand further study. The meshing process can be an important factor on the convergence speed and simulation reliability in hydrogen CFD study, which makes Cartesian mesh as an important choice in hydrogen safety codes However, traditional meshing process relies heavily on hand-based input card manipulation, which is inefficient and prone to human's improper manipulation. With the recent developments in codes like GASFLOW-MPI and FLACS, new functions have been added, which provide automatic mesh generation directly from the CAD geometry. In this work, the algorithm on automatic mesh generation will be further studied, which is more robust on the defective CAD geometries. In addition, application of the new evolving Virtual Reality technology will be implemented on the post-processing of the simulation result, which provides a better view in a real 3D environment. In the application part, three cases on a leaking hydrogen tank, a steam generator and a single car garage will be studied with regards to the validation of the new mesh generation approach. Finally, the Virtual Reality (VR) rendering performance will be studied based on the leaking hydrogen distribution in the single car garage. The work shows that the winding number based approach is an efficient and robust solution for the mesh generation of hydrogen CFD codes, and VR technology is a powerful tool for hydrogen safety simulation result rendering.

Correct use of Computational Fluid Dynamics (CFD) tools is essential in order to have confidence in the results. A comprehensive set of Best Practice Guidelines (BPG) in numerical simulations for Fuel Cells and Hydrogen applications has been one of the main outputs of the SUSANA project. These BPG focus on the practical needs of engineers in consultancies and industry undertaking CFD simulations or evaluating CFD simulation results in support of hazard/risk assessments of hydrogen facilities, as well as on the needs of regulatory authorities. This contribution presents a summary of the BPG document. All crucial aspects of numerical simulations are addressed, such as selection of the physical models, domain design, meshing, boundary conditions and selection of numerical parameters. BPG cover all hydrogen safety relative phenomena, i.e. release and dispersion, ignition, jet fire, deflagration and detonation. A series of CFD benchmarking exercises are also presented serving as examples of appropriate modelling strategies.

Thermal hazards from an under-expanded (900 bar) hydrogen jet fire have been numerically investigated. The simulation results have been compared with the flame length and radiative heat flux measured for the horizontal jet fire experiment conducted at INERIS. The release blowdown characteristics have been modelled using the volumetric source as an expanded implementation of the notional nozzle concept. The CFD study employs the realizable k-e model for turbulence and the Eddy Dissipation Concept for combustion. Radiation has been taken into account through the Discrete Ordinates (DO) model. The results demonstrated good agreement with the experimental flame length. Performance of the model shall be improved to reproduce the radiative properties dynamics during the first stage of the release (time

This work takes place in the context of potential hazards in the use of hydrogen in fuel cells. The present article describes comparisons between PIV measurements performed on a two vented cavity with an helium injection and Large Eddy Simulation of the same configuration. A two vented cavity is chosen because a quasi state is reached rapidly and it facilitates both CFD calculations by reducing the CPU costs and also enables statistical treatment of the data, the temporal averaging being possible at steady state. At the same time, this configuration is close to fuel cell designs, except for the set-up reduced size. We also describe the experimental set-up and the care which has to be taken to produce Particle Image Velocimetry velocity fields. The final goal of the paper is to validate a L.E.S approach as a good replacement to experiments, since access to both velocity and concentration fields is required to improve existing simplified models. Indeed, most of the 2 vents models rely on simplified assumptions such as a constant entrainment coefficient, a bi-layer formation which is not always the case in real situations.

The energy transition is not something that awaits us in the next decade. On the contrary, it is a process in which we are already deeply enrolled. The main step towards the creation of a carbon-neutral society is the implementation of renewable energy sources (RES) as replacements for fossil fuels. Given the intermittency of RES, energy storage has an essential role to play in this transition. Hydrogen technology with its many advances was recognized to be the most promising choice. As multiple hydrogen applications were researched relatively recently, the current development of its technology is not yet on the large-scale implementation level. With the increasing number of studies and initiated projects, the utilization of hydrogen's immense ecological potential is to be expected in the next few decades. New innovative solutions of hydrogen technology that includes hydrogen production, storage, distribution, and usage, are permeating all industry sectors. In a rapidly changing world, technological advances bring forth public discussions, that are a deciding factor whether society will be able to adapt and accept those new contributions or reject them. Currently, hydrogen is the best associated with fuel cell electric vehicles which emit only water vapour and warm air, producing no harmful tailpipe emissions. As various scientists are stressing the gravity of climate change effects that are reaching the physical environment, ecosystems, and humanity in general, concern for the future is becoming the main global topic. Consequently, governments are implementing new sustainable policies that promote RES as a substitute for fossil fuels. Increasing progress in hydrogen technology instigated nations worldwide to incorporate hydrogen in their energy legislations and national development plans, which resulted in numerous national hydrogen strategies. This work shows the progress of hydrogen taking its place as a key factor of the future green energy society. It reviews recent developments of hydrogen technologies, their social, industrial, and environmental standing, as well as the stage of transitioning economies of both advanced and beginner countries. An example of the ongoing energy transition is Croatia, which is in the process of implementing a hydrogen strategy with the ambition to be able to one day equally participates in the rapidly emerging hydrogen market.

This paper describes validation of the computational fluid dynamics tool FLACS-Hydrogen. The validation study focuses on concentration and pressure data from vented deflagration experiments performed in 20-foot shipping containers as part of the project Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations (HySEA), funded by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU). The paper presents results for tests involving inhomogeneous hydrogen-air clouds generated from realistic releases performed during the HySEA project. For both experiments and simulations, the peak overpressures obtained for the stratified mixtures are higher than those measured for lean homogeneous mixtures with the same amount of hydrogen. Using an in-house version of FLACS-Hydrogen with the numerical solver Flacs3 and improved physics models results in significantly improved predictions of the peak overpressures, compared to the predictions by the standard Flacs2 solver. The paper includes suggestions for further improvements to the model system. acceptedVersion

Various anion-exchange membranes (AEMs) were studied in the electrolysis cell using the non-precious metal-based catalysts showing the good potential of selected AEMs in low-cost water electrolysis application. The 0.1–1 M potassium hydroxide electrolyte is applied for high performance electrolysis process, whereas the usage of pure water leads to the significant AEM resistance increase. The post mortem MEA analysis, using SEM is performed to study the structure and morphology of catalyst layers transferred from the electrodes prepared by catalyst coated substrate approach. The importance of the catalyst layer–membrane interface and the binder used to bond the catalyst layer is discussed. AEM electrolysis safety aspect in terms of the hydrogen crossover through the 28 μm thin A-201 membrane is studied. The linear dependency of the permeated hydrogen flux on current density is shown. Hydrogen content in the anode outlet gas is less enough to ensure high safety of the AEM electrolysis technology in the operating currents range.

This work focuses on the overpressures arising from the rapid ignited release of hydrogen in an enclosure, specifically the peak in overpressure that may result in the initial period of the release, dependent on the level of ventilation. Two volumes are considered: a 1 m3 laboratory scale enclosure for which experimental data exists, and a real scale residential garage. Various vent configurations are considered for each scenario for leak rates typical of those from a fuel cell (laboratory scale enclosure) and from onboard hydrogen storage tanks through a thermally activated pressure relief device (TPRD) in the garage-like enclosure. A validation study has been performed for the laboratory scale enclosure and the modelling approach which gives optimum results has been identified. The influence of heat transfer on the pressure peak has been highlighted, particularly, the importance of radiation in predicting the pressure peak. The validated modelling approach has been applied to a range of experiments and garage scenarios. Both the laboratory and real scale simulations demonstrate the complex relationship between vent size and release rate and indicate the significant overpressures that can result through pressure peaking following an ignited release in an enclosure. The magnitude of the pressure peak as a result of an ignited release has been found to be two orders of magnitude greater than that for the corresponding unignited release. The work indicates that TPRDs currently available for hydrogen-powered vehicles may result in a dangerous situation for the specific scenario considered which should be accounted for in regulations, codes and standards. The application of this work extends beyond TPRDs and is relevant where there is a rapid, ignited release of hydrogen in an enclosure with ventilation.

The topic of hydrogen safety assessment has been focused by many researchers. The overpressure evaluation of vapor cloud explosion (VCE), is an important issue for both designing and evaluating on chemical plants, as well as buildings. Unknown flame radius history limits the original acoustic approximation model's application. The objective of this work is to develop an achievable model for hydrogen/air deflagration assessment in engineering applications, and the model should have high computational efficiency. A tentative scheme that starts from flame/piston speed history solving was adopted, and the flame/piston radius and acceleration history will be obtained subsequently. Thus, the overpressure history for far field could be gotten based on the acoustic approximation model. A simplified scheme was employed for the region inside the flame cloud. The model proposed in this paper could be solved in several seconds, because there are no differential equations but only algebraic equations. The model was verified by hydrogen/air deflagration tests from small scale to large scale. Compared with the experimental data, the model appeared well agreements in the medium and large scale cases. In the small scale cases, the model obtained acceptable solutions.

This paper presents an analysis of vacuum insulation failure in an automotive cryogenic pressure vessel (also known as cryo-compressed vessel) storing hydrogen. Vacuum insulation failure increases heat transfer into cryogenic vessels by about a factor of 100, potentially leading to rapid pressurization and venting of the cryogen to avoid exceeding maximum allowable working pressure (MAWP). Hydrogen release to the environment may be dangerous, especially if the vehicle is located in a closed space (e.g. a garage or tunnel) at the moment of insulation failure. We therefore consider utilization of the hydrogen in the vehicle fuel cell and dissipation of the electricity by operating vehicle accessories or electric resistances as an alternative to releasing hydrogen to the environment. We consider two strategies: initiating hydrogen extraction immediately after vacuum insulation failure or waiting until maximum operating pressure is reached before extraction. The results indicate that cryogenic pressure vessels have thermodynamic advantages that enable slowing down hydrogen release to moderate levels that can be consumed in the fuel cell and dissipated in vehicle accessories supplemented by electric resistances, even in the worst case when the insulation fails at the moment when the vessel stores hydrogen near its maximum density (70 g/L at 300 bar). The two proposed strategies are therefore feasible, and the best alternative can be chosen based on economic and/or implementation constraints.

This paper presents the results of a survey of university students' knowledge and perception of hydrogen technology by interviewing 93 Finnish energy engineering students before and after a learning assignment that deals with hydrogen technology. The results suggest that both the students' knowledge and perception on hydrogen technology improve between the pre-assignment and the post-assignment surveys. The largest changes take place in their knowledge on hydrogen safety and their willingness to acquire a home hydrogen system. Correlations between the students' level of knowledge in various topics and their opinions strengthened and multiplied during the assignment. Some unexpected connections between knowledge and opinions occurred. The study argues that system-level approaches should be integrated in hydrogen energy education instead of just teaching chemical reactions or hydrogen technologies. Both radical and conventional problem settings that challenge the students to both think in a creative manner and to keep the realism should be cultivated.

Hydrogen is a highly flammable gas and accidental release in confined space can pose serious combustion hazards. Numerical studies are required to assess the formation of flammable hydrogen cloud within confined spaces. In the present study, numerical investigations on the release of helium and hydrogen gases as high-velocity jets and their subsequent distribution inside an unventilated cylindrical enclosure (AIHMS facility) has been carried out as a first step towards numerical studies on hydrogen distribution in confined spaces for safety assessments. Experimental data for jet release of helium at volume Richardson number 0.1 and subsequent distribution has been used as benchmark data. Sensitivity studies on the influence of grid sizes, time-steps and turbulence models are performed. The performance of the validated numerical model is evaluated using statistical performance parameters. Similarity relations are used to determine input parameters for hydrogen jet for corresponding experimental data with helium jets. Finally, the mixing and flammability aspects of hydrogen distribution inside the enclosure are studied using four numerical indices that quantify mixing and deflagration potential of a distribution. It is concluded that the helium experiments can be used for validation of numerical models for hydrogen safety studies and any one of the similarity relationships, viz., equal buoyancy, equal volumetric flow, or equal concentration can be used for assessing the behaviour of hydrogen release and distribution within confined spaces.

During the filling of hydrogen tanks high temperatures can be generated inside the vessel because of the gas compression while during the emptying low temperatures can be reached because of the gas expansion. The design temperature range goes from −40 °C to 85 °C. Temperatures outside that range could affect the mechanical properties of the tank materials. CFD analyses of the filling and emptying processes have been performed in the HyTransfer project. To assess the accuracy of the CFD model the simulation results have been compared with new experimental data for different filling and emptying strategies. The comparison between experiments and simulations is shown for the temperatures of the gas inside the tank, for the temperatures at the interface between the liner and the composite material, and for the temperatures on the external surface of the vessel.

HyRAM is a methodology and accompanying software toolkit being developed to provide a platform for integration of state-of-the-art, validated science and engineering models and data relevant to hydrogen safety. The HyRAM software toolkit establishes a standard methodology for conducting quantitative risk assessment (QRA) and consequence analysis relevant to assessing the safety of hydrogen fueling and storage infrastructure. The HyRAM toolkit integrates fast-running deterministic and probabilistic models for quantifying risk of accident scenarios, for predicting physical effects, and for characterizing the impact of hydrogen hazards (thermal effects from jet fires, thermal and pressure effects from deflagrations and detonations in enclosures). HyRAM 1.0 incorporates generic probabilities for equipment failures for nine types of hydrogen system components, generic probabilities for hydrogen ignition, and probabilistic models for the impact of heat flux and pressure on humans and structures. These are combined with fast-running, computationally and experimentally validated models of hydrogen release and flame behavior. HyRAM can be extended in scope via user-contributed models and data. The QRA approach in HyRAM can be used for multiple types of analyses, including codes and standards development, code compliance, safety basis development, and facility safety planning. This manuscript discusses the current status and vision for HyRAM.

The objective of the presented work is to develop an efficient and validated approach based on a multi-dimensional computational fluid dynamics (CFD) code for predicting turbulent gaseous dispersion, conjugated heat and mass transfer, multi-phase flow, and combustion of hydrogen mixtures. Applications of interest are accident scenarios relevant to nuclear power plant safety, renewable energy systems involved in hydrogen transport, hydrogen storage, facilities operating with hydrogen, as well as conventional large scale energy systems involving combustible gases. All model development is conducted within the framework of the high-performance scientific computing software GASFLOW-Multi-Physics-Integration (MPI). GASFLOW-MPI is the advanced parallel version of the GASFLOW sequential code with many newly developed and validated models and features. The code provides reliability, robustness and excellent parallel scalability in predicting all-speed flow-fields associated with hydrogen safety, including distribution, turbulent combustion and detonation. In the meanwhile, it has been well verified and validated by many international blind and open benchmarks. The recently developed combustion models in GASFLOW-MPI code are based on the transport equation of a reaction progress variable. The sources consist of turbulence dominated and chemistry kinetics dominated terms. Models have been implemented to compute the turbulent burning velocity for the turbulence controlled combustion rate. One-step and two-step models are included to obtain the chemical kinetics controlled reaction rate. These models, combined with the efficient and verified all-speed solver of the GASFLOW-MPI code, can be used for simulations of deflagration, detonation and the important transition processes like flame acceleration (FA) and deflagration-to-detonation-transition (DDT), without additional need for expert judgment and intervention. It should be noted that the major goal is to develop a reliable and efficient numerical tool for large-scale engineering analysis, instead of resolving the extremely complex physical phenomena and detailed chemistry kinetics on microscopic scales. During the course of this development, new verification and validation studies were completed for phenomena relevant to hydrogen-fueled combustion, such as shock wave capturing, premixed and non-premixed turbulent combustion with convective, conductive and radiation heat losses, detonation of unconfined hydrogen–air mixtures, and confined detonation waves in tubes. Excellent agreements between test data and model predictions support the predictive capabilities of the combustion models in GASFLOW-MPI code. In Part II of the paper, the newly developed CFD methodology has been successfully applied to a first analysis of hydrogen distribution and explosion in the Fukushi Daicchi Unit 1 accident. The major advantage of GASFLOW-MPI code is the all-speed capability of simulating laminar and turbulent distribution processes, slow deflagration, transition to fast hydrogen combustion modes including detonation, within a single scientific software framework without the need of transforming data between different solvers or codes. Since the code can model the detailed heat transfer mechanisms, including convective heat transfer, thermal radiation, steam condensation and heat conduction, the effects of heat losses on hydrogen deflagrations or detonations can also be taken into account. Consequently, the code provides more accurate and reliable mechanical and thermal loads to the confining structures, compared to the overly conservative results from numerical simulations with the adiabatic assumptions. Predictions of flame acceleration mechanisms associated with turbulent flames and flow obstacles, as well as DDT modeling and their comparisons to available data will be presented in future papers. A structural analysis module will be further developed. The ultimate goal is to expand the GASFLOW-MPI code into an integral high-performance multi-physics simulation tool to cover the entire spectrum of phenomena involved in the mechanistic hydrogen safety analysis of large scale industrial facilities.

Hydrogen safety issue in a ventilation system of a generic nuclear containment is studied. In accidental scenarios, a large amount of burnable gas mixture of hydrogen with certain amount of oxygen is released into the containment. In case of high containment pressure, the combustible mixture is further ventilated into the chambers and the piping of the containment ventilation system. The burnable even potentially detonable gas mixture could pose a risk to the structures of the system once being ignited unexpectedly. Therefore the main goal of the study is to apply the computational fluid dynamics (CFD) computer code – GASFLOW, to analyze the distribution of the hydrogen in the ventilation system, and to find how sensitive the mixture is to detonation in different scenarios. The CFD simulations manifest that a ventilation fan with sustained power supply can extinguish the hydrogen risk effectively. However in case of station blackout with loss of power supply to the fan, hydrogen/oxygen mixture could be accumulated in the ventilation system. A further study proves that steam injection could degrade the sensitivity of the hydrogen mixture significantly.

A two-layer, reduced order model of high pressure hydrogen jets was developed 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. The flow after the Mach disk is subsonic while the flow around the Mach disk is supersonic with a significant amount of entrained air. This flow structure significantly affects the hydrogen concentration profiles downstream. The predictions of this model are compared to previous experimental data for high pressure hydrogen jets up to 20 MPa and to notional nozzle models and CFD models for pressures up to 35 MPa using ideal gas properties. The results show that this reduced order model gives better predictions of the mole fraction distributions than previous models for highly underexpanded jets. The predicted locations of the 4% lower flammability limit also show that the two-layer model much more accurately predicts the measured locations than the notional nozzle models. The comparisons also show that the CFD model always underpredicts the measured mole fraction concentrations.

Safety is of paramount importance in all facets of the research, development, demonstration and deployment work of the U.S. Department of Energy's (DOE) Fuel Cell Technologies Program. The Safety, Codes and Standards sub-program (SCS design and manufacturing; deployment and operations. The work of the Hydrogen Safety Panel highlights new knowledge and the insights gained through interaction with project teams. Various means of collaboration to enhance the value of the program's safety knowledge tools and training resources are illustrated and the direction of future initiatives to reinforce the commitment to safety is discussed.

Passive auto-catalytic recombiners (PARs) have the potential to be used in the future for the removal of accidentally released hydrogen inside confined areas. PARs could be operated both as stand-alone or backup safety devices, e.g. in case of active ventilation failure. Recently, computational fluid dynamics (CFD) simulations have been performed in order to demonstrate the principal performance of a PAR during a postulated hydrogen release inside a car garage. This fundamental study has now been extended towards a variation of several boundary conditions including PAR location, hydrogen release scenario, and active venting operation. The goal of this enhanced study is to investigate the sensitivity of the PAR operational behavior for changing boundary conditions, and to support the identification of a suitable PAR positioning strategy. For the simulation of PAR operation, the in-house code REKO-DIREKT has been implemented in the CFD code ANSYS-CFX 15. In a first step, the vertical position of the PAR and the thermal boundary conditions of the garage walls have been modified. In a subsequent step, different hydrogen release modes have been simulated, which result either in a hydrogen-rich layer underneath the ceiling or in a homogeneous hydrogen distribution inside the garage. Furthermore, the interaction of active venting and PAR operation has been investigated. As a result of this parameter study, the optimum PAR location was identified to be close underneath the garage ceiling. In case of active venting failure, the PAR efficiently reduces the flammable gas volume (hydrogen concentration > 4 vol.%) for both stratified and homogeneous distribution. However, the simulations indicate that the simultaneous operation of active venting and PAR may in some cases reduce the overall efficiency of hydrogen removal. Consequently, a well-matched arrangement of both safety systems is required in order to optimize the overall efficiency. The presented CFD-based approach is an appropriate tool to support the assessment of the efficiency of PAR application for plant design and safety considerations with regard to the use of hydrogen in confined areas.

Hydrogen fuels are being deployed around the world as an alternative to traditional petrol and battery technologies. As with all fuels, regulations, codes and standards are a necessary component of the safe deployment of hydrogen technologies. There has been a focused effort in the international hydrogen community to develop codes and standards based on strong scientific principles to accommodate the relatively rapid deployment of hydrogen-energy systems. The need for science-based codes and standards has revealed the need to advance our scientific understanding of hydrogen in engineering environments. This brief review describes research and development activities with emphasis on scientific advances that have aided the advancement of hydrogen regulations, codes and standards for hydrogen technologies in four key areas: (1) the physics of high-pressure hydrogen releases (called hydrogen behavior); (2) quantitative risk assessment; (3) hydrogen compatibility of materials; and (4) hydrogen fuel quality.

Compressed hydrogen storage is currently widely used in fuel cell vehicles due to its simplicity in tank structure and refueling process. For safety reason, the final gas temperature in the hydrogen tank during vehicle refueling must be maintained under a certain limit, e.g., 85 °C. Many experiments have been performed to find the relations between the final gas temperature in the hydrogen tank and refueling conditions. The analytical solution of the hydrogen temperature in the tank can be obtained from the simplified thermodynamic model of a compressed hydrogen storage tank, and it serves as function formula to fit experimental temperatures. From the analytical solution, the final hydrogen temperature can be expressed as a weighted average form of initial temperature, inflow temperature and ambient temperature inspired by the rule of mixtures. The weighted factors are related to other refueling parameters, such as initial mass, initial pressure, refueling time, refueling mass rate, average pressure ramp rate (APRR), final mass, final pressure, etc. The function formula coming from the analytical solution of the thermodynamic model is more meaningful physically and more efficient mathematically in fitting experimental temperatures. The simple uniform formula, inspired by the concept of the rule of mixture and its weighted factors obtained from the analytical solution of lumped parameter thermodynamics model, is representatively used to fit the experimental and simulated results in publication. Estimation of final hydrogen temperature from refueling parameters based on the rule of mixtures is simple and practical for controlling the maximum temperature and for ensuring hydrogen safety during fast filling process.

This paper describes a series of explosion experiments in inhomogeneous hydrogen air clouds in a standard 20′ ISO container. Test parameter variations included nozzle configuration, jet direction, reservoir back pressure, time of ignition after release and degree of obstacles. The paper presents the experimental setup, resulting pressure records and high speed videos. The explosion pressures from the experiments without obstacles were in the range of 0.4–7 kPa. In the experiments with obstacles the gas exploded more violently producing pressures in order of 100 kPa.

A properly trained first responder community is critical to the successful introduction of hydrogen fuel cell applications and their transformation in how we use energy. Providing resources with accurate information and current knowledge is essential to the delivery of effective hydrogen and fuel cell-related first responder training. The California Fuel Cell Partnership and the Pacific Northwest National Laboratory have over 15 years of experience in developing and delivering hydrogen safety-related first responder training materials and programs. A National Hydrogen and Fuel Cell Emergency Response Training Resource was recently released ( http://h2tools.org/fr/nt/ ). This training resource serves the delivery of a variety of training regimens. Associated materials are adaptable for different training formats, ranging from high-level overview presentations to more comprehensive classroom training. This paper presents what has been learned from the development and delivery of hydrogen safety-related first responder training programs (online, classroom, hands-on) by the respective organizations. The collaborative strategy being developed for enhancing training materials and methods for greater accessibility based on stakeholder input will be discussed.

The core-melt in Fukushima-Daiichi Unit 1 represents a new class of severe accidents in which combustible gas from core degradation leaked from the containment into the surrounding air-filled reactor building, formed there a highly reactive gas mixture, and exploded 25 h after begin of the station black-out. Since TMI-2 hydrogen safety research and management has focussed on processes and counter-measures inside the containment but the reactor building remained unprotected against hydrogen threats. The code GASFLOW-MPI is currently under development to simulate hydrogen behaviors, including distribution and combustion, for scenarios with containment leakage. This paper describes a first analysis of the hydrogen explosion in Unit 1. It investigates gas dispersion in the reactor building, assuming a leak at the drywell head flange, shows the evolution of a stratified, inhomogeneous H 2 –O 2 –N 2 –steam mixture in the refueling bay, simulates the combustion of the reactive gas mixture, and predicts pressure loads to walls and internal structures of the reactor building. The blast wave propagated essentially sideways, which explains why all side walls were blown out and the ceiling just collapsed onto the floor of the refueling bay. The blast wave propagation into the free environment was also simulated. The over-pressure amplitudes are sufficiently high to cause damage to adjacent buildings and to injure people. The hitherto existing presumption that the blow-out panel of Unit 2 was removed by the Unit 1 explosion can be confirmed which likely prevented a hydrogen explosion in the Unit 2. GASFLOW-MPI provides validated models for the integral simulations of leakage related core-melt scenarios. Furthermore, the code contains extensively tested submodels for catalytic recombiners, igniters and burst foils, which allow design of new hydrogen risk mitigation systems for currently unprotected spaces in reactor buildings.

This paper demonstrates experimental and numerical study on spontaneous ignition of H2–N2 mixtures during high-pressure release into air through the tubes of various diameters and lengths. The mixtures included 5% and 10% (vol.) N2 addition to hydrogen being at initial pressure in range of 4.3–15.9 MPa. As a point of reference pure hydrogen release experiments were performed with use of the same experimental stand, experimental procedure and extension tubes. The results showed that N2 addition may increase the initial pressure necessary to self-ignite the mixture as much as 2.12 or 2.85 – times for 5% and 10% N2 addition, respectively. Additionally, simulations were performed with use of Cantera code (0-D) based on the ideal shock tube assumption and with the modified KIVA3V code (2-D) to establish the main factors responsible for ignition and sustained combustion during the release.

This paper introduces the 3D risk management (3DRM) concept, with particular emphasis on hydrogen installations (Hy3DRM). The 3DRM framework entails an integrated solution for risk management that combines a detailed site-specific 3D geometry model, a computational fluid dynamics (CFD) tool for simulating flow-related accident scenarios, methodology for frequency analysis and quantitative risk assessment (QRA), and state-of-the-art visualization techniques for risk communication and decision support. In order to reduce calculation time, and to cover escalating accident scenarios involving structural collapse and projectiles, the CFD-based consequence analysis can be complemented with empirical engineering models, reduced order models, or finite element analysis (FEA). The paper outlines the background for 3DRM and presents a proof-of-concept risk assessment for a hypothetical hydrogen filling station. The prototype focuses on dispersion, fire and explosion scenarios resulting from loss of containment of gaseous hydrogen. The approach adopted here combines consequence assessments obtained with the CFD tool FLACS-Hydrogen from Gexcon, and event frequencies estimated with the Hydrogen Risk Assessment Models (HyRAM) tool from Sandia, to generate 3D risk contours for explosion pressure and radiation loads. For a given population density and set of harm criteria, it is straightforward to extend the analysis to include personnel risk, as well as risk-based design such as detector optimization. The discussion outlines main challenges and inherent limitations of the 3DRM concept, as well as prospects for further development towards a fully integrated framework for risk management in organizations.

Since the Fukushima nuclear power plant accident, the nuclear safety experts devote a number of efforts to explore the potential risk of hydrogen detonation and measures for the mitigation of hydrogen safety during a severe accident in the nuclear power plant. A series of experiments have been performed to investigate the behavior of hydrogen distribution during a severe accident in the nuclear power plant. This study aims to investigate the gaseous stratification break-up phenomenon in the presence of a vertical gas fountain on the top of containment using Code_Saturne. The computed results not only analyze the flow field of the gas and the density distribution in the containment, but also measure the adequacy of Code_Saturne concerning the multi-component gas flow calculation.

International audience; In the context of hydrogen safety and explosions in hydrogen-oxygen systems, numerical simulations of laminar, premixed, hydrogen/air flames propagating freely into a spray of liquid water are carried out. The effects on the flame velocity of hydrogen/air flames of droplet size, liquid-water volume fraction, and mixture composition are numerically investigated. In particular, an effective reduction of the flame velocity is shown to occur through the influence of water spray.To complement and extend the numerical results and the only scarcely available experimental results, a “Laminar Flame Velocity under Droplet Evaporation Model” (LVDEM) based on an energy balance of the overall spray-flame system is developed and proposed. It is shown that the estimation of laminar flame velocities obtained using the LVDEM model generally agrees well with the experimental and numerical data.

This paper describes a methodology for simulating the structural response of vented enclosures during hydrogen deflagrations. The paper also summarises experimental results for the structural response of 20-foot ISO (International Organization for Standardization) containers in a series of vented hydrogen deflagration experiments. The study is part of the project Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations (HySEA). The project is funded by the Fuel Cells and Hydrogen 2 Joint Undertaking under grant agreement No 671461. The HySEA project focuses on vented hydrogen deflagrations in containers and smaller enclosures with internal congestion representative of industrial applications. The structural response modelling involves one-way coupling of pressure loads taken either directly from experiments or from simulations with the computational fluid dynamics (CFD) tool FLACS to the non-linear finite element (FE) IMPETUS Afea Solver. The performance of the FE model is evaluated for a range of experiments from the HySEA project in both small-scale enclosures and 20-foot ISO containers. The paper investigates the sensitivity of results from the FE model to the specific properties of the geometry model. The performance of FLACS is evaluated for a selected set of experiments from the HySEA project. Furthermore, the paper discusses uncertainties associated with the combined modelling approach.

University of Pisa (UNIPI) conducted a series of vented deflagration tests at B. Guerrini Laboratory. The tests were part of the experimental campaign performed by UNIPI for the European HySEA project (Hydrogen Safety for Energy Applications). Experiments included homogeneous hydrogen-air mixture contained in an about 1 m3 enclosure, called SSE (Small Scale Enclosure). The mixture concentration was variable between 10% and 18% vol. During the deflagrations, structural response was investigated by measuring the displacement of a test plate. The collected data were used to validate the FE model developed by IMPETUS Afea. In this paper experimental facility, displacement measurement system and FE model are briefly described, then comparison between experimental data and simulation results is discussed.

In this article, numerical results from a highly resolved large eddy simulations (LES) of an air-helium buoyant jet developing in a two vented cavity are presented. The simulated configuration mimics the helium-release experiment carried out at CEA Saclay in the framework of security assessment of indoor used hydrogen-based systems. The height of the enclosure was chosen so that a laminar-turbulent transition occurs approximately at the middle of the upstream direction. An exterior region, of different spatial dimensions, has been modeled in the computational domain in order to move the boundary conditions away from the vent surface and to approach the natural inlet/outlet conditions. A sensitivity analysis regarding the size of the exterior region is presented to define the minimum horizontal extension so that the flow inside the cavity is not furthermore influenced by bigger computational domains. We observe mainly that applying an ambient equilibrium-hydrostatic pressure outlet condition directly on the surface of the vent reduces the volume of the air inflow, and thus predicts larger helium mass inside the cavity, in contrary with the cases where an exterior region is considered. A qualification analysis shows that the sub-grid scale model plays a small role in the calculations and thus implies that the LES predictions approach the direct numerical simulation (DNS) solution. Analysis carried out on the time-averaged helium field depicts a concentration regime that is not classical in such configurations and thus the theoretical model used in safety pre-calculations can not be served.

The use of hydrogen gas as a fuel to be burned or to be spent in a hydrogen fuel cell vehicle is increasing. While hydrogen is a renewable and clean energy career, the safety aspects associated with it is still a key issue. Hydrogen has a wide flammability range and needs less energy to be ignited, compared to other common fuels. Experiments on hydrogen safety are not an economic and safe approach; hydrogen is a very dangerous substance, and expensive to test in a safe environment. Use of Computational Fluid Dynamics (CFDs) is an alternative method to predict the behaviour of hydrogen gas after an accidental release. Providing the concentration profile for the area of concern, and the ability to investigate different parameters such as ventilation, obstacles’ configurations and ignition sources are the advantages of using CFDs codes for the safe design of hydrogen stations and hydrogen fuel cell vehicles. In the current study, a CFD based approach is proposed to evaluate the dispersion behaviour of hydrogen gas after a release from a hydrogen fuel cell car in an enclosed area. The fuel concentration profile in the compartment is produced, considering different ventilation conditions. Mitigation measures are also applied to improve the ventilation condition and decrease the fuel concentration below the flammable level. The proposed approach is useful for better design of safety measures to prevent consequent accidents or minimise the harmful impacts during an accident.

The effect of an adjacent surface on the lower flammability limit cloud extents of high pressure horizontal and vertical unignited jets of both hydrogen and methane is studied using Computational Fluid Dynamics (CFD) simulations performed with FLACS Hydrogen. Two jet directions (horizontal and vertical) and two surface positions (horizontal or ground, vertical or side wall) were studied: horizontal jets along a horizontal surface, vertical and horizontal jets along a vertical surface or side wall. Results for constant flow rate through a 6.35 mm round leak orifice from 101 bar, 251 bar, 401 bar, 551 bar and 701 bar compressed gas systems are presented. The effect of the surface on the flammable extents is studied systematically by positioning the jet exit release at various distances from the surface ranging from 0.029 m to 10 m. Free jets simulations were performed for comparison purposes. Our results were quantified by establishing engineering correlations that could be used to predict the flammable extent of hydrogen and methane jet releases in the presence of surfaces. These correlations were validated using experiments conducted for horizontal hydrogen jets in the vicinity of horizontal surfaces, carried out at the facilities of Defence Research and Development Canada (DRDC) in Val-Belair, Quebec.

The ability to predict the concentration of hydrogen in a partially confined space is significant to the safe use of hydrogen-related products such as fuel cell vehicles. Hydrogen release and subsequent dispersion are frequently investigated using commercially-available computational fluid dynamic (CFD) models once those are calibrated with available experimental data. Due to the explosion safety concerns of using hydrogen, accidental scenarios are often replicated with helium as a hydrogen simulant in experiments. Currently, there is no validated, theoretical analogy to correlate the helium data in order to predict the spatial and temporal distribution of hydrogen in the enclosure. The aim of this paper is to assess different theoretical relationships for the similarity between hydrogen and helium leakage in an enclosure. Experiments were first carried out to obtain measured data with helium leakage in a set of scenarios and to validate the present CFD model. Three methods, namely equal volumetric flow rate, equal buoyancy and a newly proposed correlation derived from equal concentration, were employed to determine the equivalent hydrogen release rate, using which the validated CFD model was then used, with the physical property values for hydrogen, to stimulate hydrogen dispersion as compared to that of helium. The accuracy of these different methods at different stage of release and location is discussed. The present result thus provides a guide when using helium experiment to validate hydrogen simulation in different scenarios, which is of importance to the investigation of hydrogen safety.