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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.

Computational Fluid Dynamics simulations are performed to investigate the effect of relevant parameters on the temperature field during the filling process of hydrogen tanks. The injector direction, the injector diameter, and the initial/ambient temperature affect the dynamics of the temperature distribution in the gas and in the tank material during the process. The development of potentially detrimental phenomena like thermal stratification and temperature inhomogeneity could occur, depending on the interactions of the effects of the 3 parameters. One of the most relevant findings is that, depending also on the other conditions, the injector direction can have a significant impact on the thermal stratification and on the critical parameters which provide an indication on the occurrence of stratification like the flow velocity at the injector exit and the Richardson number. The upward direction of the injector contributes to completely avert or at least reduce/delay the thermal gas stratification compared to injectors with a straight or downward direction.

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.

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.

A finite element analysis is performed on the heat transfer process across the tank walls to determine the temperature distributions of hydrogen storage tanks during fast filling. The accuracy of the numerical model is shown by comparison between the experimental measurements and the computed results. A sensitivity analysis of the tank wall thermal conductivity, specific heat capacity, density and heat transfer coefficient between the tank's external surface and the ambient air is carried out and the resulting effects are described. The properties of the tank's composite layer have a larger effect on the temperature history on the tank external surface than the properties of the plastic liner. The heat transfer coefficient between the tank's external surface and the environment has a negligible effect during the filling but a significant impact during the holding time. Increasing the liner thickness significantly decreases the temperature in the composite layer.

A CFD benchmark was performed within the HyIndoor project, to study hydrogen releaseand dispersion in a confined space with natural ventilation and one vent. Three experiments,performed earlier by CEA at their GAMELAN 1 m3 facility, were considered for thisbenchmark. In all three tests helium (instead of hydrogen for safety reasons) was releasedvertically upwards at 60 NL/min from a 20 mm orifice near the centre of the enclosure. Adifferent vent size was used for each test. Three HyIndoor partners (JRC, NCSRD and UU)participated in the benchmark, with three different CFD codes, (ANSYS Fluent, ADREA-HFand ANSYS CFX) and three different turbulence models respectively (transitional SST,standard k-e, dynamic Smagorinski LES). In general, good agreement was found betweenpredicted and measured helium concentrations. However, in the case of the vent with thesmallest vertical extension (vent c) all predictions overestimate the concentration at thelower part of the enclosure at steady state.

A major requirement for the filling of hydrogen tanks is the maximum gas temperature within the vessels during the process. Different filling strategies in terms of pressure and temperature of the gas injected into the cylinder and their effects on key parameters like maximum temperature, state of charge, and energy cooling demand are investigated. It is shown that pre-cooling of the gas is required but is not necessary for the whole duration of the filling. Relevant energy savings can be achieved with pre-cooling over a fraction of the time. The most convenient filling strategy from the cooling energy point of view is identified: with an almost linear pressure rise and pre-cooling in the second half of the process, a 60% reduction of the cooling energy demand is achieved compared to the case of pre-cooling for the whole filling.

The requirements regarding the refuelling process in order to prevent over-heating and over-filling significantly influence hydrogen fuelling station design and have a strong impact on potential fuelling performance. Consequently, refuelling station costs, reliability, and performance can be substantially improved by working on the way these requirements are formulated, in order to achieve shorter fuelling duration with a simpler process and less cooling. Two potential optimization opportunities were extensively investigated in the course of the EU funded HyTransfer project: (i) Application of the temperature limits to the tank material rather than to the gas inside the tank, (ii) Specification of the average delivery temperature rather than of the delivery temperature profile. Multiple research activities were carried out to this end. New models of various types were developed for predicting both the gas and material temperatures inside a vessel during filling and defueling. An experimental programme involving 82 filling and emptying tests of instrumented Type 4 and Type 3 vessels was performed for validating these models. New methods were developed and applied for determining the value of the gas-to-wall heat transfer coefficient from the temperature measurements. The balance of heat transferred from the gas to the liner and to the bosses in a type 4 vessel was reconstructed. CFD simulations were performed for analysing temperature disparities, and the thermal stratification observed in certain filling conditions reproduced. Criteria on gas injection conditions were identified for ensuring gas temperature homogeneity, a key assumption made by fuelling protocols. The temperature variations in the wall material were studied for future investigation of less conservative definitions of the maximum acceptable temperature in Hot Case situations. The effect of changing the delivery temperature profiles without changing the average delivery temperature was also analysed.

Evaluations of the performance of simplified engineering and CFD models are important to improve risk assessment tools e.g. to predict accurately releases from various types of hydrogen storages. These tools have to predict releases from a wide range of storage pressures (up to 80 MPa) and temperatures (down to 20 K), e.g. cryogenic compressed gas storage covers pressures up to 35 MPa and temperatures between 33 K and 338 K. Accurate calculations of high pressure releases require real gas EOS. This paper compares a number of EOS to predict hydrogen properties typical in different storage types. The vessel dynamics are modeled using a simplified engineering and a CFD model to evaluate the performance of various EOS to predict vessel pressures, temperatures mass flow rates and jet flame lengths. It is shown that the chosen EOS and the chosen specific heat capacity correlation are important to model accurately hydrogen releases at low temperatures.

High gas temperatures can be reached inside a hydrogen tank during the filling process because of the large pressure increase (up to 70–80 MPa) and because of the short time (∼3 min) of the process. High temperatures can potentially jeopardize the structural integrity of the storage system and one of the strategies to reduce the temperature increase is to pre-cool the hydrogen before injecting it into the tank. Computational Fluid Dynamics (CFD) tools have the capabilities of capturing the flow field and the temperature rise in the tank. The results of CFD simulations of fast filling with pre-cooling are shown and compared with experimental data to assess the accuracy of the CFD model.

The “SUpport to SAfety aNAlysis of Hydrogen and Fuel Cell Technologies (SUSANA)” project aims to support stakeholders using Computational Fluid Dynamics (CFD) for safety engineering design and assessment of FCH systems and infrastructure through the development of a model evaluation protocol. The protocol covers all aspects of safety assessment modelling using CFD, from release, through dispersion to combustion (self-ignition, fires, deflagrations, detonations, and Deflagration to Detonation Transition - DDT) and not only aims to enable users to evaluate models but to inform them of the state of the art and best practices in numerical modelling. The paper gives an overview of the SUSANA project, including the main stages of the model evaluation protocol and some results from the on-going benchmarking activities.

International audience; Hydrogen energy applications often require that systems are used indoors (e.g., industrial trucks for materials handling in a warehouse facility, fuel cells located in a room, or hydrogen stored and distributed from a gas cabinet). It may also be necessary or desirable to locate some hydrogen system components/equipment inside indoor or outdoor enclosures for security or safety reasons, to isolate them from the end-user and the public, or from weather conditions.Using of hydrogen in confined environments requires detailed assessments of hazards and associated risks, including potential risk prevention and mitigation features. The release of hydrogen can potentially lead to the accumulation of hydrogen and the formation of a flammable hydrogen-air mixture, or can result in jet-fires. Within Hyindoor European Project, carried out for the EU Fuel Cells and Hydrogen Joint Undertaking safety design guidelines and engineering tools have been developed to prevent and mitigate hazardous consequences of hydrogen release in confined environments. Three main areas are considered: Hydrogen release conditions and accumulation, vented deflagrations, jet fires and including under-ventilated flame regimes (e.g., extinguishment or oscillating flames and steady burns). Potential RCS recommendations are also identified.

A major requirement for the filling of hydrogen tanks is the maximum gas temperature within the vessels during the process. Different filling strategies in terms of pressure and temperature of the gas injected into the cylinder and their effects on key parameters like maximum temperature, state of charge, and energy cooling demand are investigated. It is shown that pre-cooling of the gas is required but is not necessary for the whole duration of the filling. Relevant energy savings can be achieved with pre-cooling over a fraction of the time. The most convenient filling strategy from the cooling energy point of view is identified: with an almost linear pressure rise and pre-cooling in the second half of the process, a 60% reduction of the cooling energy demand is achieved compared to the case of pre-cooling for the whole filling.