Explosion venting is widely using mitigation solution in the process industry to protect indoor equipment or buildings from excessive internal pressure caused by an accidental explosion. However, vented explosion is a very complicated phenomenon to model with computational fluid dynamics (CFD). In the framework, of a French working group, the main target of this investigation is to assess the predictive capabilities of five CFD codes used by five different organizations by means of comparison with the recent experimental data. On this basis several recommendations for the CFD modelling of vented explosions are suggested.

This paper presents a comparison between two numerical approaches for the modelling of vented hydrogen deflagrations: computation fluid dynamics (CFD) simulations and empirical engineering models (EMs). The study is a part of the project ‘Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations’ (HySEA). Data from experiments conducted as part of the HySEA project are used to evaluate the CFD results and predictions from EMs. The HySEA project focusses on vented hydrogen deflagrations in containers and smaller enclosures with internal congestion representative of hydrogen applications in industry. The CFD tool FLACSHydrogen is used to simulate vented hydrogen deflagrations in 20-foot ISO containers with various obstacle configurations, and EMs for vented deflagrations are applied to the same scenarios. For the Phase 1 tests, both EM and FLACS-Hydrogen predict the maximum overpressure variation for the various configurations considered with reasonable accuracy. In general, both the EMs and the CFD tools tend to overpredict the maximum overpressures measured in the experiments. The HySEA project receives funding from the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) under grant agreement No. 671461.

In the present work, CFD simulations of a hydrogen deflagration experiment are performed. The experiment, carried out by KIT, was conducted in a 1 m3 enclosure with a square vent of 0.5 m2 located in the center of one of its walls. The enclosure was filled with homogeneous hydrogen-air mixture of 18% v/v before ignition at its back-wall. As the flame propagates away from the ignition point, unburned mixture is forced out through the vent. This mixture is ignited when the flame passes through the vent, initiating a violent external explosion which leads to a rapid increase in pressure. The work focuses on the modeling of the external explosion phenomenon. A new approach is proposed in order to predict with accuracy the strength of external explosions using Large Eddy Simulation. The new approach introduces new relations to account for the interaction between the turbulence and the flame front. CFD predictions of the pressure inside and outside the enclosure and of the flame front shape are compared against experimental measurements. The comparison indicates a much better performance of the new approach compared to the initial model.

This paper presents results from an experimental study of vented hydrogen deflagrations in 20-foot ISO containers. The scenarios investigated include 14 tests with explosion venting through the doors of the containers, and 20 tests with venting through openings in the roof. The parameters investigated include hydrogen concentration, vent area, type of venting device, and the level of congestion inside the containers. All tests involved homogeneous and initially quiescent hydrogen-air mixtures. The results demonstrate the strong effect of congestion on the maximum reduced explosion pressures, which typically is not accounted for in current standards and guidelines for explosion protection. The work is a deliverable from work package 2 (WP2) in the project “Improving hydrogen safety for energy applications through pre-normative research on vented deflagrations”, or HySEA (www.hysea.eu), which receives funding from the Fuel Cells and Hydrogen Joint Undertaking (FCH JU) under grant agreement no. 671461.

The commercial deployment of hydrogen will often involve housing portable hydrogen fuel cell power units in 20-foot or 40-foot shipping containers. Due to the unique properties of hydrogen, hazards identification and consequence analysis is essential to safe guard the installations and design measures to mitigate potential hazards. In the present study, the explosion of a premixed hydrogen-air cloud enclosed in a 20-foot container of 20’ x 8’ x 8’.6” is investigated in detail numerically. Numerical simulations have been performed using HyFOAM, a dedicated solver for vented hydrogen explosions developed in-house within the frame of the open source computational fluid dynamics (CFD) code OpenFOAM toolbox. The flame wrinkling combustion model is used for modelling turbulent deflagrations. Additional sub-models have been added to account for lean combustion properties of hydrogen-air mixtures. The predictions are validated against the recent experiments carried out by Gexcon as part of the HySEA project supported by the Fuel Cells and Hydrogen 2 Joint Undertaking (FCH 2 JU) under the Horizon 2020 Framework Programme for Research and Innovation. The effects of congestion within the containers on the generated overpressures are also investigated.

Vented deflagrations are one of the most challenging phenomenon to be replicated numerically in order to predict its resulting pressure time history. As a matter of fact a number of different phenomena can contribute to modify the burning velocity of a gas mixture undergoing a deflagration, especially when the flame velocity is considerably lower than the speed of sound. In these conditions acceleration generated by both the flow field induced by the expanding flame and from discontinuities, as the vent opening and the venting of the combustion products, affect the burning velocity and the burning behaviour of the flame. In particular the phenomena affecting the pressure time history of a deflagration after the flame front reaches the vent area, such as flame acoustic interaction and local pressure peaks, seem to be closely related to a change in the burning behaviour induced by the venting process. Flame acoustic interaction and local pressure peaks arise as a consequence of the change in the burning behaviour of the flame. This paper analyses the video recording of the flame front produced during the TP experimental campaign, performed by UNIPI in the project HySEA, to analyse qualitatively the contribution of the generated flow field in a vented deflagration in its pressure-time history.

Explosion venting is a prevention/mitigation solution widely used in the process industry to protect indoor equipment or buildings from excessive internal pressure caused by an accidental explosion. Vented explosions are widely investigated in the literature for various geometries, hydrogen/air concentrations, ignition positions, initial turbulence, etc. In real situations, the vents are normally covered by a vent panel. In the case of an indoor leakage, the hydrogen/air cloud will be stratified rather than homogeneous. Nowadays there is a lack in understanding about the vented explosion of stratified clouds and about the influence of vent cover inertia on the internal overpressure. This paper aims at shedding light on these aspects by means of experimental investigation of vented hydrogen/air deflagration using an experimental facility of 1m3 and via numerical simulations using the computational fluid dynamics (CFD) code FLACS.

Explosion venting is a method commonly used to prevent or minimize damage to an enclosure caused by an accidental explosion. An estimate of the maximum overpressure generated though explosion is an important parameter in the design of the vents. Various engineering models (Bauwens et al., 2012, Molkov and Bragin, 2015) and European (EN 14994 ) and USA standards (NFPA 68) are available to predict such overpressure. In this study, their performance is evaluated using a number of published experiments. Comparison of pressure predictions from various models have also been carried out for the recent experiments conducted by GexCon using a 20 feet ISO container. The results show that the model of Bauwens et al. (2012) predicts well for hydrogen concentration between 16% and 21% and in the presence of obstacles. The model of Molkov et al. (2015) is found to work well for hydrogen concentrations between 10% and 30% without obstacles. In the presence of obstacles, as no guidelines are given to set the coefficient for obstacles in the model, it was necessary to tune the coefficient to match the experimental data. The predictions of the formulas in NFPA 68 show a large scatter across different tests. The current version of both EN 14994 and NFPA 68 are found to have very limited range of applicability and can hardly be used for vent sizing of hydrogen-air deflagrations. Overall, the accuracy of all the engineering models was found to be limited. Some recommendations concerning their applicability will be given for vented lean-hydrogen explosion concentrations of interest to practical applications

University of Pisa performed experimental tests in a 1m3 facility, which shape and dimensions resemble a gas cabinet, for the HySEA project, founded by the Fuel Cells and Hydrogen 2 Joint Undertaking with the aim to conduct pre-normative research on vented deflagrations in real-life enclosures and containers used for hydrogen energy applications, in order to generate experimental data of high quality. The test facility, named Small Scale Enclosure (SSE), had a vent area of 0,42m2 which location could be varied, namely on the top or in front of the facility, while different types of vent were investigated. Three different ignition location were investigated as well, and the range of Hydrogen concentration ranged between 10 and 18% vol. This paper is aimed to summarize the main characteristics of the experimental campaign as well as to present its results.

Fuel cell vehicles and some compressed natural gas vehicles are equipped with carbon fiber reinforced plastic (CFRP) composite cylinders. Each of the cylinders has a pressure relief device designed to detect heat and release the internal gas to prevent the cylinder from bursting in a vehicle fire accident. Yet in some accident situations, the fire may be extinguished before the pressure relief device is activated, leaving the high-pressure fuel gas inside the fire-damaged cylinder. To handle such a cylinder safely after an accident it is necessary that the cylinder keeps a sufficient post-fire strength against its internal gas pressure, but in most cases it is difficult to accurately determine cylinder strength at the accident site. One way of solving this problem is to predetermine the post-fire burst strengths of cylinders by experiments. In this study, automotive CFRP cylinders having no pressure relief device were exposed to a fire to the verge of bursting; then after the fire was extinguished the residual burst strengths and the overall physical state of the test cylinders were examined. The results indicated that the test cylinders all recorded a residual burst strength at least twice greater than their internal gas pressure.