This work concerns the modelling of scenarios for a residential hydrogen refuelling system. Such a system is under construction within the Engineering Safe and Compact Hydrogen Energy Reserves (ESCHER) project. Non-reacting and reacting simulations are compared against experimental data before being applied to a residential garage scenario. The non-reacting simulations utilise natural ventilation, which utilises the natural buoyancy of hydrogen and vent locations to disperse flammable mixtures. This is favoured over mechanical ventilation, which could fail. The non-reacting work focuses on investigating the most suitable venting configuration for a release of hydrogen from a refuelling system located within a residential garage. Different vent configurations are examined initially before proceeding to take into account atmospheric conditions, wind, and the presence of a vehicle for the two best venting configurations. This is to determine the venting configuration that would diminish the accumulation of a flammable mixture, as well as dissipating the mixture quickest after the release has stopped. The modelling strategy utilised for this work is validated against two different sets of experimental data, prior to the investigation into residential garages. The predicted and experimental results show good agreement for the modelling procedure suggested. The reacting investigations are for both premixed and non-premixed combustion. The non-premixed combustion investigates the temperature distributions and as such the possible harm to people for such a scenario, compared against experimental data. The results show some over predictions of the temperatures. The premixed combustion investigates the potential overpressures that may occur if a homogeneous mixture was to form and ignite, within a residential garage. This work is preceded by a validation of the combustion model with the predicted results compared to data from The University of Sydney. The validation results show that the modelling strategy matches the peak overpressures accurately. The non-reacting studies show that having a lower vent opposite the release and an higher vent near the release produces the smallest flammable mixture as well as dissipating the mixture to the external surroundings quickest. The non-premixed reacting work shows good agreement with experimental results. The premixed reacting work shows that the garage would destruct with major consequences to people and surroundings. This work would be applicable to any potential usage of indoor refuelling for hydrogen vehicles, helping to determine a suitable configuration for mitigating hydrogen releases. It should be noted that all such work is geometrically dependent and as such the strategy proposed would be useful for investigating individual scenarios.

The Gaseous state of hydrogen at ambient temperature, combined with the fact that hydrogen is highly flammable, results in the requirement of more robust, high pressure storage systems that can meet modern safety standards. To develop these new safety standards and to properly predict the phenomena of hydrogen dispersion, a better understanding of the resulting flow structures and flammable regions from controlled and uncontrolled releases of hydrogen gas must be achieved. In this study the subsonic release of hydrogen was emulated using helium as a substitute working fluid. A sharp-edged orifice round turbulent jet is used to emulate releases in which leak geometry is circular. Effects of buoyancy, crossflow and adjacent surfaces were studied over a wide range of Froude numbers. The velocity fields of turbulent jets were characterized using particle image velocimetry (PIV). The mean and fluctuation velocity components were well quantified to show the effect of buoyancy due to the density difference between helium and the surrounding air. In the range of Froude numbers investigated, increasing effects of buoyancy were seen to be proportional to the reduction of the Fr number. The obtained results will serve as control reference values for further concentration measurement study and for computational fluid dynamics (CFD) validation. / Graduate

Le risque d’explosion des mélanges H2/air revêt toujours une importance cruciale pour la gestion des accidents graves dans les centrales nucléaires. Des critères expérimentaux ont été proposés dans les années 2000 par Dorofeev et al. afin de déterminer les conditions nécessaires à l’accélération de flamme et à la TDD. Ce travail de thèse a l’objectif de mieux comprendre les mécanismes d’accélération des flammes de prémélange H2/air et de fournir une solide base de données expérimentales pour la validation des codes utilisés pour les études de sûreté. Les expériences ont été menées dans un tube muni d’obstacles (taux de blocage entre 0.3 et 0.6) avec un diamètre interne de 12 cm et une longueur d’environ 5 m. Les effets de la pression initiale et de la dilution en azote sur des mélanges pauvres en H2 ont été étudiés. Les résultats montrent que la pression favorise l’accélération seulement pour les mélanges les plus réactifs et que la surpression induite par la combustion est directement proportionnelle à la pression initiale. Les interactions flamme-choc ainsi que les instabilités thermo-diffusives jouent un rôle important sur la propagation de flamme. Une nouvelle technique a été développée dans le but d’obtenir une représentation plus fine du profil de vitesse de flamme. Des mesures d’absorption IR résolues dans le temps ont été effectuées en dopant le mélange avec un alcane. Le profil de vitesse a été obtenu en mesurant la variation d’extension du gaz frais pendant l’avancement de la flamme. Enfin, des analyses préliminaires ont été menées pour la conception d’un nouveau dispositif expérimental pour l’étude des effets de la combustion sur des structures en acier inox. / Flame acceleration and explosion of hydrogen/air mixtures remain key issues for severe accident management in nuclear power plants. Empirical criteria were developed in the early 2000s by Dorofeev and colleagues providing effective tools to discern possible FA or DDT scenarios. The objectives of the present work are to better understand the mechanisms of acceleration for premixed H2/air flames and to provide a solid base of experimental data for the validation of the codes used for safety analyses. The experiments were performed in an obstacles-laden tube (blockage ratio between 0.3 and 0.6) with 120 mm internal diameter and about 5 m length. The effects of the initial pressure and the nitrogen dilution on lean H2 mixtures have been studied. The results show that pressure promote flame acceleration only for highly reactive mixtures. Moreover, the overpressure induced by the combustion is directly proportional to the initial pressure. Besides, flame-shock interactions and thermo-diffusive instabilities play an important role in flame acceleration. A new technique to track the flame position along the tube has been developed in order to obtain a finer representation of the flame velocity profile. The method consists in performing time-resolved IR absorption measurements by doping the mixture with an alkane. The velocity profile is then derivedby measuring the variation of the extension in depth of the unburnt gas along the tube axis. Finally, analyses on the effects of combustion generated loads on stainless steel structures were performed in order to provide preliminary results for the design of a new experimental device.

Development of modern safety standards for hydrogen storage infrastructure requires fundamental insight into the physics of buoyant gas dispersion into ambient air. Also, from a practical engineering stand-point, flow patterns and dispersion of gas originating from orifices in the side wall of circular pipe or storage tank need to be studied. In this thesis, novel configurations were considered to investigate the evolution of turbulent jets issuing from realistic pipeline geometries. First, the effect of jet densities and Reynolds numbers on vertical jets were investigated, as they emerged from the side wall of a circular pipe, through a round orifice. The resulting jet flow was thus issued through a curved surface from a source whose original velocity components were nearly perpendicular to the direction of the ensuing jets. Particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) techniques were employed simultaneously to provide instantaneous and time-averaged flow fields of velocity and concentration. The realistic flow arrangement resulted in an asymmetric flow pattern and a significant deflection from the vertical axis of jets. The deflection was influenced by buoyancy, where heavier gases deflected more than lighter gases. These realistic jets experienced faster velocity decay, and asymmetric jet spreading compared to round jets due to significant turbulent mixing in their near field. In addition to that, horizontal multi-component jets issuing from a round orifice on the side wall of a circular tube were also investigated experimentally by the means of simultaneous velocity and concentration measurements. A range of Reynolds numbers and gas densities were considered to study the effects of buoyancy and asymmetry on the resulting flow structure. The realistic pipeline jets were always exhibited an asymmetry structure and found to deflect about the jet's streamwise axis in the near field. In the far field, the buoyancy dominated much closer to the orifice than expected in the axisymmetric round jet due to the realistic leak geometry along with the pipeline orientation considered in this study. In general, significant differences were found between the centreline trajectory, spreading rate, and velocity decay of conventional horizontal round axisymmetric jets issuing through flat plates and the pipeline leak-representative jets considered in the present study. Finally, the dispersion of turbulent multi-component jets issuing from high-aspect-ratio slots on the side wall of a circular tube were studies experimentally by employing simultaneous PIV and PLIF techniques. Two transversal & longitudinal oblong geometries in respect to the longitudinal axes of the tube , and with an aspect ratio of 10 were considered in this study. Both horizontal and vertical orientations along with broad range of Reynolds numbers and gas densities were considered to investigate the effects of buoyancy and asymmetry on the resulting flow structure. The ensuing jets were found to deflect along the jet streamwise axis, once more, due to the realistic pipeline leak-representative configuration. It was also found that increases in aspect ratio of these realistic jets caused a reduction in the angle of deflection, jet centreline decay rates and the width growth on both velocity and scalar fields compared to their round jets counterparts, most notably in the far field. These findings indicate that conventional jets (those that are issuing through flat surfaces) assumptions are inadequate to predict gas concentration, entrainment rates and, consequently, the extent of the flammability envelope of realistic gas leaks. Thus, extreme caution is required when using conventional jet assumptions to describe the physics of a buoyant jet emitted from realistic geometries. / Graduate