New classes of exact solutions to nonlinear sets of equations in the theory of filtration and convective mass transfer

The definitive version can be found at www.springerlink.comNew classes of exact solutions to nonlinear sets of equations encountered in the theory of filtration and convective mass transfer of reacting media are described. Focus is placed on general first-order sets in which the chemical reaction rates depend on arbitrary functions. General solutions to some first-order systems with power-law nonlinearities are found. A set of new exact solutions with a functional separation of variables involving arbitrary functions is constructed. The results obtained are used for solving the problems of the theory of filtration of one-component and multicomponent suspensions with an arbitrary kinetics of particle accumulation.E. A. Vyazmina, P. G. Bedrikovetskii and A. D. Polyani

Identification of safety critical scenarios of hydrogen refueling stations in a multifuel context

International audienceThe MultHyFuel Project, funded by the Clean Hydrogen Partnership, aims to achieve the effective andsafe deployment of hydrogen as a carbon-neutral fuel, by developing a common strategy forimplementing Hydrogen Refueling Stations (HRS) in a multifuel context. The project hopes tocontribute to the harmonisation of existing regulations, codes and standards (RCS) by generatingpractical, theoretical and experimental data related to HRS.This paper presents how a set of safety critical scenarios have been identified from the initial preliminaryas well as detailed risk analysis of three different hydrogen refueling station configurations. To achievethis, a detailed examination of each potential hazardous phenomenon (DPh) or major accident event ator near the hydrogen dispenser was carried out. Particular attention is paid to the scenarios which couldaffect third parties external to the refueling station.The paper presents a methodology subdivided into the following steps: determination of the consequence level and likelihood of each hazardous phenomenon, the classification of major hazard scenarios for the 3 HRS configurations, specifically thosearising on the dispensing forecourt; proposal of example preventative, control and/or mitigation barriers that could potentiallyreduce the probability of occurrence and/ or consequences of safety critical scenarios, and hencereducing risks to a tolerable level or to as low as reasonably practicable

Protective walls against effects of vapor cloud fast deflagration CFD recommendations for design

International audienceProtective walls are a well-known and efficient way to mitigate overpressure effects of explosions. For detonation there are multiple published investigations concerning interactions of blast waves and walls, whereas for deflagration no well-adapted and rigorous method has been reported in the literature. This article describes the validation of a new computational fluid dynamics (CFD) modeling approach for fast deflagrations. In a first step, the vapor cloud explosion involving a fast deflagration is substituted by an equivalent vessel burst problem. The purpose of this step is to avoid reactive flow computations. In a second step, CFD is used to model the pressure propagation from the equivalent (nonreactive) vessel burst problem. After verifying the equivalence of the fast deflagration and the vessel burst problem in the first step, the ability of two CFD codes FLACS and Europlexus is examined for situations with and without barriers. Parametric analysis by means of numerical simulations is performed to investigate the efficiency of finite barriers to mitigate blast waves. Another parametric study shows how the maximum overpressure value in the shade of the barrier depends on the magnitude of the incoming overpressure wave. On this basis, several recommendations are suggested for designing protective walls. © 2017 American Institute of Chemical Engineers Process Process Saf Prog 3756–66, 2018. © 2017 American Institute of Chemical Engineer

Bifurcation structure of viscous vortex breakdown

International audienceIncompressible axisymmetric swirling flow with open boundaries is studied by means of direct numerical simulation (DNS). The effects of viscosity and external axial pressure gradient near critical swirl number are investigated. The solution branches obtained from DNS match the bifurcation diagrams from previous theoretical and numerical studies and extend their results

A new method to assess mitigation efficiency of a protective barrier against the effects of a vapor cloud explosion

Accidental gas explosions represent an ever-present hazard for process industries handling flammable gases and liquids. There is also an increasing danger of vandals and terrorists using improvised explosive devices in industrial areas neighboring highly populated residential areas. The consecutive pressure wave generation and propagation can result in unacceptable risk exposition of citizens and infrastructures. Therefore, it is necessary to define design rules of protective barriers mitigating the effect of blast wave

Detailed Assessment of Dispersion for High-Pressure H2 in Multifuel Environment

International audienceThe MultHyFuel project notably aims to produce the data missing for usable risk analysis and mitigationactivity for Hydrogen Refuelling Stations (HRS) in a multi-fuel context.In this framework, realistic releases of hydrogen that could occur in representative multi-fuel forecourtswere studied. These releases can occur inside or outside fuel dispensers and they can interact with acomplex environment notably made of parked cars and trucks. This paper is focused on the most criticalscenarios that were addressed by a sub-group through the use of Computational Fluid Dynamics (CFD)modelling. Once the corresponding source terms for hydrogen releases were known, two stages arefollowed: Model Validation – to evaluate the CFD models selected by the task partners and to evaluatetheir performance through comparison to experimental data. Realistic Release Modelling – to perform demonstration simulations of a range of criticalscenarios.The CFD models selected for the Model Validation have been tested against measured data for a set ofexperiments involving hydrogen releases. Each experiment accounts for physical features that areencountered in the realistic cases. The selected experiments include an under-expanded hydrogen jetdischarging into the open atmosphere with no obstacles or through an array of obstacles. Additionally,a very different set-up was studied with buoyancy-driven releases inside a naturally ventilated enclosure.The results of the Model Validation exercise show that the models produce acceptable solutions whencompared to measured data and give confidence in the ability of the models, and the modellers, tocapture the behaviour of the realistic releases adequately.The Realistic Release Modelling phase will provide estimation of the flammable gas cloud volume fora set of critical scenarios and will be described at the second stage

Vented explosion of hydrogen/air mixture: An intercomparison benchmark exercise

International audienceExplosion venting is a widely used mitigation solution in the process industry to protect indoor equipment or buildings from excessive internal pressure caused by accidental explosions. However, vented explosions are very complicated to model using 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 recent experimental data. On this basis several recommendations for the CFD modelling of vented explosions are suggested

Zone negligible extent: example of specific detailed risk assessment for low pressure equipment in a hydrogen refuelling station

International audienceThe MultHyFuel project aims to develop evidence-based guidelines for the safe implementation ofHydrogen Refueling Stations (HRS) in a multi-fuel context. As a part of the generation of good practiceguidelines for HRS, Hazardous Area Classification (HAC) methodologies were analyzed and applied tocase studies representing example configurations of HRS. It has been anticipated that Negligible Extent(NE) classifications might be applicable for sections of the HRS, for instance, a hydrogen generator. ANE zone requires that an ignition of a flammable cloud would result in negligible consequences. Inaddition, depending on the pressure of the system, IEC 60079-10-1:2020 establishes specificrequirements in order to classify the hazardous area as being of NE. One such requirement is that a zoneof NE shall not be applied for releases from flammable gas systems at pressures above 2000 kPag (20barg) unless a specific detailed risk assessment is documented. However, there is no definition withinthe standard as to the requirements of the specific detailed risk assessment. In this work, an example fora specific detailed risk assessment for the NE classification is presented:• Firstly, the requirements of cloud volume, dilution and background concentration for a zoneof NE classification from IEC 60079-10-1:2020 are analyzed for hydrogen releases fromequipment placed in a mechanically ventilated enclosure.• Secondly, the consequences arising from the ignition of the localized cloud are estimatedand compared to acceptable harm criteria, in order to assess if negligible consequences areobtained from the scenario.• In addition, a specific qualitative risk assessment for the ignition of the cloud in theenclosure was considered, incorporating the estimated consequences and analyzing theavailable safeguards in the example system.Recommendations for the specific detailed risk assessment are proposed for this scenario with theintention to support improved definition of the requirement in future revisions of IEC 60079-10-1