Impact d'une onde de choc sur une structure cylindrique

Dans un contexte de sécurité industrielle, il est important de connaître les caractéristiques de l'onde de souffle consécutive à une explosion d'origine quelconque, lorsque cette explosion se produit à proximité d'un bâtiment, ceci dans le but de protéger les installations et le personnel. Pour cela, une approche expérimentale est envisagée. L'objectif du présent travail est de définir des modèles de chargements appliqués à une structure de forme cylindrique rencontrée dans l'industrie et susceptible de subir une explosion à proximité des murs mais pas à leur contact. Cet objectif est poursuivi de manière originale à travers la réalisation d'essais d'explosions de gaz menés en laboratoire. Un certain nombre de lois sont exprimées et validées par les expériences. Des simulations numériques sont réalisées en parallèle à l'aide du code Autodyn, et une bonne corrélation avec les résultats expérimentaux est obtenue

Investigation on the thermal degradation and kinetic parameters of innovative insulation materials using TGA-MS

Thermogravimetric analyzer coupled to a mass spectrometer (TGA-MS) was used to study the thermochemical behavior of eight samples. Two varieties of straw (wheat and barley) and two others of binder (lime and plaster) have employed to design four composites. These composites can be considered as innovative insulation materials for buildings. The thermal degradation of the different specimens was studied from a temperature of 50 to 1000ºC using increased temperature of 20ºC/min. This thermal degradation is an important element to evaluate the fire behavior and predict the evolution of smoke emitted during an accidental fire for building application. Using MS analyzer, the ion currents evolutions of 16 molecule groups (shared by a m/z ratio) were followed as functions of temperature. TG curves show that the thermal decomposition of composite samples is more complex (3-4 mass loss steps) than the one of the basic materials (1-2 mass loss stages) and seems to be mostly affected by the binder nature. The highest amount of gas in pyrolysis products is associated to m/z=28 ratio and presents more than two thirds of the total quantity. The kinetic parameters were evaluated for the more important mass loss of each sample and their values are in the ranges of 8.29-64.86 kJ/mol, 0.4-3.36 and 1.78 x 10^3 -1.63 x 10^7 min^-1 for respectively the activation energy, the reaction order and the pre-exponential factor.Peer ReviewedPostprint (author's final draft

Numerical Study on the Outdoor Wind Effects on Movement Smoke along a Corridor

In this chapter, a numerical investigation is presented in order to highlight the effects of outdoor wind on smoke movements along a corridor in a compartment. For this, the Computational Fluid Dynamics (CFD) code, fire dynamics simulator (FDS), was used to model the reactive flows in interaction with outdoor wind. The wind velocity is taken between 0 and 12.12 m/s, based on the experimental result data come from the work of Li et al. was performed. From numerical data, it was found that smoke stratification state in the corridor depends on Froude number (Fr) and it can be divided into three cases: stable buoyant stratification (Fr < 0.38), unstable buoyant stratification (0.38 ≤ Fr < 0.76), and failed stratification (Fr ≥ 0.76). When Fr ≥ 0.76, smoke stratification is completely disturbed and smoke occupies the entire volume of the compartment, highlighting a risk of toxicity to people. Indeed, it was observed that the velocity of the outdoor wind influences strongly the concentration of O2, CO2, CO, and visibility in the corridor and smoke exhaust. Moreover, for the input data used in the numerical modelling, the global sensitivity analysis demonstrated that the main parameters affecting the smoke temperature near the ceiling are the mass flux of fuel and the activation energy

BLEVE Fireball Effects in a Gas Industry: A Numerical Modeling Applied to the Case of an Algeria Gas Industry

This chapter presents the numerical modeling of the BLEVE (Boiling Liquid Expanding Vapor Explosion) thermal effects. The goal is to highlight the possibility to use numerical data in order to estimate the potential damage that would be caused by the BLEVE, based on quantitative risk analysis (QRA). The numerical modeling is carried out using the computational fluid dynamics (CFD) code Fire Dynamics Simulator (FDS) version 6. The BLEVE is defined as a fireball, and in this work, its source is modeled as a vertical release of hot fuel in a short time. Moreover, the fireball dynamics is based on a single-step combustion using an eddy dissipation concept (EDC) model coupled with the default large eddy simulation (LES) turbulence model. Fireball characteristics (diameter, height, heat flux and lifetime) issued from a large-scale experiment are used to demonstrate the ability of FDS to simulate the various steps of the BLEVE phenomenon from ignition up to total burnout. A comparison between BAM (Bundesanstalt für Materialforschung und –prüfung, Allemagne) experiment data and predictions highlights the ability of FDS to model BLEVE effects. From this, a numerical study of the thermal effects of BLEVE in the largest gas field in Algeria was carried out

Détermination expérimentale des émissions gazeuses de trois espèces végétales potentiellement impliquées dans les feux de forêt accélérés

La plupart des espèces végétales impliquées dans les feux de forêt produisent et émettent des composés organiques volatils (COV). Ces gaz ont des limites inférieures d’inflammabilité de l’ordre de 1 % volumique dans l’air et sont donc fortement inflammables. Les modèles physiques de propagation des feux de forêt n’intègrent pas jusqu’à présent la combustion de ces composés et l’objectif de cette étude est de fournir des données expérimentales afin d’améliorer ces modèles pour mieux prévoir et contrôler les incendies. L’accent est mis sur un phénomène particulièrement dangereux, les feux de forêts accélérés. Il a en effet été noté dans la littérature que sous certaines conditions (de topographie, d’humidité, etc.) les feux de forêt peuvent se comporter de manière surprenante, passant soudainement d’un comportement (vitesse de propagation et énergie dégagée) modéré à un comportement « explosif ». Une hypothèse qualifiée de thermochimique a été proposée pour expliquer ces phénomènes : les COV émis par les plantes (mélangés ou non avec les gaz de pyrolyse) pourraient s’accumuler près du sol en concentration suffisante pour former un prémélange inflammable avec l’air et ainsi entrainer l’accélération du feu. Il existe dans la littérature des données sur les émissions gazeuses des végétaux à température ambiante mais très peu sur les émissions en fonction de la température. Trois espèces typiques des régions méditerranéennes et correspondant à différentes hauteurs du couvert végétal sont étudiées entre 343 et 453 K : Thymus vulgaris, Rosmarinus officinalis et Pinus pinea. Les émissions sont étudiées à l’aide d’un pyrolyseur flash relié à un chromatographe en phase gazeuse couplé à un spectromètre de masse. Les résultats sont discutés et comparés à ceux de la littérature à température ambiante

On the Critical Behaviour of Exothermic Explosions in Class A Geometries

The aim of this work is to apply the homotopy perturbation method for solving the steady state equations of the exothermic decomposition of a combustible material obeying Arrhenius, Bimolecular, and Sensitised laws of reaction rates. These equations are formulated on some Class A geometries (an infinite cylinder, an infinite slab, and a sphere). We also investigate the effect of Frank-Kamenetskii parameter on bifurcation and thermal criticality by means of the Domb-Sykes graphical method

On the Critical Behaviour of Exothermic Explosions in Class A Geometries

The aim of this work is to apply the homotopy perturbation method for solving the steady state equations of the exothermic decomposition of a combustible material obeying Arrhenius, Bimolecular, and Sensitised laws of reaction rates. These equations are formulated on some Class A geometries (an infinite cylinder, an infinite slab, and a sphere). We also investigate the effect of Frank-Kamenetskii parameter on bifurcation and thermal criticality by means of the Domb-Sykes graphical method

Thermal Effects of CO2 on the NOx Formation Behavior in the CH4 Diffusion Combustion System

International audienceThe objective of this present study was to numerically investigate the quantitative thermal effects of CO2 replacement of N2 in the oxidizer side on NOx formation for CH4 diffusion combustion system established in counterflow configuration at atmospheric pressure. The mole fraction of O2 in the oxidizer was kept constant at 21%. Calculations were conducted at different stretch rates and different percentage of CO2 in the oxidizer. Calculations were also carried out with and without radiation to quantify the effects of radiation heat transfer. For this simulation, a modified CHEMKIN code and a radiation code developed by the Combustion Group of ICPET were used. Mainly due to its much higher specific heat, replacement of nitrogen in air by carbon dioxide significantly lowered the temperature of the flame, leading to much lower NO concentrations. For a specified stretch rate, there existed a maximum percentage of CO2 in the oxidizer beyond which flame extinction occur. The value of the maximum percentage of CO2 in the oxidizer decreased as the stretch rate increased. Effect of radiation heat transfer become more important as the stretch rate decreased. Replacement of N2 by CO2 in the oxidizer was an effective way to control NOx formation in CH4 diffusion flames mainly due to its thermal effect and secondly due to its chemical and radiative effects