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Détermination par un code CFD de l'évolution de la puissance d'un feu en régime de sous-ventilation dans un milieu confiné et mécaniquement ventilé

Abstract : For several years, many experimental/numerical research programs have been carried out at IRSN in order to provide sufficient data on the burning process and understand the behavior of a pool fire in a confined and mechanically ventilated compartment. Several experimental tests have shown that in some cases, the oxygen concentration in the local decreases then stabilizes until fire extinction. The fuel mass loss rate is instantaneously adjusted according to the ventilation in the local, which may leads to a lower fuel consumption rate as compared to that in free atmosphere. The fire duration is then 2 to 3 times greater than that obtained in free atmosphere, which may damages some specific safety equipment used to reduce the spread of fire between compartments such as fire doors. The objective of this work is to propose a theoretical approach that allows the determination of the burning rate of fuels for pool fires in a closed compartment. Fuel response to vitiated air as well as burning enhancement due to hot gases and confinement should be taken into account. Thus, a theoretical formulation, based on an energy balance equation at the pool fire surface, was developed and compared with the empirical correlation of Peatross and Beyler before being implemented in a CFD code " ISIS ", developed at IRSN and validated against PRISME fire test results. The main advantage of this global approach is that no assumptions were made on the relative importance of each mode of heat transfer from the flame. In fact, the convective and the radiant components of the heat flux from the flame to the fuel surface were determined taking into account the air vitiation effect. In addition to this theoretical approach, an experimental work was conducted at the Institut PPRIME to study heptane pool fires in a reduced-scale fire compartment, in the aim to investigate the effects of vitiated air on fire parameters. These results were used to validate the theoretical formulation developed earlier to determine the burning rate of fuels for pool fires in a closed environment. An original method to separate effects of the radiant heat flux of the flame and of the external heat feedback to the fuel surface was developed. These tests also contributed to a better understanding of the effects of ventilation and pan diameter on the fuel pyrolysis at the pool fire surface. As a perspective, the theoretical approach should be extended to address the problem of estimating the flame duration. In this context, the flame extinction process should be treated in more detail by taking into account the detailed kinetics of the chemistry occurring in a flame. Similar experimental works should also be conducted in the aim to study the burning process of a pool fire using different types of fuel (alkenes, ketones, solid fuels...)
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https://tel.archives-ouvertes.fr/tel-00657278
Contributor : Bénédicte Carouge <>
Submitted on : Friday, January 6, 2012 - 11:53:34 AM
Last modification on : Tuesday, June 4, 2019 - 6:21:29 PM
Long-term archiving on: : Monday, November 19, 2012 - 12:40:16 PM

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  • HAL Id : tel-00657278, version 1

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Ayoub Nasr. Détermination par un code CFD de l'évolution de la puissance d'un feu en régime de sous-ventilation dans un milieu confiné et mécaniquement ventilé. Autre. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2011. Français. ⟨tel-00657278⟩

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