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Couplage de la convection naturelle et du rayonnement dans les mélanges gazeux absorbants-émettants

Abstract : This work deals with the impact of the gas radiation on the natural convection flow in a square cavity containing a binary gaseous mixture where at least one component radiates in the infrared. In the first chapter, we present the numerical methods thus developed and used in the calculation. They rely on a model of radiation based on the discrete ordinate method (for solving the equation of radiative transfer in given spectral conditions) and model SLW to take into account the real gas absorption spectrum. This radiative module has been implemented in the CFD AQUILON code developed in the laboratory TREFLE (Bordeaux-France). In the second chapter, we investigate the effect of the gas radiation on the laminar transient double diffusive convection flow in a cavity containing mixtures of air-CO2 or H2O. The air is treated here as a fully transparent gas for infrared radiation and the pollutant (CO2 or H2O) is the absorbing species. The resulting flow is generated by Archimedean forces when the fluid is subjected simultaneously to temperature and concentration changes. In this configuration, there is a direct coupling between heat and mass fields through the radiative properties of mixture. Indeed, the variations in concentration of the absorbing species (CO2 or H2O) modify locally the emissionabsorption properties of the fluid and therefore influence sources and fluxes of radiative origin. This new type of coupling induces a radical change in the dynamic flow and the associated transfers affecting the stability's flow conditions. It shows in particular that, in opposite configuration, gas radiation promotes the maintenance of thermosolutale instability which is preventing the establishment of a stationary solution. In the third chapter, we are interested in the effect of the radiative contribution of water vapour on the turbulent convection in a cavity filled with humid-air (a representative case of a building piece, for example).The equations of momentum and energy conservation have been treated in turbulent regime by LES approach for a Rayleigh number of the order of 1.5 × 109. It shows that even if the mole fraction of acquiring gas is low (xH20 = 0.0115), the gas radiation affects heat and dynamic of the flow when the cavity's dimensions become large. In particular, the thermal stratification in the center of the cavity is mitigated.
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https://tel.archives-ouvertes.fr/tel-00463886
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Submitted on : Monday, March 15, 2010 - 2:09:40 PM
Last modification on : Tuesday, June 4, 2019 - 6:21:15 PM
Long-term archiving on: : Friday, June 18, 2010 - 9:21:52 PM

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  • HAL Id : tel-00463886, version 1

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Adel Ibrahim. Couplage de la convection naturelle et du rayonnement dans les mélanges gazeux absorbants-émettants. Sciences de l'ingénieur [physics]. ISAE-ENSMA Ecole Nationale Supérieure de Mécanique et d'Aérotechique - Poitiers, 2010. Français. ⟨tel-00463886⟩

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