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A numerical study of the interaction between thermal radiation and laminar mixed convection for ascending flows of emitting and absorbing gases in vertical tubes is presented. The radiative properties of the flowing gases, H2O, CO2 and H2O–CO2 mixtures are modeled by using the global absorption distribution function model. The temperature-dependent thermophysical properties are considered when solving the flow field and energy balance equations. Results are presented in terms of velocity and temperature fields, and of evolution of centerline velocity, friction factor and heat fluxes. The effects of radiation on the regime of reverse flow occurrence are also examined. It is shown that, for heated gases, radiation tends to reduce the velocity distortion effect of buoyancy. Radiative transfer delays then significantly the occurrence of reverse flow for heated gases while, for cooled gases, the flow regime is practically not affected. [Copyright &y& Elsevier]

The two-dimensional combined radiative and convective transfer in emitting and absorbing real gases in the entrance region of a duct with a jump of wall temperature is studied. The axial propagation of radiation is taken into account in the analysis. The flow field and the energy equations are solved simultaneously and the radiative properties of the flowing gases, CO2 or H2O, are modeled by using either the narrow-band correlated-k model or the global absorption distribution function (ADF) model. The results are presented in terms of temperature and radiative power fields, and of the evolution of bulk temperatures and of heat transfer coefficients. Due to the axial component of the radiative flux, the gas is preheated or precooled before the change in wall temperature and this induces a persistent difference between the results of 1-D and 2-D radiation analyses. Some differences between CO2 and H2O temperature and radiative power profiles, due to the different structures of their spectra, are put in evidence. The ADF model, only suitable for gray walls, is shown to be less accurate when the gas is heated than when it is cooled. [Copyright &y& Elsevier]

The aim of this paper is to provide upper bounds of the radiation emitted by hot combustion products, mainly CO 2 and H 2 O, and absorbed by some gaseous cold hydrocarbons, or by cold CO 2 and H 2 O. Line by line calculations with accurate spectroscopic data bases are used to compute the absorbed power under two geometrical configurations: a cold optically thin medium surrounded by spherical hot combustion products, and a thin cold slab in front of a hot combustion parallel slab. The absorbed power and the corresponding characteristic time scale are adjusted by simple and physically based formulas to provide quick estimations for various values of combustion product temperature, pressure, and the radius of the hot sphere or the hot slab thickness. The obtained time scales can be compared in a given application to hydrodynamic or diffusive time scales to decide whether it is necessary to take this preheating phenomenon into account or not. [ABSTRACT FROM AUTHOR]

This paper presents the development of a Statistical Narrow Band (SNB) model for CO 2 in a nonequilibrium vibrational state. The population densities of the energy levels are modeled by a three-temperature approach (T , T 12 , T 3) associated resp. to translation–rotation modes, symmetric-stretching and bending modes, and antisymmetric stretching mode, to compute nonequilibrium line by line (LBL) spectra. The nonequilibrium between vibrational temperatures induces spectral correlation issues between η σ / κ σ and κ σ , where η σ and κ σ are the emission and absorption coefficients respectively. To overcome this issue, a vibrational splitting of the spectroscopic database is made to separate lines with completely different vibrational transitions. The SNB parameters are obtained by fitting the curves of growth from the LBL approach by a least squares error minimization using a Newton method for pure Lorentz and Doppler broadening regimes for each line class. The total SNB transmissivity is obtained by computing the product of each line class transmissivity, and the decorrelation between the spectra of the different classes is checked. Finally, the model is tested in Voigt broadening regime using a mixing rule by computing outlet radiative intensity of uniform and non-uniform columns and agrees well with the LBL approach. SNB parameters are available under request to the corresponding author. • A 3-temperature SNB model is developed for vibrational nonequilibrium CO 2 radiation. • CO 2 lines are grouped into classes with similar vibrational transitions. • Emission to absorption ratio and absorption spectra of each class are uncorrelated. • The model is implemented over a wide pressure range under Voigt broadening regime. • The model is applied to high altitude expanding plumes. [ABSTRACT FROM AUTHOR]

Abstract: It is well known that the Kirchhoff''s law, connecting emission to absorption through the Planck''s function, is no more valid when the medium is not at local thermal and chemical equilibrium. The aim of the present paper is to analyze the effects of this nonequilibrium on radiative transfer, and in particular, for atmospheric air re-entry applications. A general formulation is proposed in the framework of multi-temperature description of the thermodynamic state of the gas mixture. Application of this model to simulate an earth re-entry experiment first leads to a reasonable agreement and then outlines important effects of chemical nonequilibrium, especially through bound–free transitions. [Copyright &y& Elsevier]

• A consistent model for CO 2 radiation under nonequilibrium conditions is developed. • Vibrational radiation source terms are derived from partial absorption and emission coefficients. • Vibrational temperature fields are obtained from Lagrangian post-processing of equilibrium calculations. • The model is applied to a nozzle expanding flow and to a high altitude rocket plume. • Emitted radiation is significantly increased due to the partial freeze of vibrational excitation. The aim of this paper is to develop a line by line model for CO 2 vibrational nonequilibrium radiation and to investigate nonequilibrium effects in the case of some applications involving high temperature expanding flows. A vibrational specific collisional relaxation model is developed and is incorporated in a multi-temperature thermodynamic description of the gas mixture, in order to compute vibrational level populations along the flow. The HITEMP-2010 spectroscopic database is employed with a model for level energy splitting to provide line by line absorption and emission total and per-vibrational mode specific spectra. The specific spectra allow us to derive the radiative source terms to be used in the multi-temperature model if a coupled approach is required. The model is applied first to a simple conical nozzle flow and then to the plume of a high altitude solid propellant rocket engine. It is shown that, for the considered applications, the partial freeze of vibrational excitation in the expanding flow increases significantly the radiative intensity escaping from the mixture. [ABSTRACT FROM AUTHOR]