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Show an one dimensional flame to analyze the interactions among heat radiatio~ conduction and convection. S. W. Baek and C. Lee [3] observed the thermal feedback of conduction, convection and radiation in a thermally radiating medium. The flame and fuel surfaces were assumed to be diffusive, non-black and isothermal parallel surfaces separated by a finite intervals. The space 1IlI.l&,,"' ...... these surfaces was assumed to be full of absorbing, emitting, and scattering radiation mediums. A differential equation was used to completely descn1>e such a problem. W. H. Dalzell and A F. Sarofim [4] had obtained the optical constants of soot with a wavelength range betw~n 0.4 to O. 8 ~, and 2.5 to 1 0 ~ under room temperature. Dispersion formulas are developed for interpolating the data between 0.8 and 2.5 ~ . These results can be used to derive the spectral absorption coefficient, and the total emissivities of soot suspensions. T. T. Cbaralampopoulos and H. Chang [5] inferred spectral optical properties of soot particles in the visible and infrared part of the spectrum. Particle size distribution, number densities, and the volume fraction of soot are detennined and comparisons are with the existing soot optical constants, the effects of agglomeration and temperature in the determination of the optical properties. Z. G. Habib and P. Vervisch [6] conducted a study on the optical constant data of soot in the visible and infrared (0 .4-5 J.U7I) under flame temperature. Both real and imaginary parts of the refractive index are determined from in-situ extinction coefficient spectra by fitting to theoretical spectra calculated by using the Mie theory in conjunction With a dispersion model. B. 1. Stagg and T. T. Charalampopoulos [7] explored the relationship between changes in the temperature and the refractive indices of carbonaceous materials (pyrolytic graphite, amorphous carbo~ and flame soot) from ellipsometric intensity measurements under the temperature of 25 to 600 0 C, and the wavelength of O. 4-{). 7 J.U7I . Finally, it was found that the inferred refractive index shows insignificant variation with temperature for this range of temperature and wavelength. This paper. studies the heat transfer of turbulent premixed flamelet in two directions. One is the establishment of the heat transfer model of the preheat zone in the flame front, which seeks to investigate the changes among heat conduction, convection and radiation. The other is the discussion of the individual contributions toward the absorption coefficient and emissivity of medium radiation by various gases (wide band model), combustion soot (the Drude-Lorentz dispersion model). n. NUMERICAL SIMULATION 2.1 Heat Transfer Model [3][8][9][10][11] A heat transfer model was established, which regarded flame as a flamelet (Figure 1). In this model, only the changes facing the flame surface were considered. The changes on the tangential side of the flame surface were regarded as infinite extensions, and neglected. The following assumptions on the physical, chemical and optical properties and flow field distribution of the medium particles in the preheat zone of the flame front were made as fallows: 1. Steady state or quasi-steady state transport. 2. Gas flow and heat transfer are one dimensional. 3. Constant specific heat in the mediums. 4. Gas and solid particulate flows in homogeneous, thermodynamic equilibrium. S. The heat -conduction coefficient of the radiating medium is constant. 6. Isotropic scattering, constant absorption and scattering coefficient. (i) Governing Equations: 2 |
