Thermal Radiation in Packed and Fluidized Beds

1988 ◽  
Vol 110 (4b) ◽  
pp. 1230-1242 ◽  
Author(s):  
C. L. Tien
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Fluidized Beds ◽  
Radiative Properties ◽  
Phase Boundaries ◽  
Radiation Characteristics ◽  
Theoretical Predictions ◽  
Systems Models ◽  
Reflectance Data

The present work gives an overview of the existing knowledge on radiative transfer in packed and fluidized beds. Special emphasis is given to the proper usage and determination of radiation characteristics of the particles in these systems. Models that treat the particulate bed as a continuum are discussed along with those that consider the system as discontinuous, i.e., accounting for the phase boundaries between the gas and the particles. Existing experimental techniques for determining the radiative properties are presented, and the published bed transmittance and reflectance data are discussed and compared with the theoretical predictions. Interaction of radiation with other modes of heat transfer is also examined.

Impact of Soot Radiative Properties, Pressure and Soot Volume Fraction on Radiative Heat Transfer in Turbulent Sooty Flames

2020 ◽  
Author(s):  
Kevin Torres Monclard ◽  
Olivier Gicquel ◽  
Ronan Vicquelin
Keyword(s):  
Heat Transfer ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Volume Fraction ◽  
Soot Volume Fraction ◽  
Turbulent Flames ◽  
Radiative Properties ◽  
Jet Flame ◽  
Soot Particles

Abstract The effect of soot radiation modeling, pressure, and level of soot volume fraction are investigated in two ethylene-air turbulent flames: a jet flame at atmospheric pressure studied at Sandia, and a confined pressurized flame studied at DLR. Both cases have previously been computed with large-eddy simulations coupled with thermal radiation. The present study aims at determining and analyzing the thermal radiation field for different models from these numerical results. A Monte-Carlo solver based on the Emission Reciprocity Method is used to solve the radiative transfer equation with detailed gas and soot properties in both configurations. The participating gases properties are described by an accurate narrowband ck model. Emission, absorption, and scattering from soot particles are accounted for. Two formulations of the soot refractive index are considered: a constant value and a wavelength formulation dependency. This is combined with different models for soot radiative properties: gray, Rayleigh theory, Rayleigh-Debye-Gans theory for fractal aggregates. The effects of soot radiative scattering is often neglected since their contribution is expected to be small. This contribution is determined quantitatively in different scenarios, showing great sensitivity to the soot particles morphology. For the same soot volume fraction, scattering from larger aggregates is found to modify the radiative heat transfer noticeably. Such a finding outlines the need for detailed information on soot particles. Finally, the role of soot volume fraction and pressure on radiative interactions between both solid and gaseous phases is investigated.

Quartz-Fiber Thermal Insulation: Infrared Radiative Properties and Calculation of Radiative-Conductive Heat Transfer

1996 ◽  
Vol 118 (2) ◽  
pp. 408-414 ◽  
Author(s):  
L. A. Dombrovsky
Keyword(s):  
Heat Transfer ◽  
Disperse Material ◽  
Conductive Heat Transfer ◽  
Radiative Properties ◽  
Conductive Heat ◽  
Radiation Diffusion ◽  
Fiber Thermal Insulation ◽  
Good Agreement ◽  
Scattering And Radiation

Calculations of absorption, transport scattering, and radiation diffusion coefficients for a highly porous material of quartz fibers are performed by use of rigorous scattering theory for arbitrarily oriented cylinders. New results concerning resonance absorption in the semitransparency region and intensive “scattering by absorption” at refractive index n ≈ 1 in the opacity region are obtained. Numerical results for the radiation diffusion coefficient from a theoretical model without taking into account both dependent scattering and interference effects are in a good agreement with the experimental data for isotropic fibrous material of density 144 kg/m3. Calculations allow us to give practical proposals to simplify the determination of optical properties of poly disperse material with randomly oriented fibers. Some results on the radiative–conductive heat transfer in the material considered are presented. The radiation transfer is described in the P1 approximation. A two-band spectral model with bands corresponding to semitransparency and opacity regions is proposed. Applicability of a modified radiative conduction approximation both to transient and to steady-state calculations is discussed.

scholarly journals Radiation Heat Transfer in SOFC Electrolytes

2005 ◽  
Author(s):  
K. J. Daun ◽  
S. B. Beale ◽  
F. Liu ◽  
G. J. Smallwood
Keyword(s):  
Heat Transfer ◽  
Temperature Field ◽  
Thermal Radiation ◽  
Radiation Heat Transfer ◽  
Radiative Properties ◽  
Radiation Heat ◽  
Conduction Model ◽  
D Model ◽  
Sofc Electrolytes

Due to their high operating temperature, there has been speculation that thermal radiation may play an important role in the overall heat transfer within the electrode and electrolyte layers of solid oxide fuel cells (SOFCs). This paper presents a detailed characterization of the thermophysical and radiative properties of the composite materials, which are then used to define a simple 2-D model incorporating the heat transfer characteristics of the electrode and electrolyte layers of a typical planar SOFC. Subsequently, the importance of thermal radiation is assessed by comparing the temperature field obtained using a conduction model with fields obtained using coupled conduction/radiation models. Contrary to some published literature, these results show that radiation heat transfer has a negligible effect on the temperature field within these components, and does not need to be accommodated in comprehensive thermal models of planar SOFCs.

On the Role of Radiation in Low Density Silicon Carbide Foams

2012 ◽  
Author(s):  
Charles C. Tseng ◽  
Ruth L. Sikorski ◽  
R. Viskanta ◽  
Ming Y. Chen
Keyword(s):  
Heat Transfer ◽  
Silicon Carbide ◽  
High Temperature ◽  
Thermal Radiation ◽  
Thermal Protection ◽  
Mie Scattering ◽  
Radiative Properties ◽  
Void Space ◽  
Insulation Systems ◽  
Foam Properties

There are a variety of foams that can be used in thermal protection and/or thermal insulation systems. At high temperature (> 1000 K) thermal radiation may be important or dominate heat transfer in a foam; however, studies based on more detailed thermal radiation analysis are limited. In this paper foams are considered to be semitransparent, because radiation can penetrate through the pore (or void) space and/or foam skeleton (ligament), depending on the materials from which the foams are made. Of particular interest of this study is to understand how the properties of foam material such as its density, mean cell size, etc. affect the radiative transfer through silicon carbide (SiC) foams. In the paper, the dimensionless strut diameter is considered an important parameter of foams, and the radiative properties of the foams are analyzed by Mie scattering theory. The attenuation/extinction behavior of SiC foams can be considered as a function of the dimensionless strut diameter of the foam. The results reveal that the foam properties can significantly reduce radiative heat transfer through the high temperature foam used for the thermal protection.

Modeling and analysis of 3D radiative heat transfer in combustor

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Yue Zhou ◽  
Xijuan Zhu ◽  
Qisheng Guo ◽  
Pengcheng Qi ◽  
Jing Ma
Keyword(s):  
Heat Transfer ◽  
Radiative Transfer ◽  
Thermal Radiation ◽  
Numerical Method ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Radiant Energy ◽  
Radiative Properties ◽  
Direct Technique

Abstract Compared with wall emission, gas thermal radiation is much more complicated because of its nongray and volumetric property. In this paper, a numerical method is established to calculate 3D radiative heat transfer in combustor by modelling radiative transfer as well as nongray radiative properties of combustion gases. Energy exchanges caused by thermal radiation and conduction are calculated and compared in a rectangular combustor, which shows the significant role of thermal radiation in heating fuel-air mixtures and prompting internal combustion reactions. Besides, radiative heat flux on the wall is also quite obvious although a non-contacting flow case, revealing the special challenges for thermal protections brought by radiant energy. Lastly, increasing the working pressure means much more participating species in radiative transfer process and the radiative effects will be also magnified. The numerical method in this paper provides a direct technique to analyze the role of thermal radiation in complex thermochemical reactions while the application case proves the necessity of coupling a high-accuracy radiation model when simulating combustion and flame propagation.

Spectral Thermal Radiation Characteristics of Coal Ashes and Slags: Influence of Chemical Composition and Temperature

2003 ◽  
Author(s):  
S. Linka ◽  
S. Wirtz ◽  
V. Scherer
Keyword(s):  
Heat Transfer ◽  
Chemical Composition ◽  
Thermal Radiation ◽  
Coal Ash ◽  
Spectral Emissivity ◽  
Department Of Energy ◽  
Radiation Characteristics ◽  
Transfer Rates ◽  
Inorganic Species ◽  
Coal Ashes

During the combustion of pulverized coal, ash particles (formed from inorganic species) can deposit on heat-transfer surfaces, resulting in a decrease in heat transfer rates and system efficiency. In addition to the knowledge of the thermal conductivity of the deposits it is necessary to obtain information on the thermal radiation characteristics of the furnace walls to predict the influence of ash sedimentation on heat transfer. At the Department of Energy Plant Technology investigations on the spectral emissivity of different coal ashes and slags were performed applying a spectral radiometer. The samples were electrically heated. Temperatures were varied between 600 and 1400 °C. Emissivities in the range of wavelengths from 1 to 15 μm have been determined. An essential result is that coal ashes show selective thermal radiation characteristics. The main factor of influence on the emissivity is the chemical composition. Therefore, measurements on the single phases SiO2, Al2O3 and MgO were carried out and compared with the emissivity of typical coal ashes and slags. Furthermore, the emissivity depends on temperature, mainly in the wavelength range from 1 to 6 μm.

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