Radiative Heat Transfer in Fibrous Insulations—Part I: Analytical Study

1983 ◽  
Vol 105 (1) ◽  
pp. 70-75 ◽  
Author(s):  
T. W. Tong ◽  
C. L. Tien
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Transport Process ◽  
Analytical Study ◽  
Radiative Heat ◽  
Radiant Heat ◽  
Anisotropic Scattering ◽  
Radiative Properties ◽  
Radiant Heat Flux ◽  
The Mean

The purpose of this work is to develop models for predicting the radiant heat flux in lightweight fibrous insulations (LWFI). The radiative transport process is modeled by the two-flux solution and the linear anisotropic scattering solution of the equation of transfer. The radiative properties of LWFI consistent with these solutions have been determined based on extinction of electromagnetic radiation by the fibers. Their dependence on the physical characteristics of fibrous insulations has been investigated. It has been found that the radiant heat flux can be minimized by making the mean radius of the fibers close to that which yields the maximum extinction coefficient. The results obtained in this study are useful to those concerned with the design and application of LWFI.

A review of radiant heat flux models used in bushfire applications

2003 ◽  
Vol 12 (1) ◽  
pp. 101 ◽  
Author(s):  
A. L. Sullivan ◽  
P. F. Ellis ◽  
I. K. Knight
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Wildland Fire ◽  
Radiant Heat ◽  
Complex Nature ◽  
Radiant Heat Flux ◽  
Common Assumption ◽  
Made In

The need to determine the radiant heat flux (RHF) from bushfires for fire behaviour prediction, firefighter safety, or building protection planning purposes has lead to the development and implementation of a number of RHF models, most of which are based on the Stefan-Boltzmann equation of radiative heat transfer. However, because of the complex nature of bushfire flames, a number of assumptions are made in order to make the implementation of the radiative heat transfer equation practical for wildland fire applications. The main assumptions are: bushfire flame characteristics (geometry, temperature), flame radiative qualities (emission type, emissivity), and the view of the flame at the receiving element. The common assumption of a uniform emissivity of unity and an isothermal rectangular emitting surface produces a generic RHF model described here as an 'opaque box'. Because of the broad assumptions inherent in the opaque box model, it predicts the RHF of bushfires poorly. A comparison is made between the generic opaque box RHF model and the measurements of radiant heat flux emitted by a stationary propane-fuelled artificial bushfire flame front. Knowledge about the geometry and an understanding of the flame characteristics of a bushfire front are needed before generic RHF models will adequately describe the RHF emitted from bushfire flames.

Radiative Heat Transfer in Fibrous Insulations—Part II: Experimental Study

1983 ◽  
Vol 105 (1) ◽  
pp. 76-81 ◽  
Author(s):  
T. W. Tong ◽  
Q. S. Yang ◽  
C. L. Tien
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Radiant Heat ◽  
Radiative Properties ◽  
Analytical Models ◽  
Hot Plate ◽  
Transmission Measurements ◽  
Plate Apparatus

Two experiments have been conducted to study radiative heat transfer in lightweight fibrous insulations (LWFI). The spectral extinction coefficients for a commercial LWFI have been measured via transmission measurements, and a guarded hot plate apparatus has been used to measure the radiant heat flux as well as the total heat flux in the insulation. The experimental results are compared with the theoretical values calculated according to the analytical models presented in Part I of this paper. The comparisons reveal that the analytical models are useful in giving representative values for the radiative properties of typical LWFI. However, only qualitative agreements have been obtained for the heat transfer results.

Spectral Radiative Heat Transfer Analysis of the Planar SOFC

2004 ◽  
Author(s):  
David L. Damm ◽  
Andrei G. Fedorov
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fuel Cells ◽  
Solid Oxide Fuel Cells ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Solid Oxide ◽  
Radiative Properties ◽  
Radiative Heat Flux ◽  
Oxide Fuel

Thermo-mechanical failure of components in planar-type solid oxide fuel cells (SOFCs) depends strongly on the local temperature gradients at the interfaces of different materials. Therefore, it is of paramount importance to accurately predict the temperature fields within the stack, especially near the interfaces. Because of elevated operating temperatures (of the order of 1000 K or even higher), radiation heat transfer could become a dominant mode of heat transfer in the SOFCs. In this study, we extend our recent work on radiative effects in solid oxide fuel cells (Journal of Power Sources, Vol. 124, No. 2, pp. 453–458) by accounting for the spectral dependence of the radiative properties of the electrolyte material. The measurements of spectral radiative properties of the polycrystalline yttria-stabilized zirconia (YSZ) electrolyte we performed indicate that an optically thin approximation can be used for treatment of radiative heat transfer. To this end, the Schuster-Schwartzchild two-flux approximation is used to solve the radiative transfer equation (RTE) for the spectral radiative heat flux, which is then integrated over the entire spectrum using an N-band approximation to obtain the total heat flux due to thermal radiation. The divergence of the total radiative heat flux is then incorporated as a heat sink into a 3-D thermo-fluid model of a SOFC through the user-defined function utility in the commercial FLUENT CFD software. The results of sample calculations are reported and compared against the baseline cases when no radiation effects are included and when the spectrally gray approximation is used for treatment of radiative heat transfer.

Spectral Radiative Heat Transfer Analysis of the Planar SOFC

2005 ◽  
Vol 2 (4) ◽  
pp. 258-262 ◽  
Author(s):  
David L. Damm ◽  
Andrei G. Fedorov
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fuel Cells ◽  
Solid Oxide Fuel Cells ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Solid Oxide ◽  
Radiative Properties ◽  
Radiative Heat Flux ◽  
Oxide Fuel

Thermo-mechanical failure of components in planar-type solid oxide fuel cells (SOFCs) depends strongly on the local temperature gradients at the interfaces of different materials. Therefore, it is of paramount importance to accurately predict the temperature fields within the stack, especially near the interfaces. Because of elevated operating temperatures (of the order of 1000K or even higher), radiation heat transfer could become a dominant mode of heat transfer in the SOFCs. In this study, we extend our recent work on radiative effects in solid oxide fuel cells [J. Power Sources, 124, No. 2, pp. 453–458] by accounting for the spectral dependence of the radiative properties of the electrolyte material. The measurements of spectral radiative properties of the polycrystalline yttria-stabilized zirconia electrolyte we performed indicate that an optically thin approximation can be used for treatment of radiative heat transfer. To this end, the Schuster–Schwartzchild two-flux approximation is used to solve the radiative transfer equation for the spectral radiative heat flux, which is then integrated over the entire spectrum using an N-band approximation to obtain the total heat flux due to thermal radiation. The divergence of the total radiative heat flux is then incorporated as a heat sink into a three-dimensional thermo-fluid model of a SOFC through the user-defined function utility in the commercial FLUENT computational fluid dynamics software. The results of sample calculations are reported and compared against the base line cases when no radiation effects are included and when the spectrally gray approximation is used for treatment of radiative heat transfer.

Optical and radiative properties of clear PMMA samples exposed to a radiant heat flux

2014 ◽  
Vol 82 ◽  
pp. 1-8 ◽  
Author(s):  
P. Boulet ◽  
J. Gérardin ◽  
Z. Acem ◽  
G. Parent ◽  
A. Collin ◽  
...  
Keyword(s):  
Heat Flux ◽  
Radiant Heat ◽  
Radiative Properties ◽  
Radiant Heat Flux

Radiative Heat Transfer Using Isotropic Scaling Approximation: Application to Fibrous Medium

2004 ◽  
Author(s):  
Herve´ T. Kamdem Tagne ◽  
Dominique Doermann Baillis
Keyword(s):  
Heat Transfer ◽  
Radiative Heat ◽  
Radiative Transfer Equation ◽  
Scattering Problem ◽  
Anisotropic Scattering ◽  
Radiative Properties ◽  
Heat Transfer Analysis ◽  
Discrete Ordinate Method ◽  
Discrete Ordinate ◽  
Fibrous Medium

The applicability of the isotropic scaling approximation to heat transfer analysis in fibrous medium is discussed. The isotropic scaling model allows the transformation of an anisotropic scattering problem to an isotropic one. The scaled parameters are derived for general anisotropic scattering and for radiative properties dependent of the incidence direction such as for fibrous medium. The fibers are randomly oriented either in space or parallel to the boundaries of the medium. The radiative transfer equation is solved with the discrete ordinate method and comparisons between the exact and the isotropic scaling problems for several Gauss quadrature are studied.

Numerical analysis of radiative heat transfer in an inhomogeneous and non-isothermal combustion system considering H2O/CO2/CO and soot

2017 ◽  
Vol 27 (9) ◽  
pp. 1967-1985 ◽  
Author(s):  
Zhenhua Wang ◽  
Shikui Dong ◽  
Zhihong He ◽  
Lei Wang ◽  
Weihua Yang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Radiative Properties ◽  
Combustion System ◽  
Radiation Heat ◽  
Radiation Heat Flux ◽  
Participating Media ◽  
Content Type

Purpose H2O, CO2 and CO are three main species in combustion systems which have high volume fractions. In addition, soot has strong absorption in the infrared band. Thus, H2O, CO2, CO and soot may take important roles in radiative heat transfer. To provide calculations with high accuracy, all of the participating media should be considered non-gray media. Thus, the purpose of this paper is to study the effect of non-gray participating gases and soot on radiative heat transfer in an inhomogeneous and non-isothermal system. Design/methodology/approach To solve the radiative heat transfer, the fluid flow as well as the pressure, temperature and species distributions were first computed by FLUENT. The radiative properties of the participating media are calculated by the Statistical Narrow Band correlated K-distribution (SNBCK), which is based on the database of EM2C. The calculation of soot properties is based on the Mie scattering theory and Rayleigh theory. The radiative heat transfer is calculated by the discrete ordinate method (DOM). Findings Using SNBCK to calculate the radiative properties and DOM to calculate the radiative heat transfer, the influence of H2O, CO2, CO and soot on radiation heat flux to the wall in combustion system was studied. The results show that the global contribution of CO to the radiation heat flux on the wall in the kerosene furnace was about 2 per cent, but that it can reach up to 15 per cent in a solid fuel gasifier. The global contribution of soot to the radiation heat flux on the wall was 32 per cent. However, the scattering of soot has a tiny influence on radiation heat flux to the wall. Originality/value This is the first time H2O, CO2, CO and the scattering of soot were all considered simultaneously to study the radiation heat flux in combustion systems.

Radiative Heat Transfer Using Isotropic Scaling Approximation: Application to Fibrous Medium

2005 ◽  
Vol 127 (10) ◽  
pp. 1115-1123 ◽  
Author(s):  
Hervé Thierry Kamdem Tagne ◽  
Dominique Doermann Baillis
Keyword(s):  
Heat Transfer ◽  
Exact Solution ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Scattering Problem ◽  
Incident Radiation ◽  
Anisotropic Scattering ◽  
Radiative Properties ◽  
Heat Transfer Analysis ◽  
Fibrous Medium

The applicability of the isotropic scaling approximation to heat transfer analysis in fibrous medium is discussed. The isotropic scaling model allows the transformation of an anisotropic scattering problem to an isotropic one. The scaled parameters are derived for general anisotropic scattering and for radiative properties dependent of the incidence radiation. Three different isotropic scaling approaches are considered: Directional isotropic scaling, mean isotropic scaling, and P1 isotropic scaling; corresponding to isotropic scaling parameters function of incident radiation, arithmetic mean over all incident direction of radiative properties, and mean on weighted radiative properties, respectively. The discrete ordinate method is used to solve the radiative transfer equation through fibrous medium. The fibers in the medium are randomly oriented either in space or parallel to the boundaries. Numerical results presented for a pure radiation problem show good accuracy on radiative heat flux between the exact solution and solution obtained with both P1 and directional isotropic scaling while using mean isotropic scaling is unsuitable. Using isotropic scaling approximation to model radiative heat transfer is faster than the exact solution and required few quadratures to converge.

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