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 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.

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.

Effect of Radiative Heat Transfer Factor on the Temperature Distribution of a First Stage Vane

2014 ◽  
Author(s):  
Hong Yin ◽  
Mingfei Li ◽  
Zhongran Chi ◽  
Jing Ren ◽  
Hongde Jiang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Temperature Distribution ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Swirling Flow ◽  
Inlet Temperature ◽  
Radiative Effect ◽  
Turbine Inlet Temperature ◽  
Turbine Inlet

As the advanced heavy-duty gas turbine develops, the turbine inlet temperature and pressure have increased quite significantly to achieve better performance. The flow and heat transfer conditions of hot components including combustor and turbine become even more extreme than ever which need corresponding aerodynamic and cooling design development. The issue of combustor-turbine interaction has been proposed as a complicated research topic. Currently the hot streak, turbulence intensity, swirling flow, radiation are the four important factors for combustor-turbine interaction research according to the literature. Especially as the turbine inlet temperature increases, the radiative heat transfer plays a more and more important role. In this paper, a first stage vane is selected for the conjugate heat transfer simulation including radiative heat transfer since it is almost impossible to identify the radiative effect in experiment. The goal is to examine the effects of radiative heat flux and temperature increment caused by radiation. Several radiative factors including the inlet radiation, gas composition, vane surface emissivity and outlet reflection are investigated. The temperature distribution and heat flux enhancement under different conditions are compared, which can provide reference to the turbine heat transfer design. The general information of radiative effect can be summarized by quantitative analysis. Results show that the temperature increases obviously when considering the radiation effect as expected. However, these factors show distinct influence on the vane temperature distribution. The inlet radiation has significant impact on the vane leading edge and pressure side. Besides the gas radiation plays quite uniform on the whole vane surface.

Near-Field Radiative Heat Transfer Between Mie Resonance-Based Metamaterials Made of Coated Nonmagnetic Particles

2019 ◽  
Author(s):  
Lu Lu ◽  
Jinlin Song ◽  
Kun Zhou ◽  
Qiang Cheng
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Liquid Crystals ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Nematic Liquid Crystals ◽  
Near Field ◽  
Core Shell ◽  
Mie Resonance ◽  
Shell Particles

Abstract Near-field radiative heat transfer between Mie resonance-based metamaterials composed of SiC/d-Si (silicon carbide and doped silicon) core/shell particles immersed in aligned nematic liquid crystals are numerically investigated. The metamaterials composed of core/shell particles exhibit superior performances of enhanced heat transfer and obvious modulation effect when compared to that without shell. The underlying mechanism can be explained that the excitation of Fröhlich mode and epsilon-near-zero (ENZ) resonances both contribute to the total heat flux. Modulation of near-field radiative heat transfer can be realized with the host material of aligned nematic liquid crystals. The largest modulation ratio could be achieved as high as 0.45 for metamaterials composed of core/shell SiC/d-Si particles, and the corresponding heat flux is higher than other similar materials such as LiTaO3/GaSb and Ge/LiTaO3. While with the same volume filling fraction, the modulation ratio of that composed of SiC particles is only 0.2. We show that the core/shell nanoparticles dispersed liquid crystals (NDLCs) have a great potential in enhancing the near-field radiative heat transfer in both the p and s polarizations with the radii of 0.65 μm, and Mie-metamaterials are shown for the first time to modulate heat flux within sub-milliseconds.

Modeling Thermal Radiation With Focus on Particle Radiation in Grate Fired Furnaces Combusting MSW or Biomass: A Parametric Study

2013 ◽  
Author(s):  
Henrik Hofgren ◽  
Bengt Sundén
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Fly Ash ◽  
Thermal Radiation ◽  
Radiative Heat Transfer ◽  
Parametric Study ◽  
Radiative Heat ◽  
Size Distributions ◽  
Particle Radiation ◽  
Mass Size

This parametric study shows that thermal radiation from particles, fly ash and char, can be highly relevant for estimating the radiative heat flux to surfaces in grate fired furnaces, especially to the hot bed. The large effects of particle radiative heat transfer come from cases with municipal solid waste (MSW) as fuel whereas biomass cases have moderate effect on the overall radiative heat transfer. The parameters investigated in the study were the fuel parameters, representing a variety of particle loads and size distributions, emissivities of walls and bed, and the size of furnace. The investigations were conducted in a 3-D rectangular environment with a fixed temperature field, and homogeneous distribution of gases and particles. The choice of boundary emissivity was found to be much more or equally important as the particle radiation effects, dependent if biomass or MSW, respectively, was used as the fuel. The effect of particle radiation increased with increasing furnace size, mostly evident in the change of the radiative source term and the heat flux to the bed. Compared to previous studies of particle radiation in grate fired combustion, this study used realistic particle mass size distributions for fly ash. Estimates of char mass size distributions inside the furnace were conducted and used.

A Numerical Study of Radiative Heat Transfer in a Cylindrical Furnace by Using Finite Volume Method

2016 ◽  
Author(s):  
Zhenhua Wang ◽  
Bengt Sunden ◽  
Shikui Dong ◽  
Zhihong He ◽  
Weihua Yang ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Finite Volume Method ◽  
Finite Volume ◽  
Radiative Heat Transfer ◽  
Radiative Heat ◽  
Numerical Study ◽  
Radiative Heat Flux ◽  
Computational Time ◽  
Volume Method

In designing industrial cylindrical furnaces, it is important to predict the radiative heat flux on the wall with high accuracy. In this study, we consider CO2 and H2O which have strong absorption in the infrared range. The absorption coefficients of the gases are calculated by using the statistical narrow band (SNB) model. The spectrum is divided into 15 bands to cover all the absorption regions of the two non-gray gases. The radiative transfer equation is solved by the finite volume method (FVM) in cylindrical coordinates. To make the FVM more accurate, we discretize the solid angle into 80 directions with the S8 approximation which is found to be both efficient and less time consuming. Based on the existing species and temperature fields, which were modeled by the FLUENT commercial code, the radiative heat transfer in a cylinder combustor is simulated by an in-house code. The results show that the radiative heat flux plays a dominant part of the heat flux to the wall. Meanwhile, when the gas is considered as nongray, the computational time is very huge. Therefore, a parallel algorithm is also applied to speed up the computing process.

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