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Research Papers

Radiative Characteristics of High-Porosity Media Containing Randomly Oriented Fibers in Space

[+] Author and Article Information
Herve Thierry Tagne Kamdem

Laboratory of Mechanics and Modeling
of Physical Systems,
Department of Physics,
Faculty of Science,
University of Dschang,
P. O. Box 67,
Dschang, Cameroon
e-mail: herve.kamdem@univ-dschang.org; ttagne@gmail.com

Contributed by the Heat Transfer Division of ASME for publication in the JOURNAL OF THERMAL SCIENCE AND ENGINEERING APPLICATIONS. Manuscript received April 22, 2016; final manuscript received January 21, 2017; published online March 7, 2017. Assoc. Editor: Dr. Sandra Boetcher.

J. Thermal Sci. Eng. Appl 9(2), 021014 (Mar 07, 2017) (9 pages) Paper No: TSEA-16-1107; doi: 10.1115/1.4035839 History: Received April 22, 2016; Revised January 21, 2017

This paper proposed radiative characteristics' expressions for media containing randomly oriented fibers in space. In deriving these simple radiative characteristics' expressions, the fibrous medium effective extinction coefficient is defined to match with the one of large particle obtained by combining geometric optics and Fraunhofer diffraction theory. Fibrous media radiative characteristics are then derived as an average over all incident radiation angles of single fiber radiative characteristics. Theoretical hemispherical reflectance and normal transmittance predictions using the proposed fibrous media radiative characteristics based on the Mie theory agreed well with literature experiments. Therefore, media containing fiber randomly oriented in space can be scaled to a suitable equivalent media such that scattering mechanisms behave similarly to that occurring in a participating media containing spherical particles. Numerical investigations show that a theoretical model which assumes Henyey–Greenstein (HG) scattering phase function can conveniently be used for the estimation of equivalent fibrous media radiative characteristics using hemispherical reflectance measurements. On the other hand, the estimated equivalent fibrous media radiative characteristics from hemispherical measurements and using a two-flux model with isotropic scaling radiative characteristics may be subjected to serious errors in the case of semitransparent media for which the absorption is significant.

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References

Figures

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Fig. 1

Geometry of scattering by a tilted fiber

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Fig. 2

Variation of the corrected extinction versus the size parameter for a purely scattering (λ=1.5 μm) and absorbing/scattering media (λ=5.0 μm)

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Fig. 3

Radiative heat transfer problem through a fibrous insulation medium

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Fig. 4

Complex refractive index of fused quartz

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Fig. 5

Comparison between present and Tong and Tien [13] effective extinction efficiency

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Fig. 6

Effective extinction efficiency of high-porosity fibrous medium at wavelength λ=1.5μm and 5.0μm

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Fig. 7

Scattering phase function of a purely scattering medium (λ=1.5 μm) and an absorbing scattering medium (λ=5.0 μm)

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Fig. 8

High-porosity fibrous medium scattering albedo and asymmetry factor

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Fig. 9

Spectral hemispherical reflectance of bonded silica fiber insulation medium consisting of randomly oriented fibers in space with fvL=0.0102 cm

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Fig. 10

Spectral hemispherical reflectance of bonded silica fiber insulation medium consisting of randomly oriented fibers in space with fvL=0.0150 cm

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Fig. 11

Spectral normal transmittance of bonded silica fiber insulation media consisting of fibers randomly oriented in space with fvL={0.0072,0.0114} cm 

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