Use of a radiation diffusion model for determination of optical and thermal radiative properties of anisotropie silica fiber thermal insulation

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.

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Determination of thermal radiative properties of packed-bed media containing a mixture of polydispersed particles

International Journal of Thermal Sciences ◽

10.1016/j.ijthermalsci.2008.12.006 ◽

2009 ◽

Vol 48 (8) ◽

pp. 1510-1516 ◽

Cited By ~ 7

Author(s):

Klaus Jäger ◽

Wojciech Lipiński ◽

Helmut G. Katzgraber ◽

Aldo Steinfeld

Keyword(s):

Packed Bed ◽

Radiative Properties ◽

Thermal Radiative Properties

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Experimental and Numerical Determination of Thermal Radiative Properties of ZnO Particulate Media

Journal of Heat Transfer ◽

10.1115/1.3194763 ◽

2009 ◽

Vol 132 (1) ◽

Cited By ~ 14

Author(s):

P. Coray ◽

W. Lipiński ◽

A. Steinfeld

Keyword(s):

Radiative Properties ◽

Continuous Beam ◽

Scattering Medium ◽

Measured Intensity ◽

Particulate Media ◽

Varying Thickness ◽

Thermal Radiative Properties ◽

Exponential Trend ◽

Radiative Characteristics

The radiative characteristics of dependently scattering packed-beds of ZnO particles, applied in the design of high-temperature solar thermochemical reactors, were investigated experimentally. ZnO samples of varying thickness were exposed to a continuous beam of near monochromatic thermal radiation in the 0.5–1 μm wavelength range. The overall transmitted fraction measured as a function of sample thickness s obeys an exponential trend exp(−As), with the fit parameter A ranging from 4000±100 m−1 at 555 nm to 2100±100 m−1 at 1 μm. In the forward directions, the measured intensity distribution is approximately isotropic, whereas in the backward directions it is well approximated by a Henyey–Greenstein equation with asymmetry factors g≈−0.4 at 555 nm and g≈−0.1 at 1 μm. A Monte Carlo ray-tracing model of the experimental setup is employed to extract the extinction coefficient and the scattering albedo for the case of a nongray absorbing-scattering medium.

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Experimental and Numerical Determination of Thermal Radiative Properties of ZnO Particulate Media

Heat Transfer: Volume 1 ◽

10.1115/ht2008-56236 ◽

2008 ◽

Cited By ~ 1

Author(s):

Patrick Coray ◽

Wojciech Lipin´ski ◽

Aldo Steinfeld

Keyword(s):

Radiative Properties ◽

Asymmetry Factor ◽

Scattering Medium ◽

Measured Intensity ◽

Particulate Media ◽

Thermal Radiative Properties ◽

Exponential Trend ◽

Set Up ◽

Radiative Characteristics

The radiative characteristics of packed beds of ZnO particles, applied in the design of high-temperature solar thermochemical reactors, were investigated experimentally. ZnO samples of varying thickness were exposed to a continuous beam of near monochromatic thermal radiation in the 0.5–1 μm wavelength range. The overall transmitted fraction measured as a function of sample thickness s obeys an exponential trend exp(–As), with the fit parameter A ranging from (4000 ± 100) m−1 at 555 nm to (2100 ± 100) m−1 at 1 μm. In the forward directions, the measured intensity distribution is approximately isotropic, whereas in the backward directions it is well approximated by a Henyey–Greenstein equation with asymmetry factor g ≈ − 0.4 at 555 nm and g ≈ − 0.1 at 1 μm. A Monte Carlo ray-tracing model of the experimental set-up is employed to extract the extinction coefficient and the scattering albedo for the case of non-grey absorbing-scattering medium.

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