Thermal Radiative Properties of Complex Media: Theoretical Prediction Versus Experimental Identification

Abstract

In many engineering applications and natural phenomena, thermal radiation interacts with complex media composed of dispersed phases that may be of different type: solid/solid, solid/gas, or liquid/gas. Most of them are semitransparent media that emit, absorb, and scatter thermal radiation. Heat transfer by combined radiation with conduction or convection in such media is a problem of high practical importance, mostly in situations where radiation is a dominant mode. Improvement of thermal performance of such materials or of the manufacturing processes that involve these media requires the availability of efficient methods (i) for radiative transfer modeling, and (ii) to predict and to experimentally determine the thermophysical properties intended to feed the models. This paper is focused on radiative properties assessment. After a brief overview of the materials and properties of interest, the emphasis is put on methodology of property investigation combining both theoretical prediction and experimental identification. Examples related to different particulate media are presented, showing recent advances and needs for further investigation.

Spectroscopic diagnostics of morphological changes arising in thermal processing of polypropylene

“…It is clear that the experimental value of S 1.17 cannot be obtained theoretically in the case of optically soft particles (jm q j ≪ 1) [20]. At the same time, we should consider only very small objects, which are not seen in the image of Fig.…”

“…The experimental technique of this type is widely used in studies of semitransparent dispersed materials. Therefore, we do not reproduce here the experimental setup schematics, which can be found elsewhere [18][19][20][21]. The spectral measurements in the wavelength range of 0.67 ≤ λ ≤ 1.1 μm are analyzed in this paper.…”

Near-infrared optical properties of a porous alumina ceramics produced by hydrothermal oxidation of aluminum

“…The spectral measurements of normal-hemispherical reflectance and transmittance of flat samples is a widely-used traditional procedure to get the data for subsequent identification of the main absorption and scattering characteristics of dispersed materials [9][10][11]. In some cases, as discussed in [12][13][14], porous materials are highly scattering in the near-infrared.…”

“…Eqs. (9a), (9b) and (11) can be employed to retrieve transport scattering albedo from the measured normal-hemispherical reflectance.…”

Determination of radiative properties of polyester batting insulation material from hemispherical transmittance and reflectance measurements

“…axial symmetry, no emission, medium considered as being isotropic and the limits of the phase function usually used HenyeyGreenstein phase function associated with the function of Lorentz). Thus, J. F. Sacadura [9] presented a method combining both theoretical prediction and experimental identification of the radiative properties of semitransparent materials. Moreover, a few works have been reported for the heat transfer through the polyester insulating; McKay et al [10] have been used the Mie theory to determine the extinction coefficient and absorption of the polyester fiber with randomly oriented fibers.…”