Radiative heat transfer in ultra-fine powder insulations

Numerical study of radiative properties of nanoporous silica aerogel

“…Since the scale of particles and aggregates is much less than the wavelength of thermal radiation in silica aerogel, the extinction by scattering accounts for a small proportion, and most of extinction is from the absorption of nanoparticles. Chu et al [31] similarly pointed out that the thermal radiation was almost manifested as pure absorption in SiO 2 nanoparticles.…”

“…The fitting equation for the solid thermal conductivity of bulk silicon dioxide k bulk is [38] k bulk ¼ 7:5264 Â 10 À1 þ 3:13 Â 10 À3 T À 4:5242 Â 10 À6 T 2 þ 3:5253 Â 10 À9 T 3 (30) The bulk thermal conductivity should be modified to account for the scale effect on solid heat conduction by Ref. [39] k s ¼ 3r * 4 3r * =4 þ 1 k bulk (31) where r* ¼ r/l is the non-dimensional radius of particles, l is the phonon mean free path of amorphous silicon dioxide, and r is the radius of particles. Fig.…”

Multi-scale Modeling of Radiation Heat Transfer through Nanoporous Superinsulating Materials

“…Here the phenomenon of dependent scattering has to be taken into consideration; this phenomenon leads to a decrease in the scattering efficiency [10] and a simultaneous increase in the absorption efficiency. These tendencies are integrated in our model via very simple correction terms that have been validated (either theoretically or experimentally) over the volume fraction domain f < 0.1 [11]. Eqs.…”

“…If the particles constituting the population are of uniform size (assumption that we make throughout this paper for all the particle populations that we deal with), it is known [6] that the spectral scattering phase function λ (θ ) and hence the associated spectral asymmetry factor g λ are unchanged when referring either to a single particle or to a whole population. Concerning the spectral absorption, scattering, and extinction crosssections (respectively, S abs λ , S sca λ , and S ext λ ) produced by a volume V occupied by the particle population, a very straightforward calculation based on the principle of summation of cross-sections yields (11) so that the spectral absorption, scattering, and extinction coefficients (respectively, κ λ , σ λ , and β λ ) produced by the particle population, defined as the related cumulative cross-sections per unit volume, have the following expressions:…”

The effects of PE additive on the performance of polystyrene vacuum insulation panels

“…Many previous studies have attempted to determine the heat transfer of solid conduction [2][3][4][5], gaseous conduction [5] and thermal radiation [6][7][8][9][10][11][12][13][14][15][16][17][18] in porous medium. Most of the studies assumed all closed-cell or all open-cell structures in their analyses.…”