Analysis of Radiative Heat Transfer in Ultra-Fine Powder Insulations Under Variation of Radiative Boundary Conditions

This paper reports the theoretical investigation of radiative heat transfer through the ultra-fine powder insulation (UFPI) Aerosil 380. The radiative transport process is modeled by the modified diffusion approximation solution and the two-flux solu tion of the equation of transfer. Accuracy of those two approximate methods are in vestigated by comparing the results with those of the Differential-Discrete-Ordinate (DDO) method. The radiative properties of UFPI for dependent effect consistent with these solutions have been determined based on the independent scattering and absorption coefficient which can be calculated by the Rayleigh scattering theory. The influences of the boundary emissivity on radiative heat transfer are also studied. The results show that the radiative thermal conductivity increases very sharply for the black boundary and has a very low value for the low-emissivity boundary. It is sug gested that UFPI systems should always be provided with low-emissivity boundaries around the aerosil powders.