Evaluation of Radiative Heat Transfer in High-Temperature Porous Insulation Materials by Using Diffusion Approximation

Abstract

導率と温度の関係から，ふく射物性として Rosseland 平均減衰係数を求めた．更に，有効熱伝導率に 対して，固体による熱伝導，気体による熱伝導，ふく射伝熱が与える影響について分離して評価を行 った．各伝熱機構が持つ影響の温度依存性を考察し，多孔質断熱材の断熱性能向上におけるふく射伝 熱の重要性を定量的に示すことができた． This paper describes the radiative heat transfer in porous insulation materials at high temperature. The heat transfers in porous insulation materials are heat conduction through solid and gas, convection of gas and thermal radiation.In this study, a diffuse approximation was applied to several types of porous insulation materials and the radiative heat transfer was considered in proportion to the cube of temperature, T 3. From the literature data of the effective thermal conductivity, the Rosseland mean extinction coefficient was estimated and the contributions of heat transfer by solid, gas, and radiation were estimated separately.The estimation results indicate that the effective thermal conductivities depend on the radiative heat transfer over a wide range of temperature. Additionally for the improvement of insulation performance, the reduction of radiative heat transfer is necessary not only in high temperature condition but also for low and normal temperature conditions. [Keywords: insulation material, effective thermal conductivity, radiative thermal conductivity]