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着重分析了材料的显微结构对材料导热系数的影响:高孔隙率减弱固相传热作用从而使材料的导热系数减小,但是,高孔隙的也增大辐射传热作用。适当降低孔隙可减少辐射传热作用,这在高温时特别明显。尺寸<1mm的孔隙中对流传热被制止,不再对传热起作用。在保持孔隙总量不变的前提下减小孔径可使孔隙数量增大,从而减小导热系数。小于100nm的孔隙可以消除气体本身的热传导,从而极大地减小材料的导热系数。展示了几种不同显微结构的材料及其绝热性能。
The influence of the microstructure of the material on the thermal conductivity of the material is analyzed emphatically: the high porosity reduces the thermal conductivity of the material so as to reduce the thermal conductivity of the material; however, the high porosity also increases the radiative heat transfer. Proper reduction of porosity reduces radiation heat transfer, which is particularly noticeable at high temperatures. Convection heat transfer in pores <1 mm in size is stopped and no longer contributes to heat transfer. Reducing the pore size while keeping the total pore volume unchanged can increase the porosity and reduce the thermal conductivity. Pores smaller than 100 nm can eliminate the heat conduction of the gas itself, thereby greatly reducing the thermal conductivity of the material. Several different microstructured materials and their thermal insulation properties are shown.