红外遮光剂选材的理论研究

Theory Research on Selection of Infrared Opacifiers

SiO_2气凝胶纳米孔材料导热系数极低,代替传统绝热材料可以降低绝热层厚度,节约能源。高温时SiO_2气凝胶绝热性能下降,可以添加矿物粒子遮蔽辐射传热,提高其高温时的绝热性能。文中采用Mie散射理论建立起了遮光气凝胶热辐射特性和辐射热导率的定量理论模型,分析了遮光剂光学参数,粒子尺度对辐射传热的影响,对比了SiC、B_4C、BN、TiO_2遮光剂的遮光效果。结果表明,遮光剂的折射率对辐射传热的影响较大,折射率越大,对辐射传热的衰减效果越好。在研究的材料中,遮光效果最好的是B_4C,其次依次是BN、Si C和TiO_2。特定温度下,存在最优粒径使得遮光气凝胶的辐射热导率最小,最优粒径随着温度升高而变小,对于文中计算的遮光剂,300 K时最优粒径约为1.4μm,700 K时约为0.8μm。分析结果对于指导遮光剂的选材,提高材料的性能,降低制备成本具有工程应用价值。

Silica aerogel, with extreme low thermal conductivity, can be used to replace traditional thermal insulation materials, resulting in less thickness of insulation layer and saving energy. At high temperature,the insulation property of silica aerogel drops. The mineral particles can be added in it to attenuate the radiant heat transfer in order to raise the insulation property of silica aeroge. The quantitative theory model of the radiation characteristics and radiation thermal conductivity of the opacified aemgel were established based on the Mie scattering theory in this paper. The influence of the optical parameter and the particle size of the opacifier on the radiation heat transfer was analyzed and the opacifying performance of the SiC, B4C, BN, TiO/ particle was compared. It was shown that, the radiation heat transfer is seriously affected by the refractive index of the opacifier, the higher the refractive index is, the better the opacifying performance shows. The opacifying effect of BaC is the best among these,followed by BN, SiC, and TiO2. At a particular temperature, there is an optimized particle size resulting in the least thermal conductivity of the aerogel opacifier, and the optimized particle size decreases with the increase of the temperature. For opacifiers in this paper,the optimized particle size is 1.4 μm at 300 K,while 0.8 μm at 700 K. The conclusions can be used to select a better opacifier, improve the thermal insulation performance of the materials and saving the manufacturing cost.