学术论文

      介孔二氧化硅球形孔内近场辐射换热

      Near-field radiation across a spherical pore in mesoporous silica

      摘要:
      介孔二氧化硅基材内含不连续且均匀分布的球形孔。由于孔径小于热辐射特征波长,近场辐射作用不容忽视。本文基于涨落耗散理论和并矢格林函数,计算介孔二氧化硅球形孔内的近场辐射换热,由此得到的近场辐射的当量导热系数,将进一步用来修正介孔二氧化硅的有效导热系数。采用稀介质孔隙率加权模型耦合球形孔内近场辐射当量导热系数、孔内受限气体导热系数及介孔二氧化硅基材导热系数,得到介孔二氧化硅的有效导热系数,并进一步考察了孔径和温度的影响。研究结果表明,在介观尺度下,其辐射热流比宏观尺度下要高2~7个数量级。球形孔内近场辐射的热流及当量导热系数随着孔径的增加呈指数衰减,随着温度的升高而增大。介孔二氧化硅的有效导热系数随着孔隙率的增加逐渐减小,随着温度的升高缓慢增加。孔径越小,近场辐射的作用越显著,不容忽视。当孔径大于50 nm时,尺寸效应逐渐消失。
      Abstract:
      A mesoporous silica substrate consists of uniformly distributed and unconnected spherical pores. Since the pore diame-ter is less than the characteristic wavelength of thermal radiation, near-field radiative heat transfer cannot be ignored. In this paper, near-field radiation across a spherical pore in mesoporous silica was simulated by employing the fluctuation dissipation theorem and the Green function. The calculated equivalent thermal conductivity of radiation was further developed to modify the thermal conductivity of mesoporous silica. The combined thermal conductivity of mesoporous silica was obtained by using the porosity weighted dilute medium ( PWDM) model to combine the equivalent thermal conductivity of radiation across the pore, the thermal conductivity of confined air in the pore and the thermal conductivity of the silica substrate. Such factors as the pore diameter and the material temperature were fur-ther analyzed. Research results show that the radiative heat transfer at the mesoscale is 2-7 orders higher than that at the macroscale. The heat flux and equivalent thermal conductivity of radiation across a spherical pore decrease exponentially with increasing pore diam-eter, but increase with increasing temperature. The combined thermal conductivity of mesoporous silica decreases gradually with in-creasing pore diameter, while increases smoothly with increasing temperature. The smaller the pore diameter, the more significant the near-field effect, which cannot be ignored. When the pore diameter is greater than 50 nm, the size effect gradually disappeared.
      作者: 李静 [1] 冯妍卉 [2] 张欣欣 [2] 黄丛亮 [2] 杨穆 [3]
      Author: LI Jing [1] FENG Yan-hui [2] ZHANG Xin-xin [2] HUANG Cong-liang [2] YANG Mu [3]
      作者单位: 重庆大学动力工程学院,重庆400044; 北京科技大学机械工程学院,北京100083 北京科技大学机械工程学院,北京,100083 北京科技大学材料科学与工程学院,北京,100083
      刊 名: 工程科学学报 ISTICEIPKU
      年,卷(期): 2015, (8)
      分类号: TK124
      机标分类号: TB3 O4
      在线出版日期: 2015年9月22日
      基金项目: 国家自然科学基金资助项目,国家重点基础研究发展计划资助项目,国家科技支撑计划资助项目