论文部分内容阅读
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.
The mesoporous silica substrate contains discontinuous and uniformly distributed spherical pores. Since the pore size is smaller than the characteristic wavelength of the thermal radiation, the near-field radiation can not be ignored. Based on the fluctuation dissipation theory and the dyadic Green’s function, The near-field radiation heat transfer in the spherical silica sphere hole and the equivalent thermal conductivity of the near-field radiation obtained therefrom will be further used to correct the effective thermal conductivity of the mesoporous silica. The rare-earth porosity- The near field radiation equivalent thermal conductivity, the limited gas thermal conductivity in the pores and the thermal conductivity of the mesoporous silica substrate, the effective thermal conductivity of the mesoporous silica was obtained, and the influence of the pore diameter and the temperature was further investigated. Under the mesoscopic scale, the radiative heat flux is 2 ~ 7 orders of magnitude higher than that at the macroscopic scale.The heat flux and equivalent thermal conductivity of the near-field radiation in the spherical pores decrease exponentially with the increase of the pore size and increase with the increase of the temperature The effective thermal conductivity of mesoporous silica decreases with the increase of porosity and slowly increases with the increase of temperature.The smaller the pore size, the more significant the effect of near-field radiation can not be ignored.When the hole Greater than 50 nm, the size of the effect gradually disappeared.