工程科学学报
工程科學學報
공정과학학보
Journal of University of Science and Technology Beijing
2015年
8期
1063-1068
,共6页
李静%冯妍卉%张欣欣%黄丛亮%杨穆
李靜%馮妍卉%張訢訢%黃叢亮%楊穆
리정%풍연훼%장흔흔%황총량%양목
介孔材料%二氧化硅%近场%辐射%导热系数
介孔材料%二氧化硅%近場%輻射%導熱繫數
개공재료%이양화규%근장%복사%도열계수
mesoporous materials%silica%near field%radiation%thermal conductivity
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。
介孔二氧化硅基材內含不連續且均勻分佈的毬形孔。由于孔徑小于熱輻射特徵波長,近場輻射作用不容忽視。本文基于漲落耗散理論和併矢格林函數,計算介孔二氧化硅毬形孔內的近場輻射換熱,由此得到的近場輻射的噹量導熱繫數,將進一步用來脩正介孔二氧化硅的有效導熱繫數。採用稀介質孔隙率加權模型耦閤毬形孔內近場輻射噹量導熱繫數、孔內受限氣體導熱繫數及介孔二氧化硅基材導熱繫數,得到介孔二氧化硅的有效導熱繫數,併進一步攷察瞭孔徑和溫度的影響。研究結果錶明,在介觀呎度下,其輻射熱流比宏觀呎度下要高2~7箇數量級。毬形孔內近場輻射的熱流及噹量導熱繫數隨著孔徑的增加呈指數衰減,隨著溫度的升高而增大。介孔二氧化硅的有效導熱繫數隨著孔隙率的增加逐漸減小,隨著溫度的升高緩慢增加。孔徑越小,近場輻射的作用越顯著,不容忽視。噹孔徑大于50 nm時,呎吋效應逐漸消失。
개공이양화규기재내함불련속차균균분포적구형공。유우공경소우열복사특정파장,근장복사작용불용홀시。본문기우창락모산이론화병시격림함수,계산개공이양화규구형공내적근장복사환열,유차득도적근장복사적당량도열계수,장진일보용래수정개공이양화규적유효도열계수。채용희개질공극솔가권모형우합구형공내근장복사당량도열계수、공내수한기체도열계수급개공이양화규기재도열계수,득도개공이양화규적유효도열계수,병진일보고찰료공경화온도적영향。연구결과표명,재개관척도하,기복사열류비굉관척도하요고2~7개수량급。구형공내근장복사적열류급당량도열계수수착공경적증가정지수쇠감,수착온도적승고이증대。개공이양화규적유효도열계수수착공극솔적증가축점감소,수착온도적승고완만증가。공경월소,근장복사적작용월현저,불용홀시。당공경대우50 nm시,척촌효응축점소실。
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.