尺寸效應對多孔性奈米線之熱傳導分析

Abstract

本文旨在探討二維多孔性奈米線之熱傳現象，當材料尺寸縮小至微奈米級時，傳統的傅立葉定律已不再適用，因此本文利用聲子幅射熱傳方程式分析配合非均勻網格來描述多孔性奈米線的熱傳現象。本文主要探討奈米線線寬、孔隙大小、孔隙表面積及孔隙間距對多孔性奈米線的影響。 本文發現當多孔性奈米線線寬小於或等於聲子平均自由徑時，此時奈米線受到尺寸效應的影響，奈米線的熱傳導係數不再是定值，而會隨著材料線寬大小而有變化。此時孔隙大小、孔隙表面積及孔隙間距都會對奈米線的熱傳導係數產生明顯的影響；孔隙直徑、表面積越大時，熱傳導係數會越低。另外當發生尺寸效應時，孔隙間距對熱傳導係數也會有明顯的影響，隨著孔隙不同的排列方式及位置，都會影響多孔性奈米線的熱傳導係數。

The microscale heat transfer phenomena of two-dimensional porous nanowires were investigated based on the microscopic heat transport theory. The phonon Boltzmann equation model was established to analyze the size effect on the thermal conductivity of porous nanowires. The effects of pore size, pore surface area and the distance between pores were emphasized in present study. Numerical analysis was conducted to estimate the thermal conductivity of porous silicon nanowires. The results showed that, unlike the bulk material, thermal conductivity of the wire did not remain constant when the phonon mean free paths were comparable with or even larger than the diameter of wire. The pore size, pore surface area and the distance between pores showed pronounced effects on the thermal conductivity of the wire. The pore size affects the probability of the collision of phonons with the pore boundary, which indicates that the thermal conductivity of the wire increases with decreasing pore size. The results could be used to direct the development of high-efficiency thermoelectric materials.