二氧化鈦奈米流體熱傳導性質的實驗探討

Abstract

奈米流體乃懸浮有奈米粒子的液體，其吸引研究者注目的一項原因為其熱傳導係數會因小量粒子的加入而明顯上升，但其機制至今仍未全面明朗。本論文的工作先以暫態熱線法與惠斯通電橋建構實驗架構、並加以驗證，再對以二氧化鈦奈米粒子與去離子水合成的奈米流體進行多項參數下熱傳導係數的量測，共獲致如下結果。改變奈米流體的單體粒子尺寸並不會明顯提高其熱傳導係數；在低體積濃度下，奈米粒子加入之濃度會明顯增加熱傳導係數；奈米流體容易受到老化效應之影響，其熱傳導係數之增益量隨時間而逐漸遞減，其主因為出現群聚之現象所致；當奈米流體的酸鹼值到達近等電位點時，其奈米粒子周圍電雙層之效應會被消除，而使其熱傳導係數達最高值。

Nanofluid is a liquid suspended with nano-sized particles. It attracts many researchers because the heat conductivity of nanofluids can be enhanced significantly by adding a tiny amount of nano particles into the liquid. However, the mechanisms for the enhancement are still not fully understood. An experimental apparatus was built successfully in this thesis using transient hot wire method incorporated with Wheatstone bridge. The apparatus was validated and applied to measuring the heat conductivity of -water nanofluids for a variety of parameters. The main findings are as follows. The heat conductivity of nanofluids depends weakly on the monomer size, but increases significantly with the volume fraction of the nanofluids, provided the volume fraction is sufficiently low. Aging effect is significant, which reduces the heat conductivity with time because of the agglomeration of particles. The heat conductivity is maximized when the PH value meets the isoelectric point of the nanofluid.