指導教授：李雨臺灣大學：應用力學研究所葉星毅Yeh, Hshing-IHshing-IYeh2014-11-302018-06-292014-11-302018-06-292014http://ntur.lib.ntu.edu.tw//handle/246246/264103奈米流體為具均勻分散及穩定懸浮奈米粒子的懸浮液。據文獻報告其熱傳導係數明顯高於其基底液體者及傳統理論預測值，但其機制並未完全明瞭。此現象可望應用在熱交換器上，而其中泵之輸出功率由冷卻液的黏度主導。因此奈米流體的黏度亦為相關研究的重點、且為本文之研究目標。本文以二氧化鈦奈米粒子加入水或甘油等基底流體中來合成奈米流體，對其進行黏度的實驗研究，共獲致如下結果：(i)在所探討的參數範圍內，奈米流體是牛頓流體。(ii)黏度隨著粒子體積濃度的增加而上升、隨著粒子粒徑的下降而上升、及隨著溫度的增加而下降；但相對黏度(奈米流體黏度與基底液體黏度的比值)卻不隨溫度的改變而改變，顯示奈米流體與基底液體隨溫度的改變定性相同，但在定量上粒子粒徑愈小、且基底液體愈不黏者，因布朗效應愈強故其相對黏度愈大；另體積濃度愈高，愈多粒子參予布朗效應，而使相對黏度也愈高。(iii)奈米流體黏度會隨基底液體的導電率增加而上升，至其pH值達等電位點(約pH = 6)時，黏度達到峰值、而約為基底液體黏度的240倍，pH值超過等電位點後，黏度會迅速下降。上述現象可用因電雙層效應引致的粒子間庫倫斥力弱化或消失、而導致粒子迅速聚集來作解釋。(iv) 黏度隨放置時間之增加而略降，此一老化效應在較高體積濃度時才比較明顯，如體積濃度為4%時，放置一週後其黏度約下降10%。Nanofluid is a liquid suspended with uniformly distributed and stable nano-sized particles. The heat conductivity of nanofluid is substantially higher than that of its base fluid and the classical theoretical prediction according to the literature, but the mechanisms are still not fully understood. Such a heat conductivity enhancement implies that nanofluids can be applied to heat exchangers. However, the pumping power of nanofluids in heat exchanger depends on its viscosity, which is also one of the major topics of nanofluid research, and is also the goal of the present thesis. The nanofluids of the present study are made by introducing TiO2 nano particles into de-ionized water or glycerol. Viscosity measurements were performed and the results are summarized as follows: (i) Nanofluids are Newtonian fluids in the parameter ranges of the present study. (ii) The viscosity of nanofluid increases as the particle’s volume fraction increases, as the particle size decreases, and as the temperature decreases. On the other hand, the relative viscosity (the ratio between the nanofluid viscosity and the base fluid viscosity) remains essentially invariant with temperature, implying that the temperature variation of nanofluid viscosity is qualitatively similar to that of base fluid. However, the relative viscosity of nanofluid is larger for case with smaller particles and with less viscous base fluid, because of the stronger Brownian effect. Also the relative viscosity is larger for higher volume fraction as more particles participates the Brownain effect. (iii) The nanofluid viscosity increases with the base fluid electric conductivity, and reaches its maximum value (about 240 times the viscosity of the base fluid) at an electric conductivity corresponds to the isoelectric point (when pH = 6 approximately). The viscosity decreases rapidly as the pH value increases further above the isoelectric point. The above phenomena can be explained by the particle agglomeration effect associated with the weakening of the Coulomb’s repulsive force between electric double layers of two particles. (iv) The viscosity decreases slightly as times goes by. Such an aging effect becomes moderate at higher volume fraction. For example, the viscosity decreases about 10% after a week for a nanofluid with volume fraction 4%.致謝 II 摘要 III Abstract IV 第一章 緒論 1 1-1 研究背景 1 1-2研究目的與動機 2 1-3文獻回顧 2 1-4文本架構 4 第二章 原理 5 2-1 黏度計測量原理 5 2-2 導電率計之測量原理 7 2-3 pH值計之測量原理 8 2-4 懸浮液的黏度 8 2-5 電雙層 9 2-6等效顆粒 11 第三章 研究方法與實驗步驟 13 3-1奈米流體的調配 13 3-2 改變基底流體之導電率 14 3-3 改變基底流體之pH值 15 3-4流體性質量測之實驗步驟 16 3-4-1 奈米流體之流變性質 17 3-4-2 體積分率、顆粒大小以及溫度的影響 17 3-4-3改變基底流體導電率之奈米流體黏度與導電率測量 18 3-4-4改變基底流體pH質之奈米流體黏度與導電率測量 19 3-4-5老化效應(Aging effect) 19 第四章 研究結果與討論 20 4-1 以去離子水為基底之奈米流體之流變性質 20 4-2 以去離子水為基底之奈米流體之體積分率、顆粒大小及溫度對黏度及導電率的影響 20 4-3以甘油為基底流體之奈米流體之流變性質與體積分率、顆粒大小以及溫度對黏度的影響 21 4-4改變基底流體導電率與酸鹼度之奈米流體黏度與導電率測量 22 4-4 老化效應(Aging effect) 24 第五章 結論及未來展望 25 5-1 結論 25 5-2 未來展望 26 參考書目 271630945 bytesapplication/pdf論文公開時間：2016/08/21論文使用權限：同意有償授權(權利金給回饋本人)二氧化鈦奈米流體黏度導電率布朗運動電雙層thesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/264103/1/ntu-103-R01543072-1.pdf