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Title: | 二氧化鈦奈米流體黏滯性質的實驗探討 Experimental Study of Viscosity of Titanium Oxide Nanofluids |
Authors: | Hshing-I Yeh 葉星毅 |
Advisor: | 李雨(U Lei) |
Keyword: | 二氧化鈦,奈米流體,黏度,導電率,布朗運動,電雙層, TiO2,nanofluids,viscosity,electrical conductivity,Brownian motion,Electrical double layer, |
Publication Year : | 2014 |
Degree: | 碩士 |
Abstract: | 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%. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/56613 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 應用力學研究所 |
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