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http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/17161
標題: | 微流道內奈米流體強制熱對流之實驗研究 Experiment on Forced Convection of Nanofluids in Micro Channel |
作者: | Yen-Ming Chen 陳妍名 |
指導教授: | 李雨 |
關鍵字: | 奈米流體,強制熱對流實驗,微流道,二氧化鈦, nanofluids,forced convection experiments,micro channels,TiO2, |
出版年 : | 2012 |
學位: | 碩士 |
摘要: | 奈米流體為液體溶液中懸浮有奈米顆粒的流體,其在熱傳導係數的增益方面多數文獻皆有明顯正面效應,其於傳統的強制對流實驗也有相當不錯之結果,但也有學者研究指出添加奈米顆粒對於熱對流係數有損無增的情形發生,而在自然對流實驗方面,許多研究都指出奈米液體的熱傳率相對於基底溶液有增有減,因而對奈米流體的力學與熱傳機制更添神秘面紗。多數研究認為奈米溶液在一定範圍體積分率內,其熱傳效果隨著濃度提升而增加,另外使用粒子之半徑越小越好,但這大多屬於理論分析之結論,實驗上仍有許多研究空間。本文擬以實驗方法在微流道內進行實驗,以增進了解奈米流體在微流系統中的應用。
本實驗利用微機電製程,製造出高寬為 50 x 50 um2、100 x 100 um2、及 100 x 1000 um2,長度皆為 17.5 mm 之微流道,以研究在不同雷諾數(Re = 0.6~18)、不同加熱功率與不同奈米溶液濃度(Phi = 0%, 0.6%, 1.2%, 1.8%)下的熱傳效果。微流道以PDMS 建置在一矽晶圓加熱基板上,在流道兩旁鋪有加熱電極,流道底部則建有五組測溫電極,以量測流道底壁溫度,另流道進出口皆有熱偶感溫線量測液溫。 實驗結果發現此裝置近似於等壁溫加熱, 使用粒子平均半徑為 19.7~101.1 nm 之二氧化鈦奈米溶液,其整體微流道系統熱對流係數會隨著雷諾數增加而提高,其濃度與熱對流係數之間無規律性。而就提高施加功率來說,整體系統的熱對流係數影響不大。 Nanofluid is a liquid suspended with nano particles. According to the literature, the heat conductivity of nanofluid is increased significantly in comparing with their base fluid. Forced convection is also enhanced for most of the reports, but there is a considerable amount of literature indicates that the heat transfer cannot be enhanced by using nanofluids in natural convection. It is general reported that the heat transfer enhancement is increased as the concentration of the particle increases and as the size of the particles decreases when the volume fraction of the particles is within certain range. The present study aims to study experimentally the convective heat transfer of nanofluids in micro channels. Micro channels with length 17.5 mm and cross sections 50 um x 50 um, 100 um x 100 um and 100 um x 1000 um were fabricated on silicon substrate using MEMS techniques. The top and the side walls were moulded with PDMS with two cylindrical reservoirs on both ends of the channels. Two heating electrodes were fabricated on the bottom walls of the channel for temperature measurement. The inlet and outlet fluid temperature were also measured using thermocouples. According to the experiment, the thermal boundary condition for the present micro device can be approximated as constant temperature for the bottom wall with the rest walls insulated. De-ionized water (the base fluid) and nanofluids (de-ionized water suspended with 0.6%, 1.2% and 1.8% nano sized TiO2 particles) were employed for the experiments. It was found that the heat transfer coefficient of the system increases linearly with Reynolds number for all the cases, but the heat transfer IV enhancement associated with nanofluids was not clearly observed. The heat transfer coefficient is essentially independent of the power input. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/17161 |
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顯示於系所單位: | 應用力學研究所 |
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