奈米流體之熱傳效能分析

An Analysis of the Heat Transfer Performance of Nanofluids

徐健力(Cheng-Li Hsu)

指導教授 ： 許政行

中原大學/工學院/機械工程研究所/碩士(2002年)

https://doi.org/10.6840/cycu200200339

摘要

在工業應用上，發展具有能量效益(Energy-Efficient)的熱傳流體，一直存在著熱傳效能偏低的問題。為了克服這個限制，工業界發展出一套新的技術，那就是在液體，例如水或油裡，加入懸浮的結晶奈米粒子(Suspending Nanocrystalline Particles)，在液體中加入的極小奈米粒子改變了液體原本的熱傳性質與熱傳效能，這顯示了此種液體在增加熱傳方面具備了很高的潛力，這種液體就是我們現在所說的「奈米流體」
(Nanofluids)。在本篇論文中，我們將分析奈米流體的熱傳效能，並探討幾個影響熱傳效能的因素，例如奈米粒子的體積比率(Volume Fraction)、外表(Shape)、尺寸(Size)及性質(Properties)，以及推導出在等溫壁及等熱通量的流場中，考慮軸向和徑向熱傳及忽略軸向熱傳共四個不同的條件下，預測奈米流體熱傳效能的基礎方程式。我們可以發現奈米流體的熱傳表現之所以會比一般流體好的原因，不只是因為它的高熱傳係數，奈米粒子無規則的運動及擴散效應也是增加奈米流體熱傳效能的原因之一，我們可由Peclet number(Pe)來描述這些因素的影響。由Nu對Pe的關係圖可以得知，若Pe愈大則Nu隨著變大，也就是說流體的Pe愈大熱傳效能也愈好。

關鍵字

奈米流體 ； 那左數 ； 奈米粒子 ； 倍力數

並列摘要

Low thermal conductivity is a primary limitation in the development of energy-efficient heat transfer fluids required in many industrial applications. To overcome this limitation, a new class of heat transfer fluids is being developed by suspending nanocrystalline particles in liquids such as water or oil. The resulting “nanofluids” possess extremely high thermal conductivities compared to the liquids without dispersed nanocrystalline particles. In this paper, we will analysis the performance of the nanofluids, and research some factors that affect the performance of the nanofluids, for example, the volume fraction、size、shape、properties etc. We also introduce the fundamental equation of 4 individual situations that can predict the heat transfer performance of the nanofluids, including with axial and radial heat transfer and without axial heat transfer. We can find that the performance of the nanofluids is better than that of the normal fluids, not only because it’s high thermal coefficient but also because the random movement and dispersion of the nanocrystalline. We can use the Peclet number to describe the affect of these factors and find that Nusselt number is increasing with Peclet number, that is, the higher the Peclet number of the nanofluids is the better the performance of heat transfer will be.

並列關鍵字

Nusselt number ； nanofluids ； nanocrystalline ； Peclet number

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