三氧化二鋁奈米流體熱性質分析 與實驗研究

Analysis and Experimental Research on Al2O3 Nanofluids of Thermal Properties

郭育廷(Yu-Ting Kuo)

指導教授 ： 卓清松

國立臺北科技大學/機電學院/冷凍空調工程系所/碩士(2006年)

摘要

本研究使用以直接混合製備方式來獲得三氧化二鋁奈米流體，進行實驗分析探討添加三氧化二鋁奈米流體其熱傳導係數及熱對流係數。並將奈米流體實際應用於水冷式熱交換器及儲冷冰球，評估奈米流體應用於熱交換器及儲冷系統的可行性。研究結果發現：在奈米流體重量濃度影響方面，樣本溫度40℃時，0.1%wt能提升熱傳導係數2.5%，當重量濃度上升到2.0%wt時，則能上升到19.1%。在實驗樣本溫度影響方面，重量濃度2.0%wt時，樣本10℃時能提升熱傳導係數11.1%，當溫度上升到40℃時，則能上升到19.1%，因此不論重量濃度或者溫度對於熱傳導係數的增進率均呈現正比關係。在黏滯係數方面，奈米流體黏滯度隨濃度呈上升之趨勢，其流體仍然為牛頓流體。水冷式熱交換器應用方面，發現奈米流體之熱對流係數與熱傳導係數在相同溫度下亦會隨濃度上升而增加。結冰成核方面，在-11℃的冷卻條件下，實驗樣本為0.1%wt及0.5%wt的過冷度與水比較時皆有提升的趨勢，但1.0%wt時，過冷度卻較水低，因此0.5%wt實驗樣本是提升過冷度效能最佳濃度。而在-15℃冷卻條件之下，發現所有濃度過冷度都下降，且發現其過冷度趨向一致之現象。

關鍵字

奈米流體 ； 熱傳導係數 ； 過冷度

並列摘要

This study investigates the relationship between thermal conductivity and heat convention of aluminum oxide nanofluids. The samples of aluminum oxide nanofluids are prepared by two step method. The aluminum oxide nanofluids apply to water-cooled heat exchanger and ice nucleation. In order to estimate the application of the heat exchanger and the feasibility of ice capsules in thermal storage system.
The experimental results showed when sample temperature was set at 40℃, an increase in weight fraction of Al2O3 nanoparticles from 0.1%wt to 2.0%wt can increase the enhanced thermal conductivity ratio from 2.5% to 19.1%. Similarly, when the concentration of sample was set at 2.0%wt, an increase in sample temperature of Al2O3 nanoparticles from 10℃ to 40℃ can increase the enhanced thermal conductivity ratio from 11.1% to 19.1%Therefore, both the weight fraction and sample temperature of nanofluids are linearly related to thermal conductivity. The viscosity of the Al2O3 nanofluids with the raising concentration can be regarded as Newtonian fluid.
The aluminum oxide nanofluids apply in the water-cooled heat exchanger. Experimental results show that the heat convection and the thermal conductivity are enhanced with the concentration of sample at a fixed temperature. Results of ice nucleation, when the concentration of sample was set at 0.1%wt and 0.5%wt , the subcooling were enhanced compared with water when temperature set at -11℃, the subcooling were lower than water at 1.0%wt. Therefore, the 0.5% wt experiment samples on subcooling efficiency is the best concentration. The temperature of sample at -15℃, when water, 0.1%wt, 0.5%wt and 1.0%wt subcooling were drop to consistent phenomenon.

並列關鍵字

nanofluids, ； thermal conductivity ； subcooling

參考文獻

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