奈米流體熱性質與熱儲存性能之研究

Investigation of Thermal Properties and Thermal Storage Performance for Nanofluids

許育菁(Yu-Jing Shiu)

指導教授 ： 卓清松

國立臺北科技大學/機電學院/能源與冷凍空調工程系碩士班/碩士(2008年)

摘要

本研究使用二階合成法製備乙二醇系的三氧化二鋁(Al2O3/EG)與銅(Cu/EG)奈米流體，並以實驗研究法探討奈米流體在不同濃度與溫度條件之下，對其熱傳導係數、黏滯係數及流體密度的影響。並藉由熱對流性質量測實驗以瞭解奈米流體在管路中的壓降狀態及與總熱傳係數，最後利用冰球儲冷特性實驗，對於奈米流體應用於儲冰系統的可行性與性能進行評估。在熱傳導係數量測方面，以Cu/EG奈米流體的熱傳增進效果為最佳，在溫度30℃與重量濃度0.75%wt時，熱傳導係數可提升19.16%。在流體密度量測方面，濃度與流體密度皆呈現非線性的正比趨勢，且粒徑大小對於奈米流體密度的影響並不明顯。在黏滯係數量測方面，可以發現本研究所使用的奈米流體皆屬於牛頓流體，濃度與黏滯係數的關係皆呈現非線性正比趨勢，與溫度成反比的趨勢。在熱對流性質量測方面，若能改善奈米流體的懸浮性將能得到更加的熱傳效果，在本實驗-3℃的條件下，總熱傳係數最多可提升14.15%；15∼50℃的範圍下，對流係數最多可提升15.19%。而奈米流體於管路中的壓降情形與濃度、流量成正比關係，與溫度成反比關係，並確認傳統的壓降估算方程式無法準確預測奈米流體在管路中的壓降狀態。在冰球特性實驗應用研究方面，使用傳統鹵水要使單顆冰球結冰所需的時間大約需要3-4小時。而改用奈米流體後，在本研究所設定的條件下，最多可縮短12.8%的儲冰時間，因此可以預期未來在儲冰系統的實際使用上將可望達到節能與降低運轉費用與更佳的運轉效益。
本論文針對奈米流體進行相關基礎特性與應用的實驗研究，主要的貢獻除了在研究乙二醇系奈米流體在不同粒徑與材料的條件下，對其基本性質的比較外，更確認了奈米流體應用在儲冰系統上的可行性，上述研究成果希望能提供奈米流體熱傳領域的研究者進行相關研究時參考。

關鍵字

奈米流體 ； 熱儲存 ； 三氧化二鋁 ； 銅 ； 乙二醇

並列摘要

The study used two-step synthesis to prepare ethylene glycol based nanofluids with alumina (Al2O3/EG) and copper (Cu/EG) nanoparticles, and employed experimental research method to investigate the influence of nanofluid on its thermal conductivity coefficient, viscosity coefficient and fluid density under the conditions of different concentrations and temperatures. Through the measurement experiment of the thermal convection nature, the study understood the pressure reduction situation of nanofluids in the pipe, and obtained the thermal convection coefficient. Finally, through the experiment of coldness storage by ice-balls, the study evaluated the feasibility and performance of the application of nanofluids to ice storage system. Regarding the measurement of thermal conductivity coefficient, Cu/EG nanofluid has the best incremental effect of thermal conductivity. When the temperature is 30℃ and the weight concentration is 0.75% wt., the thermal conductivity coefficient can be enhanced by 19.16%. For the measurement of fluid density, there appears a non-linear positive proportion between concentration and fluid density. Besides, particle size does not have obvious influence on the density of nanofluid. As to the measurement of viscosity coefficient, it is found that all the nanofluids used by the study belong to Newtonian fluid. There is the trend of a non-linear positive proportion between concentration and viscosity coefficient, and the trend of an inverse proportion between concentration and temperature. Regarding the measurement of thermal convection nature, if the suspension performance of nanofluid can be improved, a better thermal convection effect can be achieved. In this experiment, under the temperature condition of -3℃, the thermal convection coefficient can be increased by 14.15%.Within the range of 15∼50℃, the convection coefficient can be increased by 15.19% maximum. The pressure reduction of nanofluid in the pipe is positively proportional to concentration and flow, but inversely proportional to temperature. The traditional estimation equation of pressure reduction cannot accurately predict the pressure reduction situation of nanofluid inside the pipe. As to the experiment of ice-ball properties for application research, it takes around 3-4 hours to make a single frozen ice-ball by using the traditional brine. After the use of brine is changed to be nanofluid, under the conditions preset by the study, the ice storage time can be shortened by 12.8% maximum. Hence, it is predicted that the actual use of nanofluid in ice storage system in future will achieve the effects of energy conservation, reduction of operation expense, and better operation performance.
This research paper focused on nanofluid to carry out the experimental studies of the related foundational properties and application. The main contribution of the paper not only includes the comparison of the basic nature of nanofluids in ethylene glycol (EG) series during the research of these nanofluids under the conditions of different particle sizes and materials, but also confirms the feasibility of applying nanofluid to ice storage system. It is hoped that the above research results can provide a reference for the researchers studying the related realm of thermal conductivity of nanofluids.

並列關鍵字

nanofluids ； thermal storage ； alumina ； copper ； ethylene glycol

參考文獻

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