二氧化鈦奈米流體熱性質與應用研究

Research of Thermal Property and Application for TiO2 Nanofluids

賴耒聲(Lei-Sheng Lai)

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(2007年)

https://doi.org/10.6841/NTUT.2007.00051

摘要

本研究使用直接混合法製備二氧化鈦/水奈米流體，並以實驗研究法探討二氧化鈦奈米流體在不同濃度與溫度條件之下，其熱傳導係數、黏滯係數、密度及熱對流係數的變化，最後並實際應用於氣冷式熱交換器及量測流體之結冰成核溫度，藉以評估奈米流體應用於冷凍空調領域之可行性。研究結果發現：熱傳導係數在溫度40℃與重量濃度2.0%wt時，熱傳導係數提升3.4%，濃度影響熱傳導係數較溫度影響為高。在流體密度量測方面，濃度與流體之密度皆為線性的正比關係，溫度對奈米流體的密度影響較不明顯。在黏滯係數量測方面，可發現本研究所使用的二氧化鈦奈米流體屬於牛頓流體，濃度與黏滯係數呈現非線性正比關係，與溫度呈現反比關係，整個實驗條件範圍之下，最大增進率為21%。在熱對流係數量測方面，添加奈米顆粒濃度與與熱對流係數呈現非線性的反比關係，呈現不利於熱傳的結果。在氣冷式熱交換器應用方面，實驗結果發現在層流與紊流流動下，添加奈米顆粒能有效的提升去離子水之熱交換量，而且有隨著濃度增加而增加的趨勢，最大熱交換量增進率高達65.6%，這個研究結果與熱對流係數實驗結果相反，主要的原因是熱交換器結構的關係，奈米流體在低流速的狀態之下的稀薄黏滯效應所致。在結冰成核溫度量測方面，0.5%wt重量濃度能有效的提升流體之過冷卻溫度，濃度高於0.5%wt時反而會使過冷卻溫度降低。
本研究針對二氧化鈦奈米流體進行相關實驗研究，主要的貢獻除了在於確認其基礎熱性質之外，更在熱交換與過冷卻溫度的實驗研究中發現熱交換器結構會影響奈米流體在熱傳性能上的表現以及過冷卻溫度變化的臨界點。上述研究成果希望能對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 ； 熱傳導係數 ； 黏滯係數 ； 熱對流係數

並列摘要

The study uses two-step method to make and prepare TiO2/water nanofluids, and employs experimental research method to investigate the changes in the thermal conductivity, viscosity, density and heat convection coefficient of TiO2 nanofluids under different weight fractions and different temperature conditions. Finally, the study practically applies them to the air-cooled heat exchanger and the ice nucleation temperature of the measured fluids, so as to evaluate the feasibility of applying nanofluids to the domain of air conditioning and refrigeration. The results show that when the temperature is 40oC and the concentration is 2.0%wt, the thermal conductivity rises by 3.4%. The influence of concentration on thermal conductivity is higher than the influence of temperature. For the measurement of the density of fluids, the concentration and the density of fluids are in linear positive proportional relationship. The influence of temperature on the density of nanofluids is not so obvious. As to the measurement of viscosity, it is found that the TiO2 nanofluids used by the study belong to the Newtonian fluid. Its concentration forms a non-linear positive proportional relationship with its viscosity, and forms an inverse proportional relationship with temperature. Within the entire scope of experimental conditions, the maximum increment is 21%. As to the measurement of heat convection coefficient, the concentration of the added nanoparticles forms a non-linear inverse proportional relationship with the heat convection coefficient, which is a result disadvantageous to heat transfer. As to the application of air-cooled heat exchanger, the experimental results show that under laminar and turbulent flow, the addition of nanoparticles can effectively increase the heat exchange quantity of deionized water. With the trend of increase along with the increase of concentration, the maximum increment of heat exchange quantity is as high as 65.6%. This research result is opposite to the experimental result of heat convection coefficient. This is mainly due to the shear thinning effect of nanofluids at low flowing speed under the structure of heat exchanger. As for the measurement of ice nucleation temperature, the weight fraction of 0.5%wt can effectively raise the excessive cooling temperature of fluids, but the weight fraction of above 0.5%wt would contrarily reduce the excessive cooling temperature of fluids.
The study undergoes the related experimental research focusing on TiO2 nanofluids. Not only contributive to the confirmation of its thermal properties, the study also discovers in the experimental researches of heat exchange and excessive cooling temperature that the structure of heat exchanger would influence the heat transfer performance of nanofluids as well as the marginal point for the change of excessive cooling temperature. It is hoped that the above research results are referential to the researchers conducting the related studies of the heat transfer of nanofluids.

並列關鍵字

nanofluids ； thermal conductivity ； viscosity ； heat transfer coefficient

參考文獻

[17] 洪忠仁，氧化銅奈米流體熱性質分析與應用研究，碩士論文，國立台北科技大學冷凍空調工程研究所，台北，2005。

[1] R. P. Feynman, "There's Plenty of Room at the Bottom," Journal of Microelectromechanical Systems, vol. 1, no. 1, 1992, pp.60-66.

[3] H. Froes and C. Suryanarayana, "Nanocrystalline metals for structural applications," Journal of metals, vol.41, no. 6, 1989, pp.12-17.

[4] L. D. Chang and C. M. Mou, "Nanomaterials and Nanostructure," Peking: Science Press, 2001.

[5] R. Birringer, "Nanocrystalline Materials," Materials Science and Engineering , vol. A117, no. 1-2, 1989, pp. 33-43.