在流體裡面加入奈米粒子，並加入一些界面活性劑使奈米粒子可以均勻分散在流體裡面，稱之為奈米流體。由於奈米流體可以大幅增加流體的熱傳導係數，且隨著濃度的越高，其增加的熱傳導係數越大。本論文在探討一些奈米流體的熱傳導係數，有用化學還原法合成成奈米金水溶液，金的大小尺寸為20nm。也有測量奈米銀的水溶液。更進一步在水和乙二醇裡加入三氧化二鋁和氧化銅粒子，驗證其熱傳導係數有無增加和黏滯係數的增加量，並探討其熱傳增加的機制。
在奈米流體實驗的部分，利用暫態熱線法和穩態平行板法兩種方法來量測熱傳導係數。其中暫態熱線法量測儀器為自行組裝。探討濃度和熱傳導係數的關係，發覺在三氧化二鋁，氧化銅的奈米流體裡，熱傳導係數會隨著體積分率的增高而有所增加，且奈米氧化銅粒子較三氧化二鋁小，所以對增加流體的熱傳導係數的效果較為明顯。並利用改變酸性來增加三氧化二鋁在水中的分散性，發現有加酸的奈米流體分散較好，熱傳導係數較高，且黏滯係數較低。而在磁性流體方面，磁性流體的熱傳導係數變化會隨著磁場的增大而有所增加，但隨著磁性流體的達到飽和磁化，而不再增加；且隨著不一樣的磁場方向，熱傳導係數會跟著有所變化。

Nanofluid is a fluid of new type that consists of a base liquid with nanocrystalline particles dispersing in it. With the capability of higher thermal conductivity, the nanofluid has received considerable attention in related thermal management laboratories. In the present study, water and ethylene glycol are used as the base liquids respectively. The gold, silver, CuO and Al2O3 nanoparticles are added in the base liquids. Effects of volume fraction and size of nanoparticles on the viscosity and thermal conductivity of nanofluids are investigated by experiment. The thermal conductivity of nanofluids is measured by the steady-state parallel plate and transient hot-wire methods, respectively. Results here include (i) the homemade equipment to measure the effective thermal conductivity (ii) the measurement of thermal conductivity and viscosity (iii) the measurement of properties of nanofluids of various types. The results show that the thermal conductivity of the nanofluid increases with the volume fraction of the nanoparticles. Besides, the thermal conductivity of the nanofluids increases with decreasing the size of nanoparticles. In addition, the acid liquid is found to achieve a better dispersion of the nanoparticles in nanofluids. The better dispersion of nanoparticles also results in a lower viscosity and higher thermal conductivity of nanofluids. For ferrofluids, the thermal conductivity of ferrofluids increases with the strength of applied magnetic field. However, the thermal conductivity of the ferrofluid no longer increases as the applied magnetic field reaches a critical strength. The thermal conductivity of the ferrofluids varies with the direction of the magnetic fields. The data and the experience obtained in this work are significant for the research institutes to further develop the nano-technology.

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