本文採實驗方式針對具毫米流道熱沉與熱源之矩形自然對流迴路，探討在等溫加熱及等溫冷卻條件下，以氧化鋁-水奈米流體取代純水之熱傳遞特性及效益。實驗迴路之熱沉與熱源段係以紅銅材質製作，分別具34 與23流道之毫米熱交換器，兩者之流道水力直徑均為0.96 mm 而絕熱段則採用內管徑為4 mm之壓克力圓管。本文所使用之氧化鋁-水奈米流體，其內含氧化鋁微粒之質量分率介於0 ~ 1.0 wt.%。熱傳實驗係透過加熱片及恆溫槽分別控制熱源與熱沉段之溫度設定，藉其間溫差形成浮力驅動迴路內自然對流輸送現象，測定迴路內毫米流道熱沉與熱源之進出口溫度與絕熱段溫度分佈，進而測定毫米流道熱沉與熱源之平均熱傳係數、熱阻與迴路之自然對流質流量。本研究之實驗結果顯示，利用氧化鋁-水奈米流體取代純水可有效地提升矩形自然對流迴路熱傳遞效率，最高可提升約20%的熱傳量；而在系統熱阻方面，添加1.0wt%的奈米流體，最多可降低約14.3%。另一方面，由於氧化鋁-水奈米流體黏滯係數相較於純水隨其質量分率呈現顯著上升趨勢，導致迴路內流動量或雷諾數亦隨之明顯下降。

In this study, effectiveness of using alumina/water nanofluid to replace the pure water as the working fluid in a rectangular natural circulation loop with millimeter heatsink and heatsource has been investigated experimentally. The heatsink and heatsource sections of the circulation loop were fabricated using oxygen-free copper with 34 and 23 minichannels, respectively, which have identical hydraulic diameter of 0.96 mm. The adiabatic sections of the circulation loop were constructed by means of Acrylic circular tubes of 4mm in inner diameter. The alumina/water nanofluids used in the experiments contain various mass fraction of alumina nanoparticles between 0 ~ 1.0 wt.%. During the experiments, the heating and cooling sections of the loop were isothermally heated and cooled by means of a DC power supply and a constant-temperature bath, respectively. The experimental results clearly show that the heat transfer effectiveness can be significantly upgraded by using the alumina/water nanofluid to replace the pure water in the rectangular natural circulation loop with minichannel heat exchangers.

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