本研究係程式模擬懸浮液在圓管中的熱傳表現做為起始值評估，接著以實驗的方式探討實際的狀況，先將粒徑約180到200奈米之24烷微粒懸浮於基底流體為純水中，形成奈米乳液；並透過DLS、黏度計、密度計、DSC等儀器量測其熱物性質包含粒徑、密度、黏度、熱傳導係數、比熱等。然後，利用初步模擬乳液於圓管內熔解率變化，以作為實驗數據解釋之依據。並利用24烷奈米乳液取代純水當作工作流體，探討其應用在等熱通量加熱的水平圓管內層流強制對流熱傳遞的特性及效益。在熱傳實驗中所使用圓管係長度1300mm，內徑3.5mm，外徑4mm的銅管，並在其測試段外管壁面加熱段部分纏繞鎳鉻電阻線以達等熱通量的加熱條件。熱傳遞實驗所設定相關條件為：管內工作流體之進口溫度45ºC，進口流量為60 cm3/min、90 cm3/min、120 cm3/mi及180 cm3/min，加熱功率為30W、40W、50W、60W，奈米乳液內含相變化材料的質量分率為2%、5%及10%。熱傳遞實驗所得結果顯示，在合適的流量及加熱功率下，奈米乳液可以有效降低管壁溫度，並提升平均熱傳遞增益；相較於純水，其最大壁溫壓抑增益與平均熱傳增益可分別達13.87%與9.8%。另外，以24烷奈米乳液取代純水為圓管內層流強制對流熱傳遞流體之效能指標FOM最高值大約僅1.034。添加石墨烯奈米流體後，由於會和奈米乳液產生聚集的現象，故其並非隨著濃度提升產生較佳的熱傳增益，反而在較低濃度的部分熔解完的相變化乳液可以藉由石墨烯略為提升熱傳導係數，在平均熱傳增益方面最高增益為約略9%，而由於添加的石墨烯濃度僅0.006%，在壓降部分提升較少，使得FOM值最高可以達到1.07左右。

The present study aims to explore, via heat transfer experiments complementary with numerical simulations, the forced convective effectiveness of using water-based hybrid nanofluid of nanoemulsion of a phace change(Nano-PCM particles) and graphene nanoparticles, instead of the pure water, in an iso-flux heated horizontal circular tube. The phase change material adopted for preparing the nano-PCM emulsion is Tetracosane Thermophysical properties of the water-based hybrid nanofluids formulated, such as the particle size, the density, the dynamic viscosity, the thermal conductivity and the specific heat, were first measured by employing DLS, a rotational viscometer, a vibrational density meter, and DSC, respectively.
A closed-loop forced convection experimental set-up was constructed with a copper circular tube of inner and outer diameters of 3.5 and 4.0 mm, respectively. An iso-flux heated section over the test tube was fabricated by winding nickel-chromium resistance wire along its outer surface over a length of 1300 mm. The internal forced convection experiments have been performed for the pure water and the hybrid nanofluids formulated under the following conditions of the pertinent variables/parameters: the inlet fluid temperature equal to Tin = 45C; the volumetric flow rate, Q = 60, 90, 120, and 180 cm3/min; the heating power, qo = 30, 40, 50W; and the mass fraction of Tetracosane PCM nanoparticles and the graphene nanoparticles dispersed in hybrid nanofluids, pcm = 2, 5, 10% and np =0, 0.006%, respectively.
The heat transfer experimental results show that under appropriate flow rate and heating power, using the pure phase change nano-emulsion to replace the water as the heat fluid can effectively reduce the wall temperature more than 13% and thus enhance the heat dissipation effectiveness up to 9.8%. However, the highly increased viscosity of the phase change nano-emulsions formulated appears drastically downgraded its highest figure of merit (FOM) of only about 1.034 for its forced convective cooling performance. Further adding graphene nanoparticles in phase change nano-emulsion to form the hybrid nanofluid, the results from corresponding forced convection experiments indicate that significant heat transfer enhance of about 9% can arise for the hybrid nanofluid containing graphene of np = 0.006% and the nano-PCM particles of pcm = 5%. Meanwhile, the corresponding FOM value for such hybrid nanofluid appears uplift to about 1.07.

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