本研究係以實驗的方式，先將粒徑約70到100奈米之23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，針對23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3.4mm，外徑4mm的銅管，並在其測試段外管壁面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分別為30 ºC及38ºC，進口流量為12.5 cm3/min、24 cm3/min、60 cm3/min及120 cm3/min，加熱功率為20W、30W、40W、50W，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18%與14%。另外，由於奈米乳液具遠較純水為高之黏滯係數，導致其壓降大幅上升，最高增幅可達2.8倍；因此，以23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1.07。

In the present study, laminar forced convection heat transfer characteristics of water-based nanoemulsion of PCM (Tricosane) in an iso-flux heated circular tube were experimentally investigated. Thermophysical properties of the water-based PCM nanoemulsion 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. In the forced convection heat transfer experiment performed, a circular copper tube of inner and outer diameter 3.4 and 4.0 mm with a length of 1300 mm was iso-flux heated by wrapping nichrome resistance wire over a section of 400 mm. The internal forced convection experiments have been performed under the following conditions for the pertinent variables/parameters: the inlet fluid temperature, Tin = 30 and 38 C; the volumetric flow rate, = 12.5, 24, 60, and 120 cm3/min; the heating power, = 20, 30, 40W; and the mass fraction of Tricosane dispersed in the PCM nanoemulsion, = 2, 5 and 10%. The heat transfer results obtained clearly reveal that by replacing the pure water with the water-based PCM nanoemulsion as the heat transfer medium, the wall temperature of iso-flux heated tube can be suppressed effectively and the averaged heat transfer coefficient over the heated section appears significantly enhanced, leading to a reduction in the tube wall temperature of 14% and an enhancement of 18% in the averaged heat transfer coefficient, respectively, in comparison with that of the pure water. On the other hand, resulted from its greatly increase in the dynamic viscosity relative to the pure water, the pressure drop arisen for the PCM nanoemulsion flow in the tube was found drastically uplifted, may leading to an increase of 1.8 times in the pressure drop over that of the pure water. As a result, the figure of merit (FOM) of using the water-based PCM nanoemulsion formulated over the pure water for the laminar forced convection in the circular tube was found up to 1.07 at best.

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