本文數值研究模擬探討毫/微米流道疊置雙層熱沉系統與微米流道熱沉系統，流道內分別通入純水與機能性流體。主要分成兩部分進行微流道熱沉內共軛對流冷卻特性之探討，第一部分探討奈米乳液、奈米流體和純水於微米流道熱沉內的熱傳遞特性影響，第二部分探討毫/微米流道疊置雙層熱沉內分別以不同的流量比通入純水與機能性流體進行比較，觀察熱沉內的熱傳情形且探討是否能比單層微米流道有更高的散熱效益。流道內以擬渦度-速度法(Pseudovorticity-velocity)計算三維速度場，且以有限體積法進行數學離散。數值模擬所探討之相關參數與範圍為:入口溫度34 ，氧化鋁-水奈米流體體積濃度為1.0%、1.5%，相變化奈米乳液重量濃度為5%、10%，單層雷諾數為500~2000(總流量為12.19 ~52.05 )，底部熱通量為25~75 ，流量比分別為0.5、1.0、1.3、2.0、2.5及3.0。由數值模擬結果可知，毫/微米流道雙層疊置熱沉通入純水/純水時，與單層微米流道熱沉通入純水相比，壓降最大下降87.74%，熱散逸效能指標最大值為2.0975；通入純水/ 1.0%氧化鋁-水奈米流體時，與單層微米流道熱沉通入純水相比，熱散逸效能指標最大值為2.0567；通入純水/ 10%相變化奈米乳液時，與單層微米流道熱沉通入純水相比，熱散逸效能指標最大值為2.0424。
關鍵字:微米流道熱沉、疊置雙層矩形熱沉系統、氧化鋁-水奈米流體、相變化奈米乳液

In present study, the numerical researches are conducted to simulate the mini- and micro-channel stacked double-layer heat sink with pure water and functional fluids as the coolants which flow into channels respectively. The study is mainly divided into two parts to discuss. The first part discusses the influence of heat transfer characteristics between nano-PCM emulsion, nanofluid and pure water in microchannel heat sink. The second part discusses the comparison of pure water and functional fluids in different flow ratios of mini- and micro-channel stacked double-layer heat sink, and to observe the heat transfer situation in the heat sink and to explore whether it can have a higher heat dissipation effect than the single-layer microchannel heat sink. The three-dimensional velocity field in the channel is calculated by the pseudo-vorticity-velocity method, and use the finite volume method to discrete the mathematical formulas. The relevant parameters and ranges in the numerical simulation have been performed as follows : the inlet temperature, T_in=34℃; the volume fraction of alumina-water nanofluid is 1.0% and 1.5%; the mass fraction of nano-PCM(Phase Change Material) emulsion is 5% and 10%; the single-layer channel’s range of Reynolds number is 500~2000(equivalent to total flow 12.19~52.05(cm^3/min));the heat flux impose to bottom of the heat sink is 25,50and 75(W/cm^2); the ratio of flow rate for the heat sink is 0.5,1.0,1.3,2.0,2.5 and 3.0.
From the numerical simulation results, it reveals that when mini- and micro-channel stacked double-layer heat sink uses pure water/ pure water as the coolants, the pressure drop decreases by 87.74% as the ratio of flow rate is 3.0, and when the ratio of flow rate is 0.5, and the total flow rate is 38.77(cm^3/min),the overall heat transfer coefficient increases by 16.56% compared with single-layer heat sink. Moreover, when the ratio of flow rate is 0.5, the total flow rate is 38.77(cm^3/min), the overall heat transfer coefficient of the mini- and micro-channel stacked double-layer heat sink with pure water/1.5% volume fraction of alumina-water nanofluid as the coolants increases by 19.19% compared with single-layer heat sink with pure water as the coolants. Last but not least, when the ratio of flow rate is 0.5, the total flow rate is 25.48(cm^3/min), and the heat flux is 25(W/cm^2), the overall heat transfer coefficient of the mini- and micro-channel stacked double-layer heat sink with pure water/10% mass fraction of nano-PCM emulsion as the coolants increases by 36.14% compared with single-layer heat sink with pure water as the coolants.

Keywords: mini- and micro-channel stacked double-layer heat sink, microchannel heat sink, nano-PCM emulsion, nanofluid

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