本研究以純水為工作流體，針對由上層毫米流道與下層微米流道構成之疊置雙層熱沉，探討反向流配置下之三維穩態共軛熱傳與流動特性，並以同向流作為比較基準。數值模型同時考量固體導熱與上、下層流體對流，採有限體積法離散統御方程式。經預分析結果顯示，熱浮力對主要溫度與熱傳結果之影響有限，故後續參數研究採完全發展速度場求解穩態能量方程式。本文以入口溫度30℃為主要分析條件，探討下層雷諾數為500、1000與2000，以及不同上、下層體積流量比對熱散逸特性之影響。另選取入口溫度50℃進行不同入口溫度條件之比較。各操作條件之加熱面熱通量以加熱面最高溫度不超過85℃為設定原則。
結果顯示，反向流使上、下層流體由流道兩端進入，局部冷卻能力沿軸向呈互補分布。隨下層雷諾數增加，加熱面與流道壁面溫度降低，平均總紐賽數及下層平均熱對流係數提高，最大與平均熱阻則下降。固定下層雷諾數時，下層平均熱對流係數受上層流量影響有限，而上層平均熱對流係數隨上、下層體積流量比增加而提高，惟下層微米流道仍為主要熱移除通道及主要流動阻力來源。
同向流與反向流比較結果顯示，反向流可使加熱面溫度均勻度改善約2.3%∼3.2%，並於低至中等體積流量比下，降低加熱面最高溫度，最大降幅約為3%。然而，在較高流量比下，其最高溫度與整體熱傳性能未必優於同向流。
綜合而言，本文評估不同雷諾數下之熱負載能力，並釐清上、下層流量分配與流向配置對熱傳與溫度均勻度之影響。結果顯示，反向流之主要效益在於改善加熱面溫度均勻度與熱點分布，而非全面提升平均熱傳性能，可作為高熱通量電子元件散熱系統之設計參考。

This study numerically investigates the three-dimensional steady conjugate heat transfer characteristics of a stacked double-layer heat sink consisting of an upper mini-channel and a lower microchannel, with pure water used as the coolant in both layers. Countercurrent flow is adopted as the primary configuration and compared with co-current flow under identical geometry, flow, and heating conditions. The governing equations are discretized by the finite volume method. After thermal buoyancy was found to have only a minor influence on the main thermal results, the parametric study was conducted using fully developed velocity fields and steady energy equations. The inlet temperatures are 30 and 50 °C, the lower-layer Reynolds numbers are 500, 1000, and 2000, and the upper-layer Reynolds number is varied to generate different upper-to-lower volumetric flow-rate ratios. Results show that the lower microchannel remains the dominant heat-removal path, while the upper mini-channel mainly provides auxiliary cooling and redistributes the axial thermal load. Countercurrent flow improves heated-surface temperature uniformity by about 2.3–3.2% and reduces the maximum temperature by up to about 3% at low-to-moderate flow-rate ratios. However, its overall heat transfer coefficient is not necessarily higher than that of co-current flow. Countercurrent flow is therefore more effective for temperature homogenization and hotspot control than for universal enhancement of average heat-transfer performance.

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