本文利用數值模擬探討直立毫/微米流道疊置雙層熱沉系統之共軛對流熱散逸特性，核心目的在於降低冷卻系統之泵浦功耗，創新地引入熱浮力效應以改善流道壓降，透過浮力誘發輔助流與調控邊界層特性，在維持微流道高散熱優勢的前提下，有效抑制流體阻力。為確保數值模型精準貼合實際應用，入口邊界條件採用均勻流條件，以真實還原入口效應與熱邊界層發展過程。
本研究內容分為兩部分：第一部分綜合探討入口速度場分佈與熱浮力效應對流道內熱傳與壓降特性之影響；第二部分建構毫/微米疊置結構之數學模型並進行熱傳效益驗證，以確立雙層熱沉之散熱優勢。
研究結果顯示，均勻入口速度場可藉由極薄之速度邊界層與強烈二次流，有效減緩熱邊界層發展，進而縮減固液界面溫差並維持低對流熱阻，顯著提升局部平均紐塞數與溫度均勻度。在熱浮力效應方面，垂直向上流動組態之近壁區流體因受熱密度降低，誘發之熱浮力可抵消部分壁面黏滯剪切阻力；在不犧牲散熱表現的前提下，成功削減高達48 % 的壓降損失，綜合效能指標最高達1.317。
此外在毫/微米疊置雙層熱沉結構中，提高上層流道雷諾數可顯著增強上下層間之熱耦合效應，不僅全面提升系統總對流熱傳係數，更能重新分佈流道內熱場，建立強烈的橫向與跨層溫度梯度，進而有效消除下層流道中後段因熱邊界層充分發展所累積之極端高溫峰值。雖然上層高流速不可避免地帶來較高的流體阻力，但此高壓降劣勢可藉由熱浮力誘發之自然對流減阻機制獲得緩解，實質提升系統綜合散熱能力。

This study utilizes numerical simulations to investigate the conjugate convective heat dissipation characteristics of a vertical mini- and micro-channel stacked double-layer heat sink system. The primary objective is to reduce the pumping power of the cooling system by innovatively introducing thermal buoyancy effects to improve the pressure drop across the channels. By utilizing buoyancy to induce assisting flow and regulate boundary layer characteristics, fluid resistance is effectively suppressed while maintaining the high heat dissipation advantage of microchannels. To ensure the numerical model accurately reflects practical applications, a uniform flow condition is applied at the inlet boundary to capture the inlet effects and the development process of the thermal boundary layer.
This study is divided into two parts: The first part comprehensively examines the impacts of the inlet velocity field distribution and thermal buoyancy effects on the heat transfer and pressure drop characteristics within the channels. The second part develops a mathematical model of the mini/micro stacked structure and validates its heat transfer efficiency to establish the thermal dissipation advantages of the double-layer heat sink.
The results indicate that a uniform inlet velocity profile effectively suppresses the development of the thermal boundary layer through the formation of an extremely thin velocity boundary layer and strong secondary flows. Consequently, the temperature difference across the solid-fluid interface is reduced while maintaining a low convective thermal resistance, leading to a significant enhancement in the local average Nusselt number and temperature uniformity. Regarding thermal buoyancy, in the upward flow configuration, the fluid adjacent to the heated wall experiences a density reduction due to heating, and the resulting buoyancy force partially offsets the wall-induced viscous shear resistance. Without compromising the heat transfer performance, the pressure drop penalty is reduced by as much as 48%, while the maximum overall performance factor reaches 1.317.

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