磁性奈米流體與表面微結構對核沸騰熱傳之影響

Abstract

隨著高效能電子設備的發展，其產生的熱量急劇上升，傳統散熱技術逐漸無法有效應對。兩相浸沒式冷卻技術因其優異的熱傳效能成為未來潛力散熱方案，其中核沸騰區間被視為最有效的熱傳方式。本研究旨在探討表面微結構與磁性奈米流體對核沸騰熱傳的影響，分為三部分進行：修正孔徑對核沸騰起始點(Onset of Nucleate Boiling, ONB)的過熱度影響的預測模型、參考預測模型並以雷射表面紋理化（Laser Surface Texturing, LST）最佳化微孔隙結構，最後探討三種磁場下對不同濃度Fe3O4磁性奈米流體沸騰熱傳影響。 由實驗結果顯示，透過修正汽泡成核標準與探討原始假設，大致符合Hsu所提出的預測孔徑對ONB影響的模型。雷射表面紋理化之微孔隙結構，相較平滑表面，三種表面ONB過熱度均提前，熱傳遞係數(Heat Transfer Coefficient, HTC)亦提升，微孔隙結構平均ONB過熱度提前5.6-5.9℃；在熱通量為500 kW/m2下，平均熱傳遞係數提升140-340%。 透過三種濃度Fe3O4磁性奈米流體應用於池沸騰實驗，並加入無磁場、N-S與N-N三種磁場條件。在熱通量為500 kW/m2時，相較於去離子水，平均熱傳遞係數提升18-45%。

With the advancement of high-performance electronic devices, the amount of heat generated has increased rapidly, making traditional cooling technologies increasingly insufficient. Two-phase immersion cooling has emerged as a promising solution due to its excellent heat transfer performance, especially in the nucleate boiling regime, which is considered the most effective mode of heat transfer. This study investigates the effects of surface microstructures and magnetic nanofluids on nucleate boiling heat transfer, divided into three parts: modifying the predictive model for the effect of cavity size on the superheat of the onset of nucleate boiling (ONB), optimizing microporous structures using laser surface texturing (LST) based on the model, and evaluating the boiling heat transfer performance of Fe3O4 magnetic nanofluids under three magnetic field conditions. Experimental results show that the modified prediction model, which revises the bubble nucleation criteria and examines the initial assumptions, generally agrees with Hsu’s model on the relationship between cavity size and ONB. The microporous surfaces fabricated by LST demonstrated earlier ONB and improved heat transfer coefficient (HTC) compared to smooth surfaces. On average, the ONB superheat was reduced by 5.6–5.9°C, and the HTC was enhanced by 140–340% at a heat flux of 500 kW/m2. Fe3O4 magnetic nanofluids with three volume concentrations were tested in pool boiling experiments under three magnetic field conditions: no magnetic field, N–S, and N–N configurations. At a heat flux of 500 kW/m2, the average HTC increased by 18–45% compared to deionized water.