因脈衝式熱管無需毛細結構，吸引了許多學者在此被動式兩相流散熱增益機制之研究。近年來，平板型脈衝式熱管之特性應用在均溫板上，是一項相當具有競爭力之被動式散熱元件。本文研究利用鋁平板加工閉迴路流道， 矩形流道之截面積為 1.5mmx2mm， 水力直徑為1.714mm，覆蓋上透明壓克力板，以建立可視化模組， 工作流體為純水。利用高速攝影機，觀測在不同熱負載下，兩相流運動型態對蒸發端溫度之影響，及其有效熱傳之方式，實際觀察到兩相流開始穩定循環流動時，將有最佳熱傳性能。另外製作相同流道之紅銅平板型閉迴路脈衝式熱管，平板尺寸為112mmx48mmx4mm，工作流體為純水，實際量測熱傳性能，在最佳填充率50%及操作角度90°時，可得系統總熱阻為0.52(°C/W)，最大熱傳量為100W。此平板型脈衝式熱管之操作角度極限為20°，當操作角度低於20°時，兩相流無法順利產生振盪以達有效熱傳，因此熱傳接近金屬之熱傳導。最後，本文由可視化模組之經驗，提出平板型脈衝式熱管未來可行之改善方式。

Due to the lack of wick structures, Pulsating Heat Pipes (PHPs) have drawn the attention of many researchers for enhancing heat transfer through passive two-phase flow heat transfer mechanisms. The characteristics of flat-plate closed-loop pulsating heat pipes are recently applied on spreaders and are viewed as competitive passive heat transfer devices. In the present study, flat-plate PHP structures (rectangular cross-section area are 1.5mmx2mm, hydraulic diameter =1.714mm), which are directly machined onto an aluminum substrate (110mmx44mmx3mm) and are covered by an acrylic plate, are made for visualization study. The working fluid is DI water. By using a high-speed video camera, the effects of two-phase flow patterns on the evaporator temperature and the heat transfer mechanism for varied heat load are investigated. The optimal performance of heat transfer occurs when a steadily circulating flow pattern appears. To further examine the thermal performance, a flat-plate PHP made of copper(112mmx48mmx4mm) with the same groove dimensions as that for visualization study is made for the problem of interest. It is found that, with a filling ratio of 50% and a tilting angle of 90°, the optimal performance yields an overall thermal resistance of 0.52(°C/W) and a maximum heat capacity of 100W. The operation limit of the tilting angle is 20° below which oscillating two-phase flows disappear and the heat transfer mechanism approximately becomes a process of pure conduction. Finally, this thesis proposes some workable ways to improve the visualization study of flat-plate PHPs in the future.

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