- 學位論文
應用銀、二氧化鈦奈米流體增強脈衝式熱管性能之研究
Thermal Enhancement of Pulsating Heat Pipe by using Ag、TiO2 Nanofluid as working Medium
摘要
閉迴路脈衝式熱管(Closed-Loop Pulsating Heat Pipe, PHP)是一項具有高效能之熱傳裝置，主要是由氣液兩相之作動原理，可將高溫區之熱源有效傳至低溫區。本研究以奈米流體增加熱傳方面進一步研究，以高速攝影機及熱影像分析儀，來探討PHP系統之氣泡型態及全溫度場分布之情形，並改變不同參數，如工作流體、傾斜角、填充比、負荷量對性能提升的影響。 結果顯示：(1)流場流動模式分為震盪期、過度期與穩態期；(2) PHP流場型態分為微小氣泡、彈狀、長彈狀與環狀流。微小氣泡只在震盪期出現，而穩定狀態後，冷凝端出口為彈狀，蒸發端出口為長彈狀與環狀；(3)工作流體性質不同，所觀測到彈狀氣泡形狀也不同，水為子彈狀、銀與二氧化鈦奈米流體分別為橢圓與琵琶狀；(4)本實驗所製作之PHP性能模組，在傾斜角90°與填充比30﹪時，奈米流體最大負荷量所對應之熱阻值均比水佳；(5)奈米流體經由長時間測試，奈米流體的性能趨近於水，不利於長久使用；(6)在穩定期全溫度場分布，為兩相流體沿著固定方向循環，其流場溫度並非呈現沿著循環方向遞增或遞減，而是以不均勻的溫度分布。
並列摘要
Pulsating heat pipe (PHP) is a new heat transfer device, which can transfer the heat from one end to the other end by the mechanism of pulsating action of the liquid-vapor system. The thesis aimed to discover area on the nano-fluid increasing heat transfer further. To discover bubble type of PHP system, changeful temperature condition by observing their actions with high speed, thermal imaging machine. Through analysis of the features, I explore the influence under different parameters of work fluid, fill ratio, angle of inclination and heating load . The experimental results show that: (1) The input heat flux will change the flow pattern inside the PHP tube, which can be divided into three periods-oscillating, transitional and stable periods. (2) PHP fluid field type can be divided into dispersed bubble, confined bubble, slug and annular flows. Dispersed bubble only appears in periods-oscillating. After stability, the condenser exit will be confined bubble and the evaporator exit will be straight confined bubble and annular flows. (3) When the work fluid properties are different, observing the difference of confined bubble. For example, water is confined bubble, silver and titanium dioxide are dividedly elliptic mode and pipa mode. (4) The experience will make a PHP performance model. The PHP heat resistance value will be the lowest when the work fluid of nano-fluid(silver and titanium dioxide) and water under the conditions of FR 30%, angle of inclination 90°. (5) When nano-fluid is testing through the long time, its performances close to water and unuseful in long. (6) It is the two-phases circle along steady direction on spreading temperature field of stable periods. The temperature of fluid would rather be uneven spreading temperature than appear increasing along circular direction.