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Title: | 皮秒雷射構織仿魚骨圖形於紅銅圓管表面對池沸騰熱傳之影響 Effect of Biomimetic Fishbone Patterns on Copper Tubes Textured with Picosecond Laser on Pool Boiling Heat Transfer |
Authors: | Yu-Ying Chen 陳昱穎 |
Advisor: | 陳炳煇(Ping-hei Chen) |
Keyword: | 超短脈衝皮秒雷射,超親水,魚骨形雷射表面,表面粗糙度,沸騰熱傳係數,熱通量,壁面過熱度, Ultra-fast picosecond laser,Superhydrophilic,Heat flux,Wall superheat,Boiling heat transfer coefficient,Surface roughness,Laser-textured fishbone surface, |
Publication Year : | 2020 |
Degree: | 碩士 |
Abstract: | 本研究使用脈衝皮秒雷射於紅銅圓管上進行表面改質,構織出均質雷射表面及魚骨形雷射表面,與拋光純銅表面比較於池沸騰中之沸騰熱傳性能。在池沸騰實驗中,以去離子水當作工作流體且實驗主要進行於成核沸騰階段(本實驗最高熱通量約至426 kW/m2)。然而,熱通量、壁面過熱度和沸騰熱傳係數均為本實驗的重要參數。與均質雷射改質表面相較,拋光純銅表面具有較高的沸騰熱傳係數,均質雷射表面雖具有較高的表面粗糙度(拋光純銅的平均表面粗糙度為0.025μm,經由雷射改質後,表面粗糙度提升至0.191μm),其超親水的表面特性卻主導了表面的氣泡動力。為了增進銅圓管的沸騰熱傳係數,雷射表面改質採魚骨圖形,其圖形靈感來自於魚骨,目的是為了減少雷射改質面積及增加雷射於圖形邊界所產生的結構,利用邊界產生較多氣泡的現象,將氣泡限制於圖形上,促使氣泡容易相互聚合且離開加熱表面,並藉由較密集的魚骨圖形進一步提升氣泡離開頻率,到達最高熱通量時,沸騰熱傳係數可達至1.12倍的提升相較於拋光純銅表面。在本實驗中,使用雷射共聚焦顯微鏡量測圓管試塊的表面粗糙度及形貌,另外使用高速攝影機記錄在池沸騰過程中每一個試塊表面的氣泡分布及大小,並透過高速影像分析圓管上下表面溫度差的數據趨勢。 In this study, the effect of laser-textured surfaces on pool boiling heat transfer had been investigated. With the ultra-fast picosecond laser surface modification method, patterns with periodic micro-structure could be easily fabricated on surfaces of horizontal copper tubes. These pool boiling experiments were carried out on the nucleate boiling regime (heat flux up to 426 kW/m2) by using deionized water as a working fluid. Furthermore, the heat flux, wall superheat and boiling heat transfer coefficient were mainly investigated. Compared to the homogeneous laser-textured surface, the polished copper surface had larger heat transfer coefficient. Although the laser-textured surface had higher surface roughness, the superhydrophilic characteristic still dominated the bubble dynamics on the surface. In order to improve boiling heat transfer coefficient, the fishbone patterns were selected to apply on surfaces because more laser-textured edges and less laser-textured area could be achieved. Compared to the polished copper surface, the boiling heat transfer coefficient of the laser-textured dense fishbone surface was enhanced up to a factor of 1.12 higher at the highest evaluated heat flux. In addition, the results and discussion were supported by shape analysis of laser confocal microscope. Simultaneously, analysis of the temperature difference along different cylindrical samples was conducted using bubble dynamics. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/51731 |
DOI: | 10.6342/NTU202002706 |
Fulltext Rights: | 有償授權 |
Appears in Collections: | 機械工程學系 |
Files in This Item:
File | Size | Format | |
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U0001-0908202013100100.pdf Restricted Access | 6.11 MB | Adobe PDF |
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