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Title: | 雷射表面改質與應用Mask R-CNN於沸騰熱傳之影響 Effects of Laser Surface Modification and Application of Mask R-CNN on Boiling Heat Transfer |
Authors: | 周劭穎 Shao-Ying Chou |
Advisor: | 黃振康 Chen-Kang Huang |
Keyword: | 池沸騰,表面改質,雷射紋理化,氧化銅奈米線,Mask R-CNN, Pool Boiling,Surface Modification,Laser Surface Texturing,Cu2O/ CuO nanowires,Mask R-CNN, |
Publication Year : | 2023 |
Degree: | 碩士 |
Abstract: | 近年來,隨著5G、機器學習和區塊鏈等技術快速發展,數據中心在有限的空間下對運算能力的要求越發嚴苛,使得所需之熱設計功耗大幅提升,導致大量的熱無法被有效的散去。因此,引入具有更高對流熱傳係數的兩相浸沒式冷卻技術被視為是一種具有前景的先進散熱策略。
本研究設計了四種雷射表面紋理化 (Laser Surface Texturing, LST) 的路徑分別為線狀、交叉線狀、孔洞I與孔洞II,用於純銅與鋁6061兩種金屬進行表面改質,並將純銅雷射改質進一步做熱氧化 (TO),進行池沸騰實驗。另外,高速攝影機蒐集得到的汽泡影像用以訓練神經網路模型Mask R-NN以進行汽泡分析。 應用LST技術之雷射加工結果顯示,交叉線狀路徑LST技術應用表面改質,若雷射能量充足,會在交點處會形成規則緻密的孔洞。孔洞I及孔洞II路徑則會在接近圓心處因為雷射光斑的重疊而產生深入的孔洞。 池沸騰實驗結果顯示,線狀路徑於純銅的表面改質,核沸騰起始點降低了4.2 ℃,對流熱傳係數為原本之112 %;於鋁6061的表面改質,核沸騰起始點無顯著變化,而對流熱傳係數為原本之149 %。交叉線狀路徑於純銅的表面改質,核沸騰起始點降低了4.3 ℃,對流熱傳係數為原本之161 %;於鋁6061的表面改質,核沸騰起始點降低了6.8 ℃,對流熱傳係數為原本之158 %。孔洞I路徑於純銅的表面改質,核沸騰起始點降低了4.8 ℃,對流熱傳係數為原本之124 %;於鋁6061的表面改質,核沸騰起始點降低了6.0 ℃,對流熱傳係數為原本之111 %。孔洞II路徑於純銅的表面改質,核沸騰起始點降低了3.2 ℃,對流熱傳係數為原本之158 %;於鋁6061的表面改質,核沸騰起始點降低了6.1 ℃,對流熱傳係數為原本之130 %。對四種不同雷射路徑於純銅的表面改質進一步做熱氧化 (TO) 長出奈米線結構進行沸騰實驗後發現,對流熱傳係數相比沒做TO都有所下降,這是由於奈米線的斷裂導致與方向不一致導致汽泡纏結,從而降低對流熱傳係數。另外,Mask R-CNN模型成功讀取汽泡影像並對汽泡個數進行量化。在低熱通量時,可以用來判斷成核點的多寡;當汽泡數大幅下降時,可以用來判斷汽泡劇烈合併時的熱通量。 In recent years, with the rapid development of technologies such as 5G, machine learning, and blockchain, the demand for computational power in data centers has become increasingly stringent within limited space. Therefore, the introduction of two-phase immersion cooling, which offers a higher convective heat transfer coefficient, is regarded as a highly promising advanced thermal management strategy. This study designs four laser surface texturing (LST) patterns, including line-like, crosshatch-like, hole I, and hole II, for surface modification of pure copper and aluminum 6061. Furthermore, the laser-modified pure copper samples are subjected to thermal oxidation (TO) treatment for pool boiling experiments. High-speed camera images of the boiling bubbles are collected and used to train a neural network model, Mask R-NN, for bubble analysis. The results of laser processing using LST technique demonstrate that the crosshatch-like pattern can effectively modify the surface, forming regularly spaced and dense holes at the intersection points when sufficient laser energy is applied. On the other hand, the hole I and hole II patterns result in deeper holes near the center due to the overlapping of laser spots. The results of the pool boiling experiments showed that for the surface modification of pure copper using the line-like pattern, the onset of nucleate boiling point was reduced by 4.2 °C, and the convective heat transfer coefficient increased to 112 % compared to the smooth surface. On the other hand, for the surface modification of aluminum 6061 using the line-like pattern, there was no significant change in the onset of nucleate boiling point, but the convective heat transfer coefficient increased to 149 % compared to the smooth surface. For the surface modification of pure copper using the crosshatch-like pattern, the onset of nucleate boiling point was reduced by 4.3 °C, and the convective heat transfer coefficient increased to 161 % compared to the smooth surface. Similarly, for the surface modification of aluminum 6061 using the crosshatch-like pattern, the onset of nucleate boiling point was reduced by 6.8 °C, and the convective heat transfer coefficient increased to 158 % compared to the smooth surface. For the surface modification of pure copper using the hole I pattern, the onset of nucleate boiling point was reduced by 4.8 °C, and the convective heat transfer coefficient increased to 124 % compared to the smooth surface. Likewise, for the surface modification of aluminum 6061 using the hole I pattern, the onset of nucleate boiling point was reduced by 6.0 °C, and the convective heat transfer coefficient increased to 111 % compared to the smooth surface. For the surface modification of pure copper using the hole II pattern, the onset of nucleate boiling point was reduced by 3.2 °C, and the convective heat transfer coefficient increased to 158 % compared to the smooth surface. Similarly, for the surface modification of aluminum 6061 using the hole II pattern, the onset of nucleate boiling point was reduced by 6.1 °C, and the convective heat transfer coefficient increased to 130 % compared to the smooth surface. Furthermore, after further thermal oxidation (TO) treatment to grow nanowire structures on the surface modifications of the four different laser patterns on pure copper, it was found that the convective heat transfer coefficient decreased compared to the case without TO treatment, which may be due to the inconsistent directions caused by the fracture of the nanowires. Additionally, the Mask R-CNN model successfully read the bubble images and quantified the number of bubbles. It can be used to assess the abundance of nucleation sites at low heat fluxes and to determine the heat flux during intense bubble coalescence when the number of bubbles decreases significantly. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/89037 |
DOI: | 10.6342/NTU202303401 |
Fulltext Rights: | 同意授權(限校園內公開) |
Appears in Collections: | 生物機電工程學系 |
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