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標題: | 相變化材料與金屬顯微結構之熱放射性質與日間輻射冷卻研究 Study of Daytime Radiative Cooling of Phase Change Materials and Emissivity Property of Metal Microstructure |
作者: | Yi Shao Liu 劉奕劭 |
指導教授: | 陳學禮(Hsuen Li Chen) |
關鍵字: | 相變化材料,日間輻射冷卻,電子元件散熱,熱放射率,碳鋼,不鏽鋼,雙相鋼,顯微結構, Phase change materials (PCM),Daytime radiative cooling (DRC),Electronic component heat dissipation,Emissivity,Carbon steel,Stainless steel,Dual phase stainless steel,Microstructure, |
出版年 : | 2020 |
學位: | 碩士 |
摘要: | 近年來隨著環境與氣候的變遷,環保相關研究日益受到重視。其中相變化材料在儲能與隔熱應用上非常重要;然而相變化材料的光學性質與輻射冷卻相關應用研究卻很少。此外,金屬材料在各領域都相當重要,過去人們對金屬材料之光學與放射率上的研究與應用頗為稀少,以上兩部分將是本論文的討論重點。 本論文主要分為兩個部分:其一為對相變化材料的光學與熱放射性質作探討,模擬聚乙二醇的最佳厚度並考量其於輻射冷卻應用的可行性。和一般輻射冷卻材料相比,相變化材料的潛熱性質,能夠儲存能量以及緩衝,利用此特性表現於電子元件熱緩衝以及輻射冷卻效率上,能夠同時具有輻射冷卻效率與儲存能量穩定溫度的特色。將1克的聚乙二醇錠塊置於模擬太陽燈源的樹莓派中央處理器上,能夠比無錠塊的系統延緩7分鐘達到熱緩衝的效果;而在日間與夜間輻射冷卻效率戶外實驗中,量測出聚乙二醇錠塊的冷卻效率,分別高達55.1和106.2 瓦特/平方公尺。 此外,本論文針對金屬材料的光學與熱放射性質作研究,主要著重於不鏽鋼材料。先將試片經過研磨拋光後去除表面粗糙度以及殘留應力的影響後,量測其可見光到紅外光波段的光譜反射率,以及紅外光的黑體爐熱放射率量測。在7-13微米波段,304不鏽鋼能有15%的熱放射率,大於其他金屬材料。藉由觀察其顯微結構,從金相以及缺陷的角度去探討304不鏽鋼放射率較高的原因,得知沃斯田鐵相的放射率高於其他鐵相,並從材料導電度經德汝德模型計算出各相的光學常數,模擬單相沃斯田鐵與肥粒鐵的光學常數與放射率並與混合雙相作比較,雙相鋼放射率會介於兩者之間並較近於肥粒鐵相;相同化學成分組成的不鏽鋼試片,在表面為光學平坦的粗糙度之下,能夠藉由平均粒徑大小推測其相對放射率大小,平均粒度較大者會有較小的放射率值;在微區傅立葉紅外光譜儀分析中,從試片的多點量測反射率光譜標準差,推測試片相對的缺陷數量,標準差越大者,會有較多的相數或缺陷。此外,也實際探討提升金屬表面放射率的方法。 In recent years, with changes of environment and climate, people start to value the importance of eco-friendly life. Research and studies for environment or energy issues have greatly increased. The techniques related to phase change materials in energy storage and thermal insulation are mature; however, people don’t consider the optical properties in heat dissipation applications of phase change materials adequately. Furthermore, metal has play an important role in the human daily life. However, the thermal emissivity properties of metal have not been discussed deeply. There are two parts in this study. The first part is the investigation of optical and thermal radiation properties of phase change materials. What’s more, simulating the optimal thickness of polyethylene glycol and the feasibility of its application in radiative cooling. In comparison to general daytime radiative cooling materials, phase change materials can store energy and buffer thermal shock using latent heat. By utilizing this special property of phase change materials on heat dissipation and radiative cooling efficiency of electronic components, we can simultaneously achieve efficient radiative cooling and energy storage. Putting one gram of polyethylene glycol ingots on the raspberry pi CPU under the illumination of light source can delay the heat equilibrium temperature by seven minutes compared to a bare CPU body without ingots. In the outdoor experiment of measuring radiative cooling power, the cooling power of polyethylene glycol ingot during day and night times are 55.1 and 106.2 watts/square meter, respectively. The second part of this thesis focuses on the optical and thermal emission properties of metal materials, mainly on stainless steel materials. Metal samples are ground and polished to remove the influence of surface roughness and residual stress. Spectrum reflectance from visible light to infrared light and the thermal emissivity are measured by blackbody furnace. In the spectral regime of 7-13 m, the emissivity of 304 stainless steel emissivity is ca. 15%, which is greater than other metal materials. By observing the microstructures of metal, we can conclude that phase and defect are the factors for higher emissivity of 304 stainless steel. We found that the emissivity of the iron austenitic phase is higher than other iron phases (ferrite and delta). By considering the electric conductivity into the Drude model, we can calculate the optical constants and emissivity of single-phase austenitic iron and ferrous iron. After that, while comparing the optical constants and emissivity of single-phase austenitic iron with the mixed dual phase by Finite-Difference Time-Domain (FDTD), we realize that the emissivity of dual phase metal would be between those of two phases and closer to that of the ferrite. With the same chemical composition and under optically flat surface condition, the relative emissivity of stainless steel samples can be inferred from the mean grain size. The larger the average grain size, the smaller the emissivity value. By using micro-area Fourier-transform infrared spectroscopy (FTIR), the relative defect numbers of the samples can be estimated through the standard deviation of the reflectance spectrum, which were measured from multiple points of the samples. The larger the standard deviation of reflectance, the more phase or defect there is. Furthermore, methods to achieve higher emissivity of metals are also discussed in the thesis. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/72938 |
DOI: | 10.6342/NTU202004481 |
全文授權: | 有償授權 |
顯示於系所單位: | 材料科學與工程學系 |
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