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A study on parameters for the micro flow of hot melting PCM between the interfaces
Micro heat conduction
Phase Change Material(PCM)
|Issue Date: ||2009-12-29 15:35:20 (UTC+8)|
|Abstract: ||自然界各種能量的轉化使用不但可改善人類的生活品質，亦可改善地球的生存環境。而熱能之存儲對於太陽能應用而言，具有舉足輕重的地位。在各種儲能之技術中，潛熱式儲能技術由於具有提供高能量密度及在PCM(相變化材料)之相轉換的固定溫度點工作之能力，而被公認為最有發展潛力。PCM 可由固體轉換成液體，或由液體轉換成固體，這種現象稱之為材料轉換狀態或是相變化。這些固體-液體的相變化材料不像一般的存貯材料，在吸收熱能的時候溫度會昇高，相變化材料在吸收熱能或釋放熱能的時候，本身處於幾近恆溫的狀態，不會有局部溫度驟昇或劇降的情況產生。PCM 每單位的熱容積存貯量比一般可見的水或岩石存貯的熱容積高出5-14 倍以上。大多數的低成本儲能材料的熔點有其一定範圍。然而，作為潛熱儲熱材料須具備某些條件才能被工業界所使用，亦即必須要能在能源供給和需求之間取得平衡的能力，因此必須探討在溫度變化過程中其熱傳導、熱對流之特性及可能發生的體積變化對於材料熱阻所造成的交互影響。PCM 材料的熱傳實驗較金屬薄膜困難許多，影響實驗的參數也更複雜，需要一系列研究來驗證其物理意義，目前僅就太陽能熱水器應用上的需求進行研究。實驗結果顯示：65℃熔點之PCM 材料於輕負荷下其接觸熱阻隨溫度升高而略為增加，並於接近溶點溫度時出現較大幅變動。當增加荷重後，接觸熱阻隨溫度增高而略為降低。本研究除能分析相變化材料溶化前後的接觸熱阻變化趨勢之外，也能以接觸熱阻的變化而推論其發生相變化之臨界溫度與荷重的關係。
The natural compatible source of renewable energy plays an important role for the human life and the environmentally quality. Thermal energy storage is very important for solar energy applications where solar radiation (variable nature) is the energy input. Amongst various thermal energy storage techniques, latent heat storage is considered to be most promising due to its ability to provide the high energy density and to store the heat at a constant temperature corresponding to the phase transition temperature of the phase change material (PCMs). PCMs are Latent heat storage materials. The thermal energy transfer occurs when a material changes from solid to liquid, or liquid to solid. This is called a change in state, or Phase. Initially, these solid – liquid PCMs perform like conventional storage materials, their temperature rises as they absorb heat. Unlike conventional (sensible) storage materials, PCM absorbs and release heat at a nearly constant temperature. They store 5 to 14 times more heat per unit volume than sensible storage materials such as water, masonry, or rock. A large number of PCMs are known to melt with a heat of fusion in any required range. However, for their employment as latent heat storage materials these materials must exhibit certain desirable conditions. Such as heat conduction, heat convection, the variations of volume. Moreover, the PCM to be used in the design of thermal storage systems should pass the above conditions in advance. The experimental results showed that the thermal contact resistance slight increased with increasing the heating temperature under low normal load. Moreover, it showed larger variations when the heating temperature was near 65℃. With increasing normal loads, the values of thermal contact resistance slightly decreased with increasing the heating temperatures. On the whole, all of the above results indicated that the thermal contact resistance was significantly influenced by the phases of PCM. Therefore, the relationships between the critical temperature of phase change and the normal loads can be clarified by the variations of thermal contact resistance. The results of this project were very helpful in design and research for the industry in the future.
|Appears in Collections:||[機械工程系所] 研究計畫|
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