陳瑤明臺灣大學:機械工程學研究所葉建志Yeh, Chien-ChihChien-ChihYeh2010-06-302018-06-282010-06-302018-06-282009U0001-2207200919334900http://ntur.lib.ntu.edu.tw//handle/246246/187251以往迴路式熱管內的單孔徑毛細結構在高熱通量時，內部容易被蒸汽佔據形成蒸氣膜，導致熱傳能力的限制。再者，單孔徑毛細結構的外部溝槽設計一旦決定後，其液態薄膜蒸發的面積便會受到限制。為此，本研究將利用雙孔徑毛細結構來改善上述情況。由於雙孔徑毛細結構的蒸發熱傳，對其內部的液/汽體積比極為敏感，因此本研究將藉由實驗設計與理論分析的方法，探討雙孔徑毛細結構內不同的孔徑分佈對迴路式熱管性能的影響。 在實驗方面，透過改變孔洞成型劑粒徑(32~48μm與74~88μm)、含量(20vol%與25vol%)，與燒結溫度(650℃與750℃)來調控雙孔徑毛細結構內的孔徑分佈，並利用統計方法分析雙孔徑毛細結構的熱傳性能結果，藉此了解各項參數間的影響效應，同時探討雙孔徑毛細結構內不同的孔徑分佈如何影響迴路式熱管的熱傳性能。根據統計分析指出，孔洞成型劑含量的影響與雙孔徑毛細結構的熱傳性能之間有著顯著性的關連，其原因在於雙孔徑毛細結構內由孔洞成型劑所形成的大孔洞擁有自我調節蒸汽通道的數量，隨著孔洞成型劑含量的增加，不但可減少蒸氣膜的形成，更能藉以擴展液態薄膜蒸發的面積。目前在熱沉10℃與容許溫度85℃的實際測試下，實驗結果顯示最佳雙孔徑毛細結構的最高熱傳係數可達68kW/m2.℃，與單孔徑毛細結構相比約可提升5~7倍。另外，就雙孔徑毛細結構應用於迴路式熱管的整體性能而言，其最大熱傳量可達570W (熱通量為29.3W/cm2)且最低總熱阻為0.09℃/W，比起單孔徑毛細結構的熱傳性能400W (熱通量為20.5W/cm2)且總熱阻為0.15℃/W而言，具有相當程度的熱傳提升。 在理論計算方面，發展一同時考慮毛細結構的孔徑分佈與相變化熱傳之改良迴路式熱管的穩態模型，其預測結果與實驗數據比較後，平均絕對誤差百分比(MAPE)約在25%內。透過模型分析指出，雙孔徑毛細結構內不同的孔徑分佈會影響其蒸氣膜的厚度，而蒸氣膜的形成是影響熱傳性能的重要原因之一。另外，模型計算結果亦顯示，雙孔徑毛細結構有利於提供蒸汽的排除，因此受到蒸氣膜的影響程度較單孔徑毛細結構為小，有助於改善迴路式熱管的熱傳性能。 總結而言，雙孔徑毛細結構不僅能有效地增強熱傳能力，更能有利於簡化與取代毛細結構外部溝槽的製造技術。對於未來高功率元件的冷卻而言，雙孔徑毛細結構的技術將是一有效率和簡單的方法。At high heat fluxes, formerly a monoporous wick in a loop heat pipe (LHP) was easily occupied by the vapor to form a vapor blanket, leading to limit the heat transfer capacity. Besides, the surface area for liquid film evaporation was limited after determining the design of outer vapor grooves on a monoporous wick. For these reasons, biporous wicks are utilized to improve the foregoing problems. Because the evaporative heat transfer of a biporous wick is exceedingly sensitive to the internal volume fractions of liquid and vapor phases, the purpose of this study is to investigate the effects of various pore size distributions of the biporous wicks for a LHP by the experimental design and theoretical analysis. xperiments were performed to control the pore size distributions of the biporous wicks by changing the particle size of pore former (32~48μm and 74~88μm), the pore former content (20vol% and 25vol%), and the sintering temperature (650℃ and 750℃). Furthermore, a statistical approach was carried out to analyze the evaporative heat transfer of the biporous wicks, so as to understand the effects of the parameters more effectively. At the same time, how various pore size distributions of the biporous wicks influence the heat transfer capacity of a LHP was examined. According to the statistical analysis, the effect of the pore former content was significantly associated with the evaporative heat transfer of a biporous wick. This is because the large pores formed by the pore former in a biporous wick can self-regulate the amount of vapor passages. With the increase of the pore former content, this not only decreased the vapor blanket but also extended the surface area for liquid film evaporation. Experimental results also showed that, at the sink temperature of 10℃ and the allowable evaporator temperature of 85℃, the evaporative heat transfer coefficient of the best biporous wick, which reached a maximum value of 68kW/m2.℃, was approximately 5~7 times higher than that of the monoporous wick. In addition, in terms of the biporous wicks applying to a LHP, the maximum heat transfer capacity of the best biporous wick achieved 570W (the heat flux of 29.3W/cm2) and the minimum total thermal resistance was 0.09℃/W. Comparing to a monoporous wick of 400W (the heat flux of 20.5W/cm2) and 0.15℃/W, the biporous wick had the suitable degree for the promotion of heat transfer.n improved LHP steady-state model was developed; meanwhile, the pore size distribution of a wick structure and the phase-change heat transfer were taken into account. The results showed that the comparison between the predicted results and experimental data were within 25% of the mean absolute percentage error (MAPE). The model analysis indicated that the vapor blanket thickness formed was affected by various pore size distributions of the biporous wicks and was one of important reasons to influence the heat transfer capacity of a LHP. Moreover, the results of the model calculation also showed the biporous wicks, which were advantageous to the vapor easily escape from the wick, were affected less by the vapor blanket than the monoporous wick and would improve the heat transfer capacity of a LHP.o conclude, the biporous wicks cannot only improve the heat transfer capability but also be advantageous to simplify and replace the manufacturing technology of outer vapor grooves on a wick structure. For passive cooling of high-power components, it will be an efficient and simple approach.誌謝 i文摘要 ii文摘要 iv錄 vi目錄 xi目錄 xiv號說明 xv一章 緒論 1-1前言 1-2文獻回顧 7-2.1雙驅散與雙孔徑毛細結構 7-2.2迴路式熱管的穩態模型 10-2.3毛細結構的熱傳模型 12-3研究目的 15二章 迴路式熱管的操作原理與限制 16-1迴路式熱管的操作基本原理 16-2系統的操作限制 18-2.1毛細限制 18-2.2啟動限制 19-2.3液體過冷限制 19-2.4補償室體積限制 20-3迴路式熱管的熱阻分析 21-3.1蒸發器熱阻 21-3.2蒸汽段熱阻 22-3.3冷凝器熱阻 22三章 實驗設備與方法 26-1雙孔徑毛細結構的設計與製作 26-1.1雙孔徑分佈曲線的毛細結構種類 26-1.2實驗材料 27-1.3製造設備 27-1.4製造方法 29-2雙孔徑毛細結構的參數量測 32-2.1孔徑分佈與孔隙度的量測 32-2.2滲透度的量測 36-3迴路式熱管的測試設備與性能評估 36-3.1測試設備 36-3.2性能評估 38-4誤差分析 40-5迴路式熱管的系統參數 41四章 因子設計與規劃 42-1實驗因子的定義與選擇 42-2實驗方法的簡介 43-3模型建構 44-4二水準因子設計 45-4.1效應分析 46-4.2變異數分析 47-5中心點實驗設計 49-6中央合成設計 50-7反應曲面法 51-8實驗設計的步驟 52-9雙孔徑毛細結構的因子選擇與範圍 54-9.1設計因子的選擇 54-9.2設計因子的範圍 54-10雙孔徑毛細結構的實驗設計與規劃 56五章 雙孔徑毛細結構的實驗結果與討論 58-1實驗與統計分析 58-1.1效應估計 58-1.2變異數分析 60-1.3雙孔徑毛細結構熱傳能力的反應曲面分析 62-1.4追蹤性實驗 65-2 雙孔徑毛細結構的參數影響分析 67-2.1孔洞成型劑粒徑的影響 67-2.2孔洞成型劑含量的影響 68-3單孔徑與雙孔徑毛細結構的熱傳分析與探討 69-3.1熱傳行為的比較 69-3.2孔洞結構的比較 74-3.3孔徑分佈的比較 75六章 迴路式熱管的理論建構 77-1能量傳遞分析 77-2流動壓降分析 80-3系統的穩態模型理論 81-3.1穩態模型的假設與輸入參數 81-3.2穩態模型的計算流程 82-3.3工作流體性質 85-3.4單相壓降之計算 85-3.5單相熱傳之計算 86-3.6二相壓降之計算 87-3.7二相熱傳之計算 90-3.8補償室的能量平衡 91-4毛細結構的熱傳模型理論 96-4.1毛細結構內蒸發模式的描述 96-4.2基本假設 98-4.3臨界孔徑與孔徑分佈曲線的關係 99-4.4毛細結構蒸發模型的數學式 101-4.5蒸發器壁面溫度 105-4.6模型的求解流程 107-4.7預測結果的評估指標 109七章 雙孔徑毛細結構的理論結果與討論 110-1理論預測與實驗結果的比較 110-2單孔徑與雙孔徑毛細結構的比較與分析 111-2.1蒸發模式的影響效應 111-2.2蒸氣膜的影響 113-2.3平均臨界孔徑的變化 115-3雙孔徑毛細結構的分析與探討 117-3.1平均臨界孔徑的變化比較 117-3.2蒸氣膜的比較 119-3.3熱傳性能的比較 120八章 結論與建議 121-1結論 121-2建議 125考文獻 126錄 1344546453 bytesapplication/pdfen-US迴路式熱管單孔徑毛細結構雙孔徑毛細結構孔徑分佈蒸氣膜loop heat pipemonoporous wickbiporous wickpore size distributionvapor blanketthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/187251/1/ntu-98-D94522027-1.pdf