Development of Loop Heat Pipe Steady-State Model and its Application

迴路式熱管(Loop Heat Pipe, LHP)是一種具備高熱傳量、長傳輸距離的被動二相熱傳裝置，並廣泛應用於航太與電子冷卻領域。數學模型的建立可以幫助對迴路式熱管在設計與性能上的預測，而二相區熱傳與壓降上的分析可使預測結果更加精確。本文將探討迴路式熱管穩態數學模型的建立與應用，數學模型根據迴路式熱管各元件間的穩態能量平衡，並將各區段之單相、二相熱傳與壓降、以及環境間的熱交換皆納入考量，建立補償室穩態溫度與輸入熱量間的關係以及最大熱傳量的預測。預測結果與國外文獻比較後平均絕對誤差為10.2%，二相熱傳與壓降關係式選用上的不同為誤差的主要來源。 經由參數的分析，可依據壓降與穩態溫度上的考量，將影響系統性能參數分為重要參數與次要參數兩部份。重要參數依序如下：(1)毛細結構有效孔徑(2)毛細結構孔隙度 (3)毛細結構厚度等；次要參數則包括選用的工作流體、管材、蒸發器、傳輸段、冷凝段、以及補償室的尺寸等。本研究建立一方法，就熱傳需求（最大熱傳量、補償室穩態溫度）與製作上的考量，利用穩態模型決定主要參數的最佳值，幫助迴路式熱管系統的設計與改良。 實驗方面建立單孔徑毛細結構之有效孔徑與孔隙度、有效孔徑與滲透度兩關係式，並利用穩態模型分析後，找出能使迴路式熱管具較佳性能之毛細結構參數。最後選擇具特定參數之毛細結構進行性能測試，理論與結果值之平均絕對誤差為約為11%，主要是低輸入熱量下的熱洩漏量以及與環境熱交換高於理論預測值所致。因此藉由穩態模型的建立，不僅能作為迴路式熱管在性能預測上的依據，更能在應用方面了解系統內各項參數改變如何影響整體性能的效應，並作為系統設計上的參考。Loop heat pipe (LHP) is a passive two-phase thermal transport device with high heat transfer capacity and long transport distance, and is widely used for aeronautics and electronic cooling. A mathematical model to simulate the thermohydraulic performance of LHPs is required for a design of such a thermal device. This study focuses on the development and application of LHP 1-D steady-state model. Mathematical model is based on the steady-state energy balance equations at each component of the LHP. The heat transfer, pressure drop and heat exchange with ambient between each component are also taken into account. Loop operating temperature is calculated as a function of the heat load, and the maximum heat transfer capacity is also predicted. Predicted result with reference data is within 10.2%. Dissimilarities between two-phase pressure drop correlation and heat transfer correlation are the main sources of error margin. In considering the pressure drop and steady-state temperature, relative parameters are divided into two parts. The primary parameters are as follows: (1)wick effective pore radius;(2)wick porosity;(3)wick thickness. Secondary parameters include the working fluid, the tube material, and the size of evaporator, condenser, transport region, and compensation chamber. In this study we present a methodology to assistant and improve the design of a LHP. According to the requirements for heat dissipation and the consideration for manufacture, the fine primary parameters can be determined by steady-state model. In the aspects of experiment, two correlations between the effective pore radius and the porosity, the effective pore radius and the permeability of the wick, are established and used for the steady-state model calculations for the predictions of better wick parameters. A wick with fine design parameters is chosen and tested for the heat transfer performance. The comparison between the predicted results and experimental data shows a good agreement (within 11%). To summarize, the development of a LHP steady-state model is proved to be a useful tool for the study and prediction in LHP performance characteristics.致謝 中文摘要 英文摘要 目錄 i 圖目錄 iv 表目錄 vi 符號說明 vii 第一章 緒論 1 1.1前言 1 1.2文獻回顧 7 1.3研究目的 11 第二章 迴路式熱管基本原理 13 2.1系統操作原理 13 2.1-1毛細限制 15 2.1-2啟動限制 16 2.1-3液體過冷限制 17 2.1-4補償室體積限制 17 2.2能量流動分析 18 2.2-1系統能量傳遞過程 18 2.3流動壓降分析 21 第三章 穩態能量模型 23 3.1數學模型的假設 23 3.2模型計算流程 24 3.2-1工作流體性質 24 3.2-2單相壓降與熱傳之計算 24 3.2-3二相壓降計算 27 3.2-4二相熱傳計算 30 3.2-5毛細結構壓降 31 3.2-6蒸發器至補償室間之熱傳 33 3.3穩態模型計算流程圖 38 第四章 實驗設備與方法 41 4.1迴路式熱管測試設備 41 4.2毛細結構製造設備 43 4.3毛細結構參數量測 44 4.3-1孔隙度 44 4.3-2有效孔徑 45 4.3.3滲透度 47 4.4實驗步驟 48 4.4-1毛細結構製作與測試步驟 48 4.4-2迴路式熱管熱傳性能測試步驟 49 4.5誤差分析 51 4.6實驗參數 52 第五章 結果與討論 53 5.1穩態模型預測結果 53 5.1-1穩態模型輸入參數 53 5.1-2預測結果與討論 54 5.2穩態模型的應用與參數探討 61 5.2-1次要參數的選定 62 5.2-2毛細結構主要參數探討 66 5.2-3迴路式熱管設計實例 72 5.3毛細結構參數量測與性能測試 73 5.3-1毛細結構參數之量測與應用 73 5.3-2性能測試 77 第六章 結論與建議 81 6.1結論 81 6.2建議 83 參考文獻 84 附錄 8