Investigation of Thin Film Evaporation in Close Loop Thermosyphon

隨著電子工業的發展，電子產品不斷朝著高性能、小體積的方向發展，造成單位面積的發熱量卻是越來越高，產生散熱方面的問題，使得各種電子設備散熱系統因應而生。近幾年來，利用工作流體沸騰與冷凝之相變化以快速帶走熱量的方式被廣泛的應用在解決散熱問題上，迴路式熱虹吸系統即為其中之一。從相關文獻得知，迴路式熱虹吸系統的蒸發器在使用燒結表面及低充填率時會以熱傳性能極佳的薄膜蒸發機制散熱，並指出利用薄膜蒸發機制可設計出散熱效率極佳的蒸發器。 本研究針對迴路式熱虹吸系統設計一套完整的實驗方法，研究加熱功率、充填率、燒結板傾斜角度及燒結厚度對蒸發器熱傳性能的影響。實驗結果發現，蒸發器於不同操作條件下存在四種熱傳型態：(a)燒乾區、(b)薄膜蒸發區、(c)過渡區及(d)沸騰區，經由可視化實驗及理論推導進而得到完整的熱傳型態圖，並證實薄膜蒸發機制有優於沸騰機制的熱傳性能。比較不同熱傳型態圖得知，非水平型式擺設的燒結板擁有較水平型式更大的薄膜蒸發區域，此外，當燒結厚度增加時也明顯有助於擴大熱傳型態圖的薄膜蒸發區域，增進薄膜蒸發機制在實際應用時的使用彈性。With the growth of electronics manufacturing, electronic components become more powerful and the size of them tends to be smaller. It induces the challenge in thermal solution, and several kinds of electronic cooling methods are applied to conquer the thermal dissipation problem. In recent years, the applications of boiling-condensation heat transfer mechanism are widely used for the heat dissipation problem, and closed loop thermosyphon is one of them. It is found in a previous study that thin film evaporation, which has a great heat transfer capacity, occurs in the evaporator of closed loop thermosyphon system while a low fill ratio of working fluid and a sintered evaporation surface are adopted. The presented study focuses on the occuring mechanicsm of thin film evaporation with sintered surface for evaporator design. This paper establishes a set of experimental methods for investigation and analysis of the loop thermosyphon system. The influences of heating power, fill ratio, tilt angle of sintered surface, and thickness of sintered structure to heat transfer performance of evaporator are under concern. The results show that the evaporator has four heat transfer patterns in different operating condition: (a)dry out, (b)thin film evaporation, (c)transition and (d)boiling. It is apparent that the heat transfer performance of thin film evaporation is better than boiling. By comparing different flow patterns, it shows that the sintered surface of non-horizontal type has larger thin film evaporation region than horizontal type and that thicker sintered structure is helpful to enlarge thin film evaporation region.摘 要 I Abstract II 目 錄 III 圖目錄 V 表目錄 VIII 符號說明 IX 第一章 緒論 1 1-1前言 1 1-2文獻回顧 3 1-3研究動機與目的 9 第二章 基本理論 10 2-1熱管原理 10 2-1.1熱管 10 2-1.2兩相熱虹吸管 13 2-1.3兩相迴路式熱虹吸管 14 2-2蒸發基本理論 15 2-2.1彎月形薄膜區之相變化現象 15 2-2.2蒸發增強表面 16 2-3多孔性介質壓差理論分析 18 2-3.1毛細極限 18 2-3.2本實驗毛細性能分析 22 第三章 研究方法 26 3-1實驗方法 26 3-1.1實驗系統 26 3-1.2工作原理 27 3-1.3實驗設備 27 3-1.4實驗參數 29 3-1.5實驗流程 30 3-2分析模式 32 3-2.1熱阻模型 32 3-2.2介面熱阻 33 3-2.3蒸發熱阻 34 3-2.4冷凝熱阻 35 3-2.5對流熱阻 36 3-3誤差分析 37 第四章 結果與討論 39 4-1可視化實驗結果與討論 39 4-1.1蒸氣腔體內水位變化 39 4-1.2四種熱傳型態 41 4-2熱傳型態圖(Flow Pattern)建立與討論 43 4-2.1垂直型式與傾斜45度角型式之熱傳型態圖建立 43 4-2.2水平型式熱傳型態圖建立 45 4-3熱傳型態圖與實驗值之比較 47 4-3.1垂直型式與傾斜45度角型式實驗值 47 4-3.2水平型式實驗值 48 第五章 結論與建議 50 5-1結論 50 5-2建議 52 參考文獻 5