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標題: | 晶格波茲曼法於迴路式熱管毛細結構參數之熱傳分析 Effect of Wick Characteristics on Heat Transfer by Using Lattice Boltzmann Method in a Loop Heat Pipe |
作者: | San-Yu Huang 黃三祐 |
指導教授: | 陳瑤明 |
關鍵字: | 迴路式熱管,晶格波茲曼法,孔洞模擬, loop heat pipe,lattice Boltzmann method,pore size simulation, |
出版年 : | 2011 |
學位: | 碩士 |
摘要: | 迴路式熱管為相變化的被動熱傳裝置,在國防軍事工業上已有許多的應用。在迴路式熱管中,蒸發器及其內部的毛細結構為影響系統性能的關鍵元件。然而,在以往的熱傳模型中,毛細結構參數,包含孔隙度、滲透度、孔徑分佈,須仰賴實驗測量而得,使得毛細參數對於系統熱傳性能的影響無法被廣泛地討論。
本研究的目的在建立一迴路式熱管模擬平台,討論毛細參數對系統熱傳性能的影響,並在系統設計上給予建議。以迴路式熱管各元件的尺寸、工作流體性質、操作環境、毛細結構的材料性質與毛細參數為輸入值,求在一熱負載下的穩態性能。本研究在模擬毛細參數的策略如下:(1)以隨機圓球顆粒堆疊的方式,控制孔隙度與粒徑尺寸模擬毛細結構;(2)利用晶格波茲曼法計算毛細結構內流場,求得滲透度;(3)計算隨機球體之間距離得到孔徑分佈。本研究針對氨為工作流體,金屬鎳為毛細結構之迴路式熱管,以粒徑尺寸、孔隙度控制毛細參數,分別探討迴路式熱管在水平、抗重力操作的熱傳與壓降行為。 經毛細結構參數測量以及熱傳實驗驗證,預測與實驗值之間誤差不超過37%。 預測結果顯示:固定粒徑、提高孔隙度,與固定孔隙度、加大粒徑,皆可提升滲透度與平均孔徑。在水平操作時,有利於毛細結構的工質補充與蒸汽排除,降低毛細結構內的蒸汽壓降與蒸發器熱阻,故性能上有較好表現。然而,在抗重力操作時,較大的粒徑產生的大孔不利於毛細驅動力,但過小的粒徑有礙液態工質補充,均造成熱傳性能的下降。總結而言,本研究所發展的模型可針對不同系統操作條件下,提供毛細結構參數的設計參考。 Loop heat pipes(LHPs) are efficient two-phase heat transport devices and have been applied to thermal management in space application. The evaporator and wick’s structure are important components in a loop pipe. The wick’s properties which include the porosity, the permeability, and the pore size distribution are essential. However, most of the mathematical models were developed without considering the relationship among these properties. The range of application and prediction for LHPs will be therefore restricted. The purpose of this work is to develop a mathematical model and to discuss the relationship between the wick’s properties and heat transfer performance. The modeling strategy is as follows: (1) A flow field is established with random particle packing by controlling porosity and particle size. (2)The permeability is calculated by the Lattice Boltzmann Method for the flow field. (3)The pore size distribution is simulated in the packing medium. The heat transfer performance of the LHPs was discussed with different particle sizes and porosities using ammonia as the working fluid at horizontal and vertical operating conditions. The mean absolute errors of wick’s properties as well as the thermal performance prediction did not exceed 37%. The modeling results showed the permeability and the pore size were increased with a larger particle size and a higher porosity. At horizontal operating condition, the higher permeability and average pore size were beneficial for the supplying of working fluid and vapor exhaust. This reduced the vapor blanket and thermal resistance in the wick structure. However, at vertical operating condition, the bigger pores formed by larger particles was disadvantageous for capillary pumping force; and the smaller particles retarded the supplying of working fluid. Therefore, it caused a reduction of heat transfer performance. In conclusion, the development of this work is proved to be a useful tool for the prediction in LHP heat transfer performance. |
URI: | http://tdr.lib.ntu.edu.tw/jspui/handle/123456789/28852 |
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顯示於系所單位: | 機械工程學系 |
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