工學院: 機械工程學研究所指導教授: 陳希立施高德Schmid, GerdGerdSchmid2017-03-132018-06-282017-03-132018-06-282010http://ntur.lib.ntu.edu.tw//handle/246246/278441LED燈具需要高效的散熱系統助於提高壽命及功能. 本文分析，優化和比較兩種散熱系統效能，支持高功率LED路燈和泛光燈. 兩個系統,一個被動一個主動,先以實驗研究，然後通過CFD模擬進行大規模的參數研究改進. 被動系統是通過自然對流冷卻的有直鰭片的矩形散熱器. 主要目的是研究鰭片間底座的長度如何影響熱性能. 總共進行55例實驗的檢查，且數據被用來驗證數值模型. 結果表明，較短的鰭片間底座長度有助於系統散熱。傳熱係數增加了高達62.7%，並降低熱阻達36.7%為0.29K/W. 主動冷卻系統是專門為大功率LED路燈. 它是由離心風扇來驅動的槍枝對流散熱系統. 風扇通過一條內管連接到燈頭以形成一個閉環強制空氣冷卻系統，其中燈柱採用於散熱. 實驗中使用的是全尺寸5m總搞的模型進行調查. 該設計包括兩個不同的熱交換器，其分別模擬和分析. 第一個是燈柱的垂直雙管單流熱交換器. 二維軸對稱CFD模型被用來研究燈柱各種流動條件下的傳熱特性. 第二個是燈頭中的水平逆流散熱片, 其模擬為利用ANSYS ICEPAK. 幾何參數和邊界條件, 如入口位置，鰭片厚度和鰭片密度的效果為了優化冷卻系統的傳熱進行分析. 結果表明，逆流散熱器在中間部分較高的散熱片密度可降低熱阻. 兩個散熱系統採用150W COB LED直接熱比較顯示，被動系統能保持LED溫度70度左右在環境溫度30度. 在相同條件下，主動冷卻系統可進一步降低LED的溫度為8-13∘C. 根據兩個散熱系統的24年經濟比較，在考慮成本和能量損耗下，使用被動系統散熱比較划算.Effcient thermal management is one of the most important design considerations for LED applications. This thesis presents a systematic approach to the analysis, optimization, and comparison of two thermal solutions to support high-power LED street and flood lights. Both systems, one passive and one active design, were first experimentally investigated and then numerically improved by performing large-scale parametric studies. The passive solution consists of an oversized, free-hanging rectangular heat sink with straight fins, cooled by natural convection. The main aim was to study how the inter-fin base length influences the thermal performance. A total of 55 cases were examined experimentally, and the data were used to validate the numerical model. The results show that a shorter inter-fin base length can significantly enhance thermal performance, especially when the fins are along the longer base side. For the present case, the heat transfer coefficient was increased by up to 62.7%, and the thermal resistance was reduced by 36.7% to 0.29 K/W. It was further shown that the inter-fin base length greatly influences the optimal fin spacing. In addition, Nusselt correlations including a dimensionless geometrical parameter for the inter-fin base length, which are valid for a wide range of dimensions, were developed. The active cooling system is especially designed for high-power LED street lights. It is driven by a centrifugal fan placed inside a chamber at the lower part of the lamp post. The fan is connected to the lamp head via an internal pipe to form a closed-loop forced air cooling system, where the lamp post is used for heat dissipation. The experiments were conducted using a full-scale model with an overall height of 5 m. The design includes two different heat exchangers, which were separately modeled and analyzed. The first is a vertical double pipe single-flow heat exchanger integrated into the lamp post. A 2D-axisymmetric CFD simulation with Rayleigh numbers of over 10e10 was used to investigate the heat transfer characteristics of the lamp post for various flow conditions. The second is a horizontal counter-flow heat sink inside the lamp head, which was simulated as a 3D-model using ANSYS Icepak. The effect of geometric parameters and boundary conditions, such as the inlet position, fin thickness, and fin density, were analyzed in order to optimize the thermal performance of the cooling system. It was shown that the counter-flow heat sink with a higher fin density in the middle section can reduce thermal resistance. A direct thermal comparison of both cooling systems using a 150 W COB LED revealed that the passive system can keep the excess temperature of the LED close to 40∘C at an ambient temperature of 30∘C. Under the same conditions, the active cooling system can further lower the LED temperature by 8 to 13∘C. Based on an economical comparison of both cooling systems over a period of 24 years, it was concluded that, in its present configuration, the additional costs and increased complexity of the active system outweigh the performance improvements.106722174 bytesapplication/pdf論文公開時間: 2021/8/31論文使用權限: 同意有償授權(權利金給回饋學校)LED自然對流強制對流ANSYS Icepak散熱器傳熱優化Parallel-plate heat sinklight emitting diode (LED)natural convec- tionforced convectionslender cylinderheat transfer optimization.thesis10.6342/NTU201600714http://ntur.lib.ntu.edu.tw/bitstream/246246/278441/1/ntu-99-D99522042-1.pdf