LED燈具用改良式輻射狀散熱器之散熱性能研究

Abstract

以鰭片為構造的散熱器採用了被動的方式來進行散熱，其廣泛地被運用在電子散熱的領域之中。因為具有構造簡單，安全且成本低廉等好處，與此同時可帶來良好的散熱效果，是其之所以被普及應用的主要因素。儘管如此，隨著操作的電子元件所消耗的功率變得越來越高，尤其是現今高功率LED燈具的普及下，以往的散熱器出現了無法負荷更高散熱需求的問題。因此，在不改變散熱器的大小或質量下，能夠提高散熱器的散熱能力並且能負荷更高功率的散熱方法為一重要的研究工作。本論文是以一改良型的散熱器作為研究的對象。透過使用計算流體力學軟體Fluent以模擬計算的方式來研究此改良型散熱器的散熱能力。同時，也會參考國外研究的實驗結果進行比較驗證，以確保研究的準確性。對於散熱能力的評估是以散熱器整體的熱阻和電子元件的發熱面溫度在三種不同方向的擺設下作爲探討的指標。與此同時，本論文研究的散熱器參數分別是其鰭片的數量、高度、長度和厚度。藉以了解散熱器上鰭片在不同設計下對於其散熱能力所造成的影響和差異。由分析的結果發現，改良式散熱器比起未改良式散熱器在垂直朝上或朝下擺設時功率12瓦以上，發熱面可至少降低近5攝氏度以上，橫放時可得到更好的散熱效果，其降低了至少近25攝氏度以上。此外，透過在鰭片的定性研究，鰭片的數量，厚度和長度等都對鰭片之間的距離造成影響，也間接影響了散熱的效果。此三個參數會存在一個性能最佳的選擇。鰭片的高度則是與發熱面溫度成反比，但是其散熱效果卻反之會隨著高度而逐漸地減小。同時散熱器的質量也會不斷增加，故散熱能力和散熱器質量以高度考量下需要作出抉擇的考量。

A heat sink of finned structure cools the device and dissipates waste heat by a passive way in heat transfer methods. It has been widely used in the electronic cooling industry for many years. Simple structure, safe and low-cost are the important reasons that make heat sink still popular nowadays. Besides, it still can provide a good efficiency with a proper design. Thus, these make heat sink a good choice in the passive cooling industry. However, the applied power rate of many electronics devices are getting higher as higher recently. Especially, solid state lighting with high power rate is starting to replace the traditional lighting. But due to a poor energy conversion efficiency, it may consume a large amount of power and dissipate more waste heat at the same time. In result, an un-improved heat sink won't able to handle such a large amount of waste heat and so it can't meet requirement of cooling high power rated devices. Therefore, searching for an improved heat sink which can provide a higher amount of potential in handling waste heat dissipation is the key point of study. Studying by using the computational simulation method of commercial computational fluid dynamics software Fluent is able to help us analyzing and comparing the thermal performances of improved heat sinks which have many different designs. In order to ensure the correctness of the simulation results, verifications would be done at the same time by comparing the computational conditions to the similar experimental results from foreign studies. The overall thermal resistance of heat sink and average temperature at the surface of heat source under three different inclined orientations(vertical upward, downward and horizontal) were chosen for the purpose of judging the thermal performance of heat sink. Meanwhile, parametric studies were carried out to find out the effects of fins number, fin height, fin length and fin thickness on the thermal performance of heat sink. According to the studied results, it was found that an improved heat sink which operated at twelve watts and above, it could decreased at least five degree Celsius of heat source surface temperature when it was put in either vertically upward or downward position as comparing to the un-improved heat sink. Moreover, improved heat sink in horizontal position could yield a better performance that the others which the temperature difference could reach at least twenty-five degree Celsius and above. Through the study in the parameters, we found that the distance between fins was the key point which affected the overall thermal performance of a improved heat sink. This distance was decided by the numbers of fins, fin length and also fin thickness. While the fin height had an inversely proportional relationship with the thermal resistance and heat source surface temperature. But this phenomenon would become more non-obvious as the fin height was higher than a certain level. Also, the increased mass of heat sink due to fin height might not provide a corresponding acceptable thermal performance at the same time. This implied that there was a consideration to make between choosing either the thermal performance or the heat sink mass at same time.