本研究利用商業套裝軟體CFD-RC，來探討不同鰭片數(N=2、4、6、8)運用於LED汽車頭燈之散熱效益。考量燈具在應用上受到防塵、防水及防震的限制，本燈具的散熱設計採用被動式散熱方式。在考慮自然對流及輻射的狀態下進行模擬，並以實驗的數據來加以驗證。LED輸入功率為10.8W時，將實驗與數值模擬數據比較，其溫度誤差值約為6％，因此可藉由數值模擬來探討LED功率為15W時，不同鰭片數之散熱情形。以相同鰭片作為散熱系統，LED輸入功率分別為10.8W及15W時，接面溫度隨功率增加而遽增。可藉由LED之相關資訊，得知LED的亮度將伴隨著接面溫度升高而導致光衰的現象增加及波長偏移。
由於鰭片表面因溫度梯度而產生自然對流，當鰭片間之間距縮小時，會導致空氣流動速度降低，並影響其LED散熱效益而造成波長偏移及亮度衰退，使得光源所發出的白光無法滿足汽車頭燈法規之要求。從數值分析得知，LED約88％的熱能是藉由散熱鰭片將熱能傳導至外部空氣，欲使LED有良好的散熱效益，需考慮其散熱系統的設計。

In this research, the commercial solver, CFD-ACE+, had been used to study the effects on different number of fins in Light emitting diode (LED). Due to the limitation of waterproof, dustproof and shockproof, the thermal dissipation of this headlamp was considered as passive cooling device. LED headlamp was simulated with four different types of heat fins under the condition of natural convection and radiation, and these simulation results were compared with the experimental data. When the input power was 10.8W, the error between simulation and experiment is only 6%. So it is confirmed that the simulation results can represent experimental data. When input power were 10.8W and 15W, the results shown that the temperature of LED raised as input power increased. According to the LED’s technical datasheet, the optical output of LED accompanied the junction temperature raised then which caused luminous flux reduction and wave length shift.
The temperature gradient on fin surface will bring about natural convection. If the gaps of fins decrease, velocity of the air flow is decreased and results in the decrease of heat dissipation. If the fins can not spread out the heat generates by LED, white light will not meet the regulation requirement of the automotive headlamp and shift in the emission wave length. The numerical investigation shown that heat generated by LED can diffuse from heat fin to air about 88%, so it can make a conclusion that the design of fins has a greatly influence on efficiency of heat diffusion.

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