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LED 다운라이트용 원형 히트 싱크의 최적설계

Title
LED 다운라이트용 원형 히트 싱크의 최적설계
Other Titles
Optimum design of a radial heat sink on a circular disk with application to LED downlight
Author
유승환
Alternative Author(s)
Yu, Seung-HWan
Advisor(s)
이관수
Issue Date
2011-08
Publisher
한양대학교
Degree
Doctor
Abstract
본 연구에서는 LED 다운라이트(downlight)용 원형 히트 싱크의 최적 설계를 수행하였다. 실험을 통하여 수치해석 모델을 검증하고, 원형 히트 싱크 주위의 열유동을 해석하였다. 원형 히트싱크의 열전달 계수를 예측할 수 있는 상관식을 제안하였으며, GUI 환경의 해석 프로그램을 개발하였다. 다양한 형상에 대한 열전달 성능 분석을 통하여 최적 모델을 선정하였고, 열전달 성능뿐만 아니라 방열 성능까지 우수한 히트 싱크에 대한 최적 설계를 하였다. 수치해석 모델의 검증을 하기 위해 총 3개 형상에 대해 자연대류 열전달 실험을 수행하였다. LM 모델과 핀-휜(pin-fin) 모델은 다양한 표면처리를 하여 복사열전달까지 동시에 고려하였다. 수치해석 결과와 실험 결과를 비교하였고, 평균 오차는 2% 이내로 나타났다. 히트 싱크 주위의 유동 형태는 냉각 공기가 히트 싱크 바깥쪽에서 들어와 안쪽에서 상승하는 굴뚝형태이다. 자연대류 열전달만 고려하여 휜의 개수, 길이, 높이와 열유속을 인자로 선택하고, 히트 싱크의 열저항과 평균 열전달 계수의 변화를 살펴보았다. 형상 인자와 발열량으로 히트 싱크의 평균 열전달 계수를 예측할 수 있는 상관식을 제안하였고, 원형 히트싱크의 해석 프로그램을 개발하였다. 최적화 모델을 결정하기 위해 L, LM과 LMS 모델의 열전달 성능을 분석하였으며 그 결과 LM모델이 가장 우수하였다. 방사율 변화에 따른 복사 열전달의 크기를 살펴보았고, 전체 열전달량 중 복사 열전달은 최대 27%를 차지하였다. 방사율에 따라 휜 개수, 긴 휜 길이와 중간 휜 길이가 히트 싱크의 평균 열저항에 미치는 영향을 분석하였다. 인자 변화에 따른 전체 열전달량 중에 복사 열전달이 차지하는 비율의 변화는 미비하였으며, 자연대류 열전달이 전체 열저항에 미치는 영향이 지배적이다. 실험계획법을 통하여 원형 히트 싱크(LM 모델)에 대한 최적 설계를 수행하였다. 방열 성능만 고려하였을 경우에는 최적 모델은 기존 모델에 비하여 평균 12.3% 열전달 성능이 향상되었지만, 질량은 20% 증가하였다. 또한, 최적 모델의 질량을 기준 모델과 동일하게 하여 얻은 최적 모델은 평균 8.7%의 열전달 성능이 향상되었다. 그러나 LM 모델은 히트 싱크 중심부에서 국소 열전달 계수가 낮기 때문에, 다른 휜 형상으로서 핀-휜을 고려하였다. 핀-휜 모델의 히트 싱크를 최적화 한 결과, 열전달 성능은 LM모델과 동일하면서 질량은 20% 이상 감량할 수 있었다.|We investigated natural convection heat transfer around a radial heat sink adapted for dissipating heat on a circular LED (light emitting diode) downlight and optimized heat sink. The numerical results were validated with experimental results. Thermo-flow around a radial heat sink was numerically analyzed. A correlation for predicting Nusselt number of radial heat sink was provided and simulation program was developed. To select the optimum reference model, various heat sinks were compared. Multi-objective optimizations considering thermal performance and mass simultaneously were performed. Experiments were performed to validate the numerical results. Six aluminum heat sinks with different emissivities and shapes were compared and close agreements between experimental and numerical results were found. Thus, it was confirmed that the numerical model can accurately simulate natural and radiation heat transfer around a radial heat sink. Only natural convection around L type radial heat sink was numerically observed. The general flow pattern is that of a chimney
i.e., cooler air entering from outside is heated as it passes between the fins, and then rises from the inner region of the heat sink. Parametric studies were performed to compare the effects of three geometric parameters (fin length, fin height, and number of fins) and a single operating parameter (heat flux) on the thermal resistance and the average heat transfer coefficient for the heat sink array. In addition, a correlation was proposed to predict the average Nusselt number for a radial heat sink. To choose the optimum reference model, we compared the L model (long fin), the LM model (long and middle fins) and the LMS model (long, middle and short fins) and the LM model was found to provide the best heat transfer performance. The effect of radiation on total heat transfer was examined by varying emissivity, and it was found that the maximum radiation contribution was 27%. Parametric studies were conducted to determine the effect of the number of fins, long fin length, and middle fin length on the average thermal resistance of the heat sink. The effect of radiation was smaller than the effect of natural convection over the range of parameters used. The radial heat sink was optimized to maximize thermal performance. The thermal performance was enhanced by 12.3% while the mass increased by 20%. The average thermal resistance of the optimized model with the same mass as the reference model decreased by 8.7%. In addition, pin-fin model was considered and the mass of optimized pin-fin heat sink with the same thermal performance as the LM model was reduced by more than 20%.
We investigated natural convection heat transfer around a radial heat sink adapted for dissipating heat on a circular LED (light emitting diode) downlight and optimized heat sink. The numerical results were validated with experimental results. Thermo-flow around a radial heat sink was numerically analyzed. A correlation for predicting Nusselt number of radial heat sink was provided and simulation program was developed. To select the optimum reference model, various heat sinks were compared. Multi-objective optimizations considering thermal performance and mass simultaneously were performed. Experiments were performed to validate the numerical results. Six aluminum heat sinks with different emissivities and shapes were compared and close agreements between experimental and numerical results were found. Thus, it was confirmed that the numerical model can accurately simulate natural and radiation heat transfer around a radial heat sink. Only natural convection around L type radial heat sink was numerically observed. The general flow pattern is that of a chimney
URI
https://repository.hanyang.ac.kr/handle/20.500.11754/139013http://hanyang.dcollection.net/common/orgView/200000417273
Appears in Collections:
GRADUATE SCHOOL OF ENGINEERING[S](공학대학원) > MECHANICAL & INDUSTRIAL ENGINEERING(기계 및 산업공학과) > Theses(Ph.D.)
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