【作者】 王强；

【导师】 朱恂；

【作者基本信息】 重庆大学 ， 动力工程及工程热物理， 2012， 硕士

【摘要】 大功率白光LED（Light Emitting Diode）由于其比传统光源更高的发光效率以及更长久的寿命，使得LED在灯饰照明市场的应用前景日趋广阔。然而随着集成度和功率密度的增加，散热问题成为影响LED性能的关键因素之一，限制了其进一步发展。面对大功率集成LED高热流密度的散热问题，传统的冷却技术已难满足其散热要求。因此，本文提出一种新型的散热器结构，将重力式热管与特别布置方式的圆形翅片相结合，通过自然对流换热方式进行散热。此外，该散热器结构简单、无毛细芯、易于加工，同时，竖直布置的翅片结构不仅利于自然对流换热，还能显著改善翅片结垢问题，其性能可满足大功率集成LED系统的散热要求。本文针对所提出的散热器结构，设计加工了实验样件，对其换热性能进行了实验研究，讨论了不同工质、加热功率和充液量对散热器换热特性的影响。所取得的研究成果如下：①所设计的翅片式重力热管散热器在加热功率为150W，散热热流密度为37.5W/cm2时，翅片式重力热管散热器的系统热阻在0.14K/W-0.25K/W之间，此时蒸发段受热表面温度低于65℃，冷凝段管壁温度相差不超过3℃。该散热器不仅具有良好的均温性，而且在工况变化时，能在很短的时间内（3分钟）重新达到稳定。②以水作为热管工质时，热管散热器的启动性能良好，启动时间随着加热功率的增大而减小，随着充液量的加大而增加。散热器的热阻也随着加热功率的增大而减小，随充液量的增加而增大。由于蒸发段出口的T型结构，散热器在工作时有一定的温度波动，但温度波动幅度在5℃以内。实验工况内，散热器的系统热阻为0.08K/W~0.33K/W，综合换热系数为3200W/(m~2·K)~5700W/(m~2·K)。③乙醇作为热管工质时，当充液量为30%时，实验工况内的启动性能良好。但在20%充液量下，加热功率为200W时散热器蒸发段底部壁面温度升至100.5℃，散热器性能恶化。实验发现，用乙醇作为热管工质时，散热器蒸汽对冷凝液的剪切、携带现象不能忽视，冷凝液受到蒸汽的剪切力停留在绝热段，阻塞了蒸汽的流动通道，导致蒸发腔压力升高。因此，蒸发器壁面温度的迅速升高，影响其对热源的冷却能力。实验工况内，散热器的系统热阻为0.07K/W~0.34K/W，综合换热系数为3500W/(m~2·K)~6000W/(m~2·K)。④在以丙酮作为热管工质时，散热器启动时间迅速，对功率变化响应快。在30%充液量下，加热功率为200W时散热器蒸发段底部壁面温度会在升至95℃以后，突然回落到78℃并保持稳定。散热器的系统热阻随着功率的增加而减小，两种充液量的散热器系统热阻由于绝热段液塞的影响呈现相互交错。在实验工况内，热阻为0.07K/W~0.37K/W，综合换热系数为3000W/(m~2·K)~5700W/(m~2·K)。⑤实验结果表明，工质为水，乙醇和丙酮的最佳充液量都在30%左右。由于实验样件的T型结构，造成水为工质的散热器系统温度具有一定的波动，乙醇和丙酮由于蒸汽对冷凝回流液的剪切、携带作用，会使系统的温度有一次大幅度的振荡，这种振荡带来散热器蒸发段壁面温度飞升，超过了LED的要求温度。更多还原

【Abstract】 Integrated light emitting diode (LED) with large power density has been projectinga brilliant lighting market owing to much higher luminous efficiency than conventionallights. Accompanying with the significant increase in integration and power density,however, the heat dissipation becomes one of the key factors affecting the LEDperformance, limiting its further development. Conventional cooling techniques areunsatisfactory to meet the requirement of the high heat flux cooling inhigh-power-density integrated LED. As a result, towards the heat dissipation problem inhigh-power-density integrated LED, a new type of the fin-type gravity heat pipe radiatorhas been proposed in this thesis. In this design, series of circle-shape fins are verticallyoriented to the outer surface of the heat pipe, by which heat is dissipated by naturalconvection. In addition to the features of the simple structure, no capillary wick andeasy manufacturing, such design not only facilitates the natural convention heat transferbut also effectively solve the fouling problem encountered in the fin type heat radiator.More importantly, the performance of the proposed fin type gravity heat pipe radiator isable to fulfill the heat dissipation demand of high-power-density integrated LED.Following this new design, we designed and fabricated a lab-scale fin type gravity heatpipe radiator and experimentally investigated its heat transfer performance. The effectsof the working fluids, heating power and charge of working fluid on the heat transferperformance were also examined. Main conclusions are presented as follows.①When the heating power was150W and the heat flux was37.5W/cm~2, theoverall thermal resistance of the fin type gravity heat pipe radiator was in arange of0.14K/W-0.25K/W. In the meantime, the surface temperature of theevaporative sector was lower than65℃while the temperature difference inthe surface temperature of the condensing sector was lower than3℃,indicating that the new radiator exhibits good temperature uniformity.Moreover, it is also found that this radiator could reach stable within3minuteswhen the operating conditions vary.②The radiator proposed in this thesis showed a good start-up performance withwater as working fluid. The start-up time decreased with increasing the heatingpower but increased with increasing the charge of working fluid. Under thesteady state, the thermal resistance decreased and increased with increasing the heating power and charge of working fluid, respectively. In this experiment, itis found that due to the T-shape outlet design of the evaporative sector, theworking temperature of the radiator fluctuated but remained in5℃. For givenoperating conditions, the radiator with water as working fluid showed theoverall thermal resistance of0.08K/W~0.33K/W and heat transfer coefficientof3200W/m~2·K~5700W/m~2·K.③When ethanol was chosen as working fluid, the radiator showed good start-upperformance for most given heating power. In the case of20%charge ofworking fluid and200-W power density, the bottom temperature of theevaporative sector increased to100.5℃and the performance of the radiatorbecame worse. In this testing, it is found that when ethanol was used, the effectof ethanol vapor’s shear force and carrying to condensed ethanol wassignificant. As a result of the shear force, the condensed ethanol would stay atthe insulated sector, blocking the ethanol vapor flow and thus leading to theincrease of the pressure in the evaporation chamber. As such, the surfacetemperature of the evaporator was rapidly increased, lowering the coolingperformance. When the charge of working fluid was30%, the start-upperformance of the radiator was favorable. Besides, the overall thermalresistance of0.07K/W~0.34K/W and the overall heat transfer coefficient of3500W/(m~2·K)~6000W/(m~2·K) were achieved under given conditions.④With respect to acetone as working fluid, this radiator showed good start-upperformance under most cases. Rapid start-up and response to the variation inthe heating power were achieved. When the charge of working fluid was30%and the heating power was200W, the bottom temperature of the evaporativesector firstly increased to95℃and then decreased to maintain at78℃. Theoverall thermal resistance decreased with increasing the heating power. It isalso found that the overall thermal resistances of20%and30%charge ofworking fluid crossed each other due to the blockage in the insulating sectors.For given operating conditions, the overall thermal resistances ranged from0.07K/W to0.37K/W and the overall heat transfer coefficients are in therange of3000W/m~2·K~5700W/m~2·K.⑤Experimental results showed that the optimal charge of working fluid for water,ethanol and acetone was all30%. Due to the T-shape outlet of the evaporativesector, the working temperature fluctuated in the case of water as working fluid while the fluctuation became large in the case of ethanol and acetone asworking fluids as a result of the shear force and carrying effect. Such largefluctuation caused a rapid increase in the surface temperature of the radiator,making it unsatisfied for the LED heat dissipation requirement.更多还原