Experimental Study On Cooling Of High-power LED Based On Plate Pulsating Heat Pipe

LED (Light-Emitting Diode), as a new-generation green light source, takes the advantages of high efficiency, longer lifespan, energy-saving and environment friendly in comparing to the traditional ones. So, LED is widely used in various fields. However, high junction temperature of LED chip is detrimental to the performance of it. Hence, heat emitting is an important issue that greatly hinder the development of LED. The present study has conducted a series experiments on cooling of the LED (with rated power of100W) based on an experimental section of the combination of plate pulsating heat pipe(plate PHP) and fins. Two cooling methods are adopted in this paper, which are forced convection and natural convection.Firstly, the forced convection experiments of plate PHP with various heating power and working fluids are carried out. The temperature of evaporation section and the thermal resistance of the plate PHP are both analyzed. The results show that better cooling effect can be obtained when the forced convection is utilized under all the tested operating LED power and the temperatures of evaporation section are far lower than120℃. The study also finds that there is a start-up threshold for the plate PHP, i.e. the plate PHP will start-up only when the power of LED exceeds the threshold. Further more, the temperatures of evaporation section are found to be proportional to the LED power but inversely for the plate PHP thermal resistance. Meanwhile, in the experiments that carried out with three different working fluids of acetone, ethanol and water, the acetone shows best cooling effect.In addition, this investigation puts more emphasis on the experiments of natural convection cooling of plate PHP to study the effect of heating power, working fluids, filling rate, configuration parameter and fins area on the start-up and thermal characteristics of plate PHP. The study shows that, the plate PHP achieve good cooling effect from the natural convection method, only when the power of LED is lower than52W. The thermal characteristics of plate PHP with natural convection cooling possess large disparity compared to that of forced convection cooling. The optimization filling rate is in the range of30%to50%and the thermal performance of plate PHP is better when acetone is used as working fluid than ethanol is. Moreover, the plate PHP with triangle cross section for the channel leads to a lower thermal resistance than that with square cross section. Meanwhile, two hydraulic diameters of channel, i.e.1mm and 0.58mm are introduced and the experimental results show that plate PHP with the former one exhibits better performance. Additionally, the substrate temperature of LED decreases as the fins area increases. According to the analysis of the temperature field of the evaporation section during operating of the plate PHP, it is found that the temperature is almost uniform in this section, in which the deviation is within2.5℃.