Research On Charging And Testing Of Micro Heat Pipes For High-power LED Modules

Due to their high luminous efficiency, energy saving, environmental protection and many other advantages, LED, which has a very broad application prospect, is called the fourth generation light source. Since the white LED technology has made great breakthroughs, the LED lighting gradually goes into thousands of households, and its market share is increasing year by year. But more and more problems appear, and especially the heat dissipation which is the bottleneck of the application greatly restricts the development of high power LED devices. If the heat generated by the LED cannot be sent out in time, the performance of the LED will be greatly affected, such as red shift of spectrum, the lifetime of devices, luminous attenuation and so on. Therefore, how to carry out the effective heat dissipation of the LED becomes the key issue. As a device for transferring heat through the gas-liquid phase change, the micro heat pipe has attracted more and more attention. Compared with the existing solid materials, the micro heat pipe has a larger ability to conduct heat. With the rapid development of the electronic industry, the integrated level is getting higher and higher. Due to the processing technology of silicon becomes more mature, and its thermal conductivity is higher and the diffusion resistance is smaller, the flat micro heat pipe based on silicon can effectively solve the problem of the heat dissipation for integrated electronic components, especially the high power LED chips.In this paper, the charging of micro heat pipe for high power LED was researched first. Based on the physical properties and the chemical properties of several kinds of commonly used working fluid, DI water was finally determined as the working fluid of the micro heat pipe through comparative analysis and comprehensive consideration. According to the influence factors of the micro heat pipe's heat transfer performance and the size requirements, three different charging methods were designed. The charging errors of the three different charging methods were measured and their advantages and disadvantages were analyzed. In order to ensure the charging accuracy of micro heat pipe, we chose suitable charging method according to the structure and size and actual needs of the micro heat pipe. The process of the sealing of the micro heat pipe was also detailed in this paper.Because there is no heat transfer performance test system of commercial micro heat pipe, so according to the working principle and different heat transfer direction of the micro heat pipe, the test structure platform of the micro heat pipe was designed and built. It was able to adapt to micro heat pipes with horizontal or vertical heat transfer direction. And it provided the testing environment for the performance test of micro heat pipes. The heat transfer performance of micro heat pipes affected by different heat sources were analyzed and researched. The calculation error of the evaluation criteria of the micro heat pipes could be reduced. In order to improve the precision of the temperature acquisition system, a metal probe thermocouple is used and corrected.According to the various factors affecting the heat transfer performance of the micro heat pipe, the heat transfer performance of the micro heat pipes was tested. After the experimental data was processed and analyzed, the temperature-power curves and temperature rise curves of the micro heat pipes were obtained. The thermal conductivity and thermal resistance of the micro heat pipes were calculated, and the influences of different channel shapes, different filling ratios, different inclined angles and different heating sources on the thermal performance of the micro heat pipes were analyzed. Finally, through the experimental tests, it was verified that the micro heat pipe with trapezoid channel shape had better heat transfer performance; the best filling rate of the micro heat pipe was about 30%; the micro heat pipes with different inclined angle had different heat transfer performance and 90 degree angle of inclination was more advantageous to the backflow of the working fluid; micro heat pipe with different heating sources will have different power losses, so the choice of heat source should be carefully considered.