Micro Heat Transport Characteristics Of Flat Micro Heat Pipe For Heat Dissipation In High Power LED

LED (light emitting diode) is regarded as a new light source that can take the place of traditional light source in this century. LED is of big strategic significance for the development of low-carbon and resource saving society. China has list LED into the national program of the Twelfth Five-year Plan and the Medium and long-term science and technology plan.80percent of the LED’s power transformed into heat, and with the increase of service power, the heat dissipation increased immediately. If the heat couldn’t dissipate in time, when the temperature exceeded a specific value, LED would fail. Thus, how to improve the heat dissipation capacity is one of the problems that high power LED should solve.Researchers in China and abroad focused their eyes on the MHP (micro heat pipes) now. Compared with the traditional method of heat dissipation, MHPs have special advantages, such as high heat transfer efficiency, good heat transfer performance, smooth out surface and simple structure, et al.. In recent years, MHP has been a main method of high power LED’s heat dissipation problem. MHP used in the heat dissipation of high power LED was studied in this paper, and make analysis research in the theory aspect.First of all, the working principles of MHP was described, including the formation of capacity force and the definition of contact angle, and analyze the heat transport limitation that may be met in the working condition of MHP. Then the heat transfer theory of axial capacity flowing in the grooves of MHPs was analyzed, too. In this process, the control in the form of differential equations and Laplace-Young equation were used to build one-dimensional mathematical model. Differential equations were solved by MatLab software, and the results of capacity force distribution, flowing liquid press and velocity distribution in the axial were arrived. The maximum rate of heat transfer of MHP was predicted and was found to meet with the experimental results.Numerical simulation’s calculation is simple, but the solution precision depends on the equation, and a high dimension model is difficult to establish. On the basis of this method, simulation software method which had higher precision was used to establish a three-dimensional model, so could we have a further research on the thermal performance of MHP. Secondly, build multi-phase model of MHPs and use VOF model of ANSYS FLUENT software to analyze the heat transfer characteristic of MHPs. The quality and energy source term of control equation was increased to simulate the evaporation and condensation of working liquid in MHPs by the UDF function of the software. Then the temperature, the volume rate of working liquid and the flowing velocity distribution of MHPs were arrived to better know the phase change process in MHPs. The simulation results were compared with the experiment results.Finally, this paper focused on the factors that impacted the heat transfer characteristic of MHPs, including the aspect ratios of grooves, length of MHPs, filling ratio and contact angle, et al.. Through the simulated results, the laws how the factors above impacted the heat transfer characteristic of MHPs was analyzed to lay a theoretical foundation for the optimal structure designing of MHPs.