Fabrication And Testing Of Micro Flat Heat Pipes For Light-emitting Diode Modules

LED lighting technology is also known as the" fourth-generation lighting technology", and it is known as energy-saving, environmental, long-life and small size, which is widely used in lighting, backlight, signal indication, decoration and screen display and other fields, having broad prospects for development. A lot of countries which are powerful in science and technology take a research in LED technology and start a drastic technology race. Chinese national planning has list LED lighting technology into Twelfth Five Year Plan and Mid-to-Long Term Plan. There is70%input power of LED chip transformed into heat, so, it will increase the temperature and destroy the LED chip. Therefore, we need to design a simple and efficient cooling method to promote the development of the LED technology. Heat pipe is an efficient passive thermal conduction component based on the mechanism of phase change heat transfer, so it has higher thermal conductivity compared with the normal thermal conduction material. Micro flat heat pipe is a new heat pipe, it was created under the technology development of integrated circuit, and it can decrease the high temperature which will shorten the useful life of LED.In this paper, we design the micro flat heat pipe according to the10W LED module. Backflow of the working fluid is caused by capillary force which produced by micro grooves. The grooves were fabricated on the silicon wafer and followed by bonding with Pyrex7740glass. The working media steam flow across the vapor chamber fabricated on Pyrex7740glass. Deionized water was selected as the working liquid and we designed a charging and sealing system to complete micro flat heat pipes.The equivalent thermal conductivity coefficient was selected as the standard to estimate micro flat heat pipes. According to the formula, we need to measure the input power and the temperature of evaporation and condensation sections. We designed and established the testing system. In order to reduce experimental error, we put the testing part in low vacuum environment. Heat flux sensor and thermocouples which were calibrated were used to test the input power and the temperature inspectively.Formulated the experimental procedures, and tested micro flat heat pipes using testing system. Temperature curves were drawn by dealing with experimental data and the equivalent thermal conductivity coefficient was calculated. A same size silicon wafer was selected as contrast experiment. According the data and the picture, we analyzed the effect of shape of grooves, length of grooves and depth of vapor chamber on thermal conductivity. The experiments revealed the heat transfer characteristics of the micro flat heat pipes in LEDs, and the maximum equivalent thermal conductivity of the MHPs was10.7times that of the silicon wafer.