With the excellent thermal conductivity and the compatibility to micro electromechanical systems technology, silicon is widely used in micro heat pipes (MHPs). Copper shows higher heat transfer capability and capillary traction than silicon. Copper microgrooves were fabricated on the silicon wafer using electroforming technique in this paper. Water contact angle measurements and thermal behavior tests demonstrated that copper-grooved MHPs showed better performance than silicon ones. Under the input power of 5.99 W, the equivalent thermal conductivities of copper-grooved and silicon-grooved MHPs were 228.98 W/K · m and 196.26 W/K · m. This work showed the feasibility of copper grooved silicon based MHPs in heat transfer for high-power light emitting diode (HP LED).
High heat flux is the major reason for the malfunctioning or shortened life of high-power light-emitting diodes (LEDs) or integrated circuit (IC) components. Cooling technical devices have been widely studied in recent years. A heat pipe made of silicon wafer and Pyrex 7740 has been used in the experiments. Silicon-to-Pyrex bonding is used for the visualization of the flow behavior of the working liquid in heat transfer. A thermal behavior testing system for micro heat pipes (MHPs), including a vacuum chamber, heat flux sensors and thermocouples, was designed and established. The experiments revealed the characteristics of the MEMS heat pipe in LEDs heat transfer, and the maximum equivalent thermal conductivity of the MHPs was 10.6 times that of the silicon wafer. Furthermore, the structure of MHP can be optimized based on these experimental results. They can also be the experimental basis for theoretical study of two-phase flow on the micro scale.
The light-emitting diode (LED) is a promising lighting source because of its energy-saving and environment friendly features. High-power LEDs have specific wide applications, such as car headlights and street lamps. However, heat transfer is still a critical issue that limits the usage of LEDs. The flat microheat pipe (FMHP) is a suitable passive heat transfer device for LEDs. Silicon substrate was selected to fabricate LED electrodes and the wick structure of the FMHP, and thus, LEDs' mount base and the FMHP were integrated together and the contact thermal resistance could be reduced. Meanwhile, Pyrex 7740, which could be anodic bonded to the silicon substrate and sustained relatively high temperature and pressure, was used to fabricate its cover plate. In this paper, a new type of FMHP is proposed. The cover plate had circles patterned on it, and the etched structure was shell shaped. The contact angle of it was 81.46°, whereas that of the normal cover was 67.97°, which meant that the new cover was more hydrophobic. Theoretically, the new cover could make working fluid drops fall down to the grooves in a relatively shorter time and speed up heat transfer. The evaporator temperatures of the novel FMHP and that of the normal one were 71.6°C and 79.4°C, respectively. In addition, the new designed FMHP also had better temperature uniformity. The experimental results proved that the patterns on the cover plate of the FMHP could promote the heat transfer capability of the LED module.Index Terms-Flat microheat pipe (FMHP), glass cover plate, light-emitting diode (LED) thermal management.
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