알루미늄 맥동 히트 파이프의 표면 개질을 통한 성능 및 내구성 향상 연구

Abstract

As electronic devices become smaller and lighter, the problem of the management of high heat generation is emerging. The importance of cooling devices is increasing, and it is known that a heat pipe spreading heat with two-phase flows can provide the highest thermal performance. Conventional heat pipes have a disadvantage in a requirement of a wick structure. However, the micro pulsating heat pipe (PHP) has a small channel diameter flows can be generated using capillary pressure even without a wick structure. Water can provide high thermal performance due to its high specific heat and latent heat as a working fluid in PHPs. PHPs using water are commonly made of copper and silicon, but aluminum has the advantage of being longer sustainable than copper and more economical than silicon wafers. In addition, it is possible to reduce weight and improve durability with aluminum. However, aluminum has not been employed as a material for PHPs with water as a working fluid because non-condensable hydrogen gas is generated by the reaction of aluminum and water at high temperature. The non-condensable hydrogen gas leads to the stoppage of flows inside the PHPs resulting in the worst thermal performance. In this study, the surface of aluminum was modified using a micro-nano surface treatment for improving the durability of PHPs. This treatment prevented hydrogen gas formation even at high temperatures by forming aluminum hydroxide which removed the possible reaction sites on surfaces. The wettability of the aluminum channel was modified to superhydrophilic to resolve the performance and durability using water as a working fluid. Water was filled approximately 55% of the channel total volume to make a stable operation and improve durability. The evaporation region was heated through a cartridge heater, and the condensation region was cooled through a Peltier and water block. The thermal resistance was calculated from the measured temperature data at the evaporation and condensation regions with K-type thermocouples for comparing the thermal performance. The durability was evaluated by the reduction of the thermal performances before and after PHP operations. In addition, the flows inside PHPs were visualized to confirm the surface modification effect on the preventing flow motions. The flows inside PHPs were also visualized to compare flow motions before and after the surface modification. Compared to the original PHP, the thermal resistance in the surface-modified PHP is lower due to more water evaporation. The durability was evaluated by the reduction of the thermal performances before and after PHP operations. In original surface PHP, the thermal resistance was increased and dry-out occurred under lower heat conditions as PHP operated. In contrast, in the modified surface PHP (MS PHP), both thermal resistance and dry-out heat condition were kept even after repeated operations. Therefore, the proposed method improved not only the performance but also the durability of water-Al PHPs.