Thermal performance of ultra-thin flat heat pipes with micro-channel wick

Ultra-thin heat pipes (UTHPs) are the promising solution to the thermal management of highly integrated electronic devices. Due to limited space inside the UTHP, reducing its thickness requires novel wick to provide more space for vapor flow and ensure enough capillary performance. In this paper, an UTHP with thickness of only 0.23 mm is fabricated using novel ultra-thin wick, which features with an array of rectangular cross-sectional micro-channels. With achieving good capillary performance, the wick has only 50 μm in thickness, 28.57 % less than the traditional 300 in⁻¹ mesh wick. The thermal performance of UTHPs is investigated. In horizontal direction, the heat transfer limit of UTHPs with micro-channel wicks is 3 W under the heating size of 2 cm², which increases by 20 % compared with those with mesh wicks. At the gravity-assisted direction, the temperature difference between evaporation section and condensation section can be controlled below 5 °C when the heating power is lower than 2.5 W. The UTHP has higher thermal resistance than that with mesh wick when the heat transfer limit is not reached. This can be attributed to the fact that the proposed wick has low volume-percentage of copper in evaporation section. The optimal ratio of vapor space to wick space is 2, which achieves the maximum heat transfer limit. To further reduce the thermal resistance, the design of micro-channel wicks is theoretically optimized. Compared to the previously reported UTHP with thickness lower than 0.3 mm, the proposed UTHP with micro-channel wick shows advantage of large reduction in thickness but heat transfer limit.