Fabrication and capillary performance of a novel composite wick for ultra-thin heat pipes

Abstract

The rapid development of high-performance portable electronics requires ultra-thin heat pipes (UTHPs) with higher heat transfer capacity to meet their heat dissipation needs. Wick structure, the key component of a heat pipe, makes a decisive role in the heat transfer capacity of the heat pipe. However, since the wall thickness of UTHPs is typically < 0.1 mm, it is difficult to machine deep enough grooves on the shell to increase the permeability of the wicks like conventional heat pipes. Therefore, a novel composite wick structure with high permeability for UTHPs is proposed in this study. It is found that the wick with larger pores formed by parallel woven spiral meshes have higher permeability, resulting in more working fluid in the wick, which helps delay the drying out at the evaporation end of heat pipes. To further improve the capillary performance of wicks, the effect of thermal oxidation suitable for mass production on the capillary pumping performance of wicks is systematically studied for the first time. Compared with the single sintered wick, the capillary rise height after oxidation at 400 °C, 500 °C, 600 °C, and 700 °C for 150 min increased by about 32.2%, 19%, 19.5%, and 12.9%, respectively. Considering that the copper oxidation may limit the choice of working fluid for the heat pipe, the wicks are heated to 400 °C for reduction reaction for 1 h (with 95% N2+5% H2 gas). The results show that the capillary rise height of the wicks after oxidation at 400 °C, 500 °C, 600 °C, and 700 °C and reduction treatment is about 110%, 127%, 114%, and 91.4% of that of the single sintered wick, respectively. The experimental results show that the maximum heat load power of the UTVCs with 5 layers #200 mesh, single sintered composite wick and 500 °C oxidation–reduction wick are 16 W, 29 W and 38 W, respectively.