An Experimental Investigation on Thermal Performance of Ultra-Thin Heat Pipes with Superhydrophilic Copper Braids

Abstract

This study investigated the thermal performance of ultra-thin heat pipes (UTHPs). The total thickness of the heat pipe was 1 mm and the novel wick structure was copper braids modified to be superhydrophilic with higher capillary ability. This paper is divided into three parts, each focusing on the effect on the heat transfer performance of UTHPs, including the wettability of the wick, the filling ratio (FR), and the variation of sectional lengths. The experimental results indicate that the superhydrophilic wick structure improves the thermal performance of UTHPs, and that the FR of 16.4% results in the best thermal performance of UTHPs. Furthermore, the sectional lengths affect both the thermal resistance and the maximum heat transport capacity. The results indicate that the thermal resistance of UTHPs increases for longer adiabatic lengths but slightly decreases for longer condenser and evaporator lengths. However, because the maximum heat transport capacity is influenced by the effective length of the heat pipe, it is degraded when the adiabatic length or the condenser and evaporator length increases. An UTHP of 55-mm effective length with superhydrophilic copper braids yields thermal resistance around 0.3 /W and the best heat transport capacity of 26.3 W.