Additive manufacturing of functionally-graded copper/aluminum wick structures by hot-pressing for enhanced thermal performance

Abstract

Two-phase passive cooling systems such as heat pipes and vapor chambers (also known as flat heat pipes) are widely used for its reliable high heat flux cooling capacity and its ability to transfer heat over large distances without requiring high thermal gradient. However, manufacturing of these heat pipes and vapor chambers is highly complicated due to the presence of multi-layered wick structures that facilitate heat transfer by capillary action, preventing surface dry-out in case of high heat flux. Currently, copper is widely used a material to manufacture these wick structures because of its high thermal conductivity and thermal diffusivity. These wick structures are manufactured by pressure-less furnace sintering, but overall manufacturing of such wick structures requires multiple days of manufacturing time. Another approach to manufacture these wick structures is to perform laser sintering but there are many challenges faced such as high reflectivity and thermal diffusivity. To resolve this issue, a novel multi-layered functionally-graded copper/aluminum wick structure is developed by hot-press sintering, to reduce the overall manufacturing time and weight of the heat pipe and vapor chambers. There is a high demand for lightweight high heat flux cooling systems for modern electronic systems. A mold was developed to facilitate the manufacturing process where multiple iterations of molds were manufactured using different materials to find the best suitable mold to withstand harsh environment conditions posed by this hot-press manufacturing process. The multi-layered functionally-graded copper/aluminum wick structures were manufactured by optimizing the manufacturing time where the temperature was 200 °C and pressure was 200 psi. The results show that after 2 hours, the multi-layered functionally-graded copper/aluminum wick structure permeability decreases leading to diminished thermal performance.