Bending the heat: Innovative ultra-thin flexible loop heat pipes for enhanced mobile device cooling

Abstract

The rapid advancement of 5G technology has significantly accelerated the progression of mobile devices, promoting the evolution of electronic products such as smartphones, tablet computers, and virtual reality (VR) and augmented reality (AR) eyewear towards an increasingly foldable design. However, due to the inherent constraints of spatial and structural characteristics, conventional thermal management solutions are no longer adequate to meet the performance requirements of these foldable devices. Therefore, it is imperative to develop efficient thermal management solutions that are compatible with the cross-hinge structures within chip design. This study proposes and fabricates a novel ultra-thin flexible loop heat pipe (UFLHP) with a thickness of merely 0.7 mm to address the heat transfer challenges posed by cross-hinge designs. By utilizing powder sintering and wire cutting techniques, an innovative approach has been developed for fabricating a metallic powder wick with a thickness of 0.4 mm. During the experiments, ethanol was employed as the working fluid to systematically investigate the effects of thermal loading, tilt angle, and bending angle on the steady-state heat transfer performance of the UFLHP. The experimental results indicate that the maximum heat flux density of the UFLHP reaches 5 W/cm2. Under this heat flux density, the evaporator temperature of the UFLHP attains 72.15 °C, while the thermal resistance is measured at 2.48 K/W, resulting in an effective thermal conductivity of 10,273.27 W/(m·K). The tilt angle has a beneficial effect on the UFLHP’s performance under gravitational influence, while the bending angle adversely affects its performance due to increased flow resistance. This research provides a feasible solution for the heat dissipation challenges in foldable electronic devices.