Session: 11-01: Micro/Miniature Two-Phase Devices/ Systems

Paper Number: 130870

130870 - Experimental Study on Heat Transfer Characterisitics of Flexible Loop Heat Pipes for Mobile Devices 

Abstract: 

    The 5G technology has facilitated the rapid development of virtual reality (VR) and augmented reality (AR) devices, making them lighter, more compact, and high-performance, which are already playing an important role in gaming and entertainment, healthcare, artistic creation, automotive and aerospace, industrial maintenance, and architectural design, thus requiring efficient and hinge-compatible thermal management methods on the chip. The existing high-efficiency thermal management materials, such as vapor chambers or heat pipes made of rigid metal, are inadequate for more than 50000 times repeated bending. As a result, nearly 50% of the surface area of AR/VR glass is wasted, and heat generation is a growing concern, severely limiting its performance. For these reasons, a new ultra-thin (0.6 mm thickness) flexible loop heat pipe (UFLHP) was proposed and prepared in this study to solve the cross-hinge heat transfer problem by replacing the loop heat pipe gas-liquid line with a flexible line. A novel method for preparing the ultra-thin (thickness 0.4 mm) metal powder capillary wick was proposed by using powder sintering and wire cutting techniques. The liquid absorption performance of the ultra-thin capillary wick was thoroughly examined by considering various factors such as particle size, pore-forming agent content, and metal powder material. Theoretical analysis and experimental study of UFLHP were carried out using anhydrous ethanol as working fluid. The effects of filling rate, tilt angle and integrated sintering on the steady-state heat transfer performance were systematically investigated. Constant power startup and variable power startup experiments were also carried out on the UFLHP to verify the stability and reliability of the UFLHP in practice.The results demonstrated that the liquid-absorbing core of 100 μm granular vegetation without pore-forming agent had the best liquid-absorbing and strength properties. In addition, the UFLHP can be started normally with a fill rate of 50% or less. The overall performance of the UFLHP is best at a 30 per cent fill rate. The integration of the wick and baseplate effectively reduced the contact thermal resistance, resulting in an improvement in the heat dissipation performance of UFLHP. Under the natural convection heat dissipation condition of the condenser, keeping the chip below 90°C, the UFLHP achieves a maximum heat dissipation heat flow density of 5W/cm², a minimum thermal resistance of 1.34°C/W, and a maximum equivalent thermal conductivity of 19,013W/(m·K) at a distance of 200mm. In addition, UFLHP has excellent tilt resistance and can operate stably in a range of tilt angles from -90° to +90°, providing a promising new idea and direction for the development of heat dissipation in foldable electronic devices.

Presenting Author: Qingjie Cui Xi'an Jiaotong University

Presenting Author Biography: Qingjie Cui received the B.S. degree in Process Equipment and Control Engineering from the China University of Petroleum, Qingdao, China, in 2022. He is currently working toward the M.S. degree in Materials and Chemicals at Xi'an Jiaotong University, Xi'an, China. His research interests include loop heat pipes, phase-change heat transfer, and electronic devices.

Authors:

Qingjie Cui Xi'an Jiaotong University
Xiaoping Yang Xi'an Jiaotong University
Xiang Ma Xi'an Jiaotong University
Ziyi You Xi'an Jiaotong University
Yonghai Zhang Xi'an Jiaotong University
Jinjia Wei Xi'an Jiaotong University