Study of heat transfer enhancement surfaces generated by additive manufacturing techniques

• Main Author: Wong, Kin Keong
• Other Authors: Leong Kai Choong
• Format: Theses and Dissertations
• Language: English
• Published: 2019
• Subjects: DRNTU::Engineering::Mechanical engineering::Fluid mechanics; DRNTU::Engineering::Mechanical engineering::Prototyping
• Online Access: https://hdl.handle.net/10356/105249; http://hdl.handle.net/10220/47827
• Institution: Nanyang Technological University

Thermal management in electronic devices is becoming increasingly challenging due to the higher heat outputs from the increased packing density of transistors. Nucleate boiling has been shown to be an effective cooling scheme for high heat flux removal. In recent years, the use of commercial porous foams has been demonstrated to have potential for nucleate boiling applications due to their high surface-to-volume ratio. However, there are limitations in terms of pore design and challenges of random pore distribution and poor inter-connectivity. These issues can be overcome by fabricating metallic engineered porous structures using the Selective Laser Melting (SLM) technique, which is a type of additive manufacturing. The objectives of this thesis are to investigate the nucleate pool and flow boiling enhancements using engineered three-dimensional (3D) porous substrates. The use of SLM allows highly customised and complex porous substrates to be fabricated with high dimensional accuracy. Heat transfer performances of these substrates were then investigated using a thermosyphon for pool boiling and a two-phase flow facility for flow boiling. The dielectric fluid FC-72 was used as the coolant due to its electrical and chemical compatibility with electronic devices. For pool boiling, two different designs of porous structures of octet-truss and re-entrant geometries were fabricated. The experimental results show enhanced nucleate boiling heat transfer due to the increased nucleation site density and capillary-assisted suction. Using high speed photography, the boiling mechanisms in 3D porous structures were studied and analysed. For flow boiling, engineered 3D substrates with hollow spherical features were fabricated. Three substrates were tested in a two-phase flow facility. The effects of mass flux and substrate type were investigated. Using high speed photography, it was shown that the heat transfer mechanism was nucleate boiling as opposed to convective boiling dominated.