Thermal performance of conduction and forced convection in three-dimensional printed lattice structures

• Main Author: Zhou, Yi
• Other Authors: Fei Duan
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2022
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/162667
• Institution: Nanyang Technological University

The lattice structure is promising for the application as heat exchange media due to its porous and controllable geometric characteristics. The recent developments in three-dimensional (3D) printing technology make the post-process-free and eco-friendly fabrication of complex-shaped lattice structures possible, while the potential of 3D printing for manufacturing thermally used lattice structures has not been explored. In this study, different types of lattice structures are designed and developed for analyzing and further controlling the thermal performance in conduction and forced convection. Based on the findings from thermal performance analysis, the lattice structure is integrated with a conformal cooling channel design to improve the productivity of plastic injection molding. The first effort of this study is to employ experimental and numerical methods to study the steady-state thermal conduction mechanism in lattice structures used as lightweight materials. A conjugated 3D heat transfer model accounting for the flow pattern of lattice structure coupled air has been built. The quantitive agreement on effective thermal conductivity is observed by comparing the experimental and simulation results. The effects of lattice structure design variables on the conductive heat transfer performance are analyzed in detail. The results reveal that either decreasing the porosity or specific surface area strengthens the conductive heat transfer in the specific typed lattice structure. The effective thermal conductivity can also be adjusted by varying the cross-section area along the main heat conduction direction, which is firstly found in the thermal conduction study. The analysis of parameter studies provides direct and effective methods for controlling the thermal conduction performance of lattice structures by setting the structure design variables. The second effort of this study is to experimentally and numerically investigate the hydraulic and thermal characteristics of different lattice structures in air-forced convection. A 3D steady-state conjugated heat transfer model has been developed, in which incompressible turbulent airflow is defined. The simulated pressure drop gradient values fit well with the experimental ones, which support the effectiveness of experiments and simulation models meanwhile. The numerically reproduced temperature and velocity contours visually present the temperature distributions in different lattice structures and flow motions in the coupled air, which are found in agreement with the experimentally derived orders of convective heat transfer efficiency and fluid media transfer capability. The lattice structures with a larger inter-facial surface area and a more complex topology exhibit better convective heat transfer capability, while the one with a larger open area ratio performs lower flow resistance. The findings benefit the heat exchanger design by providing scientific improvement fundamentals on lowering the pumping power needed and enhancing the forced convective heat transfer efficiency. Finally, based on the results from conductive and forced convective thermal performance investigations, lattice structures are integrated into the conformal cooling channel design in a specific plastic injection mold for balancing the objectives of minimum plastic cooling time, minimum plastic surface temperature non-uniformity, and minimum pressure drop from the coolant inlet to the outlet. The channel dimensions are optimized and determined by the multi-criteria decision making approach, and then both experimental and numerical investigations are performed on the 3D printed molds with optimized conformal cooling channels. A 3D transient conjugated heat transfer model has been developed to simulate the cooling process of plastic, which is validated by experiments in terms of pressure drop and cooling time. The integration of lattice structures shortens the cooling time dramatically by enhancing conductive and forced convective heat transfer efficiencies in channels at the cost of slightly increased temperature non-uniformity and pressure drop. The use of lattice structures in conformal cooling channel design has been proved effective for promoting the productivity of plastic injection molding, hence the lead time and cost are reduced significantly. To sum up, the lattice structure is a promising solution for thermal management in which the controllable thermal performance of conduction and forced convection is wished. Future recommendations call for utilizing 3D printing technology to facilitate the innovative designs and fabrications of lattice structures in broadened thermal applications.