Design of passive heat sink with enhanced thermal performance and mechanical strength using multi-objective topology optimization

In practical engineering environments, passive heat sinks are often required not only to dissipate heat, but also to withstand external loads and provide structural protection for heat-generating components. This study proposes a thermo-fluid-structure coupled topology optimization framework for the design of thermo-mechanically integrated passive heat sinks under natural convection. An in-house finite element code is developed and numerically assessed over three representative Grashof-number regimes to solve the coupled heat transfer, buoyancy-driven flow, and thermo-elastic problems, while a dual-objective strategy combining weighted logarithmic aggregation with Pareto analysis is introduced to balance the average heat-source temperature and structural deformation. Three regime-specific designs are compared with conventional flat-fin, radial-fin, and tree-fin heat sinks using three-dimensional simulations. In the convection-dominated regime, the optimized design reduces the average heat-source temperature by up to 0.79 K and the maximum structural displacement by up to 94.0% relative to the referenced designs. Load-customization studies further demonstrate the flexibility of the proposed framework to spatially varying thermal and mechanical conditions, while the open-boundary optimization studies show its ability to adapt the topology to ambient-fluid entrainment. Overall, these results demonstrate that the primary advantage of the proposed method lies in improving the thermo-mechanical trade-off, with modest yet consistent thermal improvements accompanied by substantial enhancements in structural stiffness under different operating conditions.