Topology optimization of microchannel heat sinks for laminar flows of thermal–fluid

• Total dissipation power of flow is constrained to ensure pressure drop. • Thermal efficiency has been enhanced without altering power dissipation. • Thermal performance varies similarly in both two- and three-dimensional cases. • Design efficiency of 3D topology optimization can be improved by 2D topology optimization. In practical applications, the optimized design of microchannel heat exchangers is a result of a proper balance between thermal and hydraulic performances. This suggests that material properties and flow conditions determine the upper limit of the performance of microchannel heat exchangers. Exploring the influence of the material properties and flow conditions on the microchannel heat exchangers is beneficial for establishing more cost-effective solutions in the design process of microchannel heat exchangers, i.e., finding the optimal combination of materials, flow conditions, and microchannel structures. To explore the impact of physical conditions on the thermal performance of an optimized microchannel structure, this study innovatively proposes a single-objective topology optimization method constrained by relaxed fluid energy dissipation. The two-dimensional (2D) and three-dimensional (3D) topology optimization models were systematically analyzed. The numerical results indicate that the fluid energy dissipation constraint is equivalent to the pressure drop constraint. The performance of microchannel structures greatly varies with physical conditions and exhibits similar regularities in 2D and 3D cases. An increase in Reynolds number (Re), an increase in Péclet numbers, a synergistic increase in both numbers, as well as an increase in solid–liquid heat conduction ratio can enhance thermal indicators. In 2D problems, the maximum reductions in objective function are 79.37%, 44.4%, 98.54%, and 99.43%; whereas in 3D problems, the values are 63.64%, 89.67%, 12.08%, and 99.43%, respectively. Based on similar regularities in both 2D and 3D cases, a strategy to improve efficiency of topology optimization design for 3D microchannel heat exchangers is proposed.