Homogenization-based optimization of wall thickness distribution for TPMS two-fluid heat exchangers

Triply periodic minimal surface (TPMS) structures are attractive for high-performance heat exchangers (HXs) owing to their continuous flow pathways and high surface-area-to-volume ratios. In addition, spatially graded wall thickness offers further potential to enhance thermal–hydraulic performance. This study proposes an effective porous media model for TPMS two-fluid HXs, in which effective heat-transfer coefficients derived from unit-cell CFD simulations are incorporated to represent heat exchange between the fluid phases and the solid wall. The proposed model enables macroscopic evaluation of wall-thickness effects on HX performance without resolving the complex TPMS geometry, while reducing the computational cost by approximately 260 times compared with full-scale simulations. By integrating the model into a density-based topology optimization framework, a rapid and practical method for optimizing wall-thickness distribution in TPMS HXs is established. Full-scale numerical simulations of the optimized-thickness design for a gyroid two-fluid HX show a 12.2% improvement in the performance evaluation criterion (PEC) compared with the uniform-thickness design. The improvement arises from the optimized non-uniform wall thickness, which directs more flow toward the core ends and enhances velocity uniformity. As a result, heat transfer is enhanced at the core ends, leading to more effective utilization of the entire HX core and improved overall thermal performance.