Optimization of Higher-Order Harmonic Surface Tessellations for Additively Manufactured Air-to-Air Heat Exchangers: A Numerical Study

Air-to-air heat exchangers are vital for energy recovery and thermal management but often suffer from reduced effectiveness, high pressure losses, and increased pumping power in conventional designs. Advances in additive manufacturing have enabled nature-inspired geometries, such as lattice and triply periodic minimal surface (TPMS) structures, which enhance heat transfer through complex first-order surfaces but are frequently associated with excessive pressure drops. This study proposes an optimized higher-order harmonic heat transfer surface tessellation developed through an optimization framework integrating analytical and numerical methods. The goal is to improve the overall thermal–hydraulic performance of the heat exchanger over a range of operating conditions. Results of the sensitivity analysis show that secondary surface modification of this type can yield a significant increase in effectiveness reaching up to 14%, although with an associated increase in the pressure drop. Additionally, we show that the optimized second-order harmonic-type structure achieved relatively higher effectiveness for comparable but slightly lower pressure drop than the gyroid structure across the flow regimes considered. While the gyroid structure outperformed the optimized harmonic-type structure in terms of the fin geometry heat transfer efficiency assessed based on the London goodness factor, j/f1/3 by a factor of 1.9, the optimized harmonic-type structure had relatively higher energy efficiency than that of the gyroid structure across the entire spectrum of operating conditions reaching up to a factor of about 1.6 in the laminar flow regime. The findings from this study demonstrate a balanced pathway for additively manufacturable, high-performance air-to-air heat exchangers, offering compact, energy-efficient solutions for applications in building ventilation, aerospace, and electronics cooling.