Thermal and mechanical investigation of TPMS-based heat exchangers for supercritical CO2 power cycles

The advent of additive manufacturing has provided strong incentives to explore complex designs in engineering. In the field of heat exchangers, Triply Periodic Minimal Surface (TPMS) structures have recently attracted significant interest due to their increased heat transfer surface area and enhanced thermal performance. The present study focuses on a heat exchanger used as a pre-cooler in supercritical carbon dioxide (S-CO 2 ) power cycles and investigates both the heat transfer performance and mechanical behavior of two TPMS geometries. Three-dimensional conjugate heat transfer simulations, along with mechanical finite element and experimental analyses, were conducted on Schwarz Primitive and Gyroid lattice geometries with varying volume fractions (VF) and aspect ratios (AR). Building on this comprehensive approach, the novelty of this work lies in addressing the current lack of systematic investigations into the thermo-hydraulic and mechanical performance of TPMS structures for S-CO 2 power cycles, thereby enabling the development of advanced heat exchangers for this emerging application. The analyses were conducted over a Reynolds number range by varying S-CO 2 inlet temperature from 30 °C to 60 °C, as the hot fluid, while water was used as the coolant under fixed operating conditions. From a thermal-hydraulic perspective, Nusselt number, friction factor, heat transfer coefficient, and performance evaluation criterion (PEC) were systematically analyzed for the different geometries. The results show that the Gyroid geometry generally exhibits higher Nusselt numbers and PEC values, with a markedly higher heat transfer coefficient compared to the Schwarz Primitive geometry, at the cost of a slightly higher friction factor and pressure drop. Furthermore, increasing the volume fraction or decreasing the aspect ratio, corresponding to a more compressed geometry, reduces performance, as insufficient mixing length limits effective scouring of the heat transfer surfaces. For Gyroid geometries, a distinct enhancement of approximately 34% in the Nusselt number is observed at lower volume fractions, with VF = 0.2 outperforming VF = 0.4. A detailed analysis showed that the underlying physical mechanism is associated with enhanced flow mixing, as lower AR values and higher VF promote stronger flow redirection and increased turbulence intensity within the domain, thereby improving convective heat transfer. In addition, both numerical and experimental modal analyses demonstrated that the fundamental bending frequencies increase systematically with increasing aspect ratio and volume fraction, attaining values exceeding 10 kHz for high-stiffness configurations. Conversely, reductions in volume fraction result in downward frequency shifts on the order of approximately 10%–15%. The approach and results provide a reference data and foundation for the further development of innovative compact heat exchangers for S-CO 2 power cycles, specifically for waste heat recovery applications, where compactness and low weight are of great importance. • TPMS geometries parameterized by volume fraction and aspect ratio. • Experimental and numerical modal and thermal hydraulic analyses were conducted. • As S-CO 2 pre-coolers, thermal performance is sensitive to geometrical parameters. • Gyroid outperforms Schwarz Primitive as S-CO 2 pre-cooler. • A strong sensitivity of heat-transfer performance to porosity is identified.