Bioinspired heat exchangers based on triply periodic minimal surfaces for supercritical CO₂ cycles

The supercritical carbon dioxide (sCO₂) based Brayton cycle is a proposed alternative to replace conventional Rankine cycles in terms of high cycle efficiency, compact turbomachinery and heat exchangers. In the sCO₂ cycle, however, the existing heat exchangers have been challenged by large portion of heat transfer (approximately 60–70% of total cycle heat transfer) and high cycle efficiency required. In the present study, two novel heat exchangers were proposed by utilizing triply periodic minimal surface (TPMS) structures. i.e. the Gyroid structure and Schwarz-D surface, to enhance heat transfer and improve cycle efficiency. TPMS structures are a class of structures composed of two distinct inter-penetrating volume domains separated by an area-minimizing wall, which have been observed as biological membranes and co-polymer phases. Two heat exchangers along with a reference printed circuit heat exchanger (PCHE) were investigated numerically by computational fluid dynamics simulations when the hot and cold sCO₂ fluids pass through them at various Reynolds numbers. Effects of geometrical shapes and Reynolds number on the hydraulic and thermal performances were identified. It was demonstrated that two heat exchangers with TPMS can improve overall thermal performance by 15–100%, and the Nusselt number is raised by 16–120% for a given pumping power in comparison with the PCHE. Hence, heat exchangers with TPMS have a very good potential to enhance sCO₂ cycle efficiency.