Numerical investigation of flow and heat transfer characteristics of supercritical CO2 in metal foam for Brayton cycle heat exchangers

Abstract

The supercritical CO 2 (sCO 2 ) Brayton cycle offers great potential for compact, high-efficiency power systems, but conventional heat exchangers struggle to meet extreme thermal demands under high-parameter conditions. Open-cell metal foams offer a promising solution for heat transfer enhancement, yet their complex pore architecture poses major challenges for pore-scale flow analysis, particularly with sCO 2 as the working fluid. This study presents a systematic CFD investigation of the flow and thermal-hydraulic mechanisms of sCO 2 in copper foam tubes based on the Kelvin tetrakaidecahedron topology. Simulations were performed across pore densities (10–40 PPI), porosities ( ε = 0.95–0.974), and inlet velocities at 600 K inlet temperature and 15 MPa outlet pressure. Periodic pressure attenuation is shown to arise mainly from skeletal impingement, interfacial friction, and leeward-side vortex losses, with the unit pressure drop at ε = 0.95 exceeding that at ε = 0.974 by over 66%. A Forchheimer-based correlation was developed for tetrakaidecahedron foam at ε = 0.974. Metal foam substantially enhances sCO 2 convection through its large specific surface area and turbulence promotion; the Colburn j at 40 PPI exceeds that at 10 PPI by 36.9% at low velocities, with this advantage diminishing at high velocities due to turbulence saturation. Using a comprehensive thermal-hydraulic factor j / f , the optimal configuration is identified as ε = 0.974 and 40 PPI, achieving the best balance between heat transfer and flow resistance at low to moderate velocities. These findings provide predictive tools and a theoretical basis, compact porous media heat exchangers in sCO 2 Brayton cycle systems.