Numerical investigations on serpentine channel for supercritical CO2 recuperator

Highlights: • The secondary flow enhances heat transfer for improved field synergy in serpentine channel. • The vortexes take turns at dominating local secondary flow in serpentine channel. • The smaller curvature and larger camber result in the better overall performance at low Re. • The vertical ellipse has the less flow resistance due to the reduced disturbance on flow. -- Abstract: The Printed Circuit Heat Exchanger (PCHE) in supercritical carbon dioxide (S-CO₂) Brayton cycle has a significant effect on the efficiency, compactness and stability of system. To improve the performance of PCHE with serpentine channel, the present work numerically investigated the mechanism of convective heat transfer of S-CO₂ in serpentine channel under turbulent condition with inlet Re = 9500–30000, and explored the effects of geometrical parameters on the thermohydraulic performance. The secondary flow motion and the effect of Prandtl number were investigated, and the curvature diameter (D), the camber (C) and the cross-sectional shape were compared and discussed. It was found that high Prandtl number enhances the heat transfer performance significantly near the pseudocritical point, and the secondary flow improves the field synergy and enhances the convective heat transfer in serpentine channel. With smaller curvature diameter or larger camber, the serpentine channel has better overall performance and smaller entransy dissipation-based thermal resistance at relatively low Reynold number, while the thermohydraulic performance becomes worse in the case of relatively high Reynold number due to the considerable flow resistance. Among the numerous cross-sectional shapes, the circle has the best heat transfer performance and the vertical ellipse has the least flow friction.