Thermohydraulic Characteristics of Supercritical CO₂ Flowing in Printed Circuit Heat Exchanger With Large Eddy Simulation Available to Purchase

Printed circuit heat exchanger (PCHE) is a promising candidate of supercritical CO₂ (S-CO₂) Brayton cycle in the IV nuclear reactor with high efficiency, compactness and high resistance of temperature and pressure. In this paper, model of zigzag PCHE (D = 2.0 mm, L_p = 7.24 mm and θ = 100°) was simulated under the precooler condition near and away pseudo-critical region with S-CO₂ and water as hot and cold fluid respectively. Method of large eddy simulation (LES) was applied to investigate the local performance of S-CO₂ affected by both of complicated structure and drastic properties variation. The results showed that in the local position of a pitch, temperature and velocity on cross-section presented strong nonuniformity due to the disturbance of corner and symmetry on the side of corner, which showed heat transfer enhancement or weakness on different locations. Meanwhile, the turbulent structure of S-CO₂ showed a periodic characteristic among pitches without influence by the drastic change of thermo-physical properties. Based on the results, two flow regions, convection region and mixed region were defined by dividing the local pitches. Combined with the vortex structure analysis using Q criterion, it was found that the mixed region presented more intensive vortex distribution and thus showed a higher heat transfer performance and flow resistance while convection region showed the opposite trend. Therefore, a fluctuation changing curve along the flow direction were observed on heat transfer efficiency and friction factor due to different characteristics of two regions.