As an essential component of the SCO2 recompression Brayton cycle, the recuperator has a significant impact on the efficiency and stability of the entire cycle system. The printed circuit heat exchanger (PCHE) is the most suitable heat exchanger for the recuperator in the SCO2 recompression Brayton cycle. To investigate the effects of the structural parameters of the asymmetric airfoil fins on the thermo-hydraulic performance of the PCHEs, simplified three-dimensional numerical simulation models for the PCHE with National Advisory Committee for Aeronautics (NACA) 85XX series asymmetric airfoil fins were built. An optimization method combining an orthogonal experiment and a quadratic polynomial surrogate model with a multi-objective genetic algorithm was proposed to obtain the optimal structural parameters. The results show that the fin thickness lb has the most significant effect on the comprehensive performance and fluid flow performance, and the transverse spacing lc has the highest influence on the thermal performance. The optimum structural parameters set are a combination of the transverse spacing of 3.9mm, the longitudinal spacing of 11.5mm, and the fin thickness of 0.77mm.

Purpose This paper aims to investigate the effects of different volume fractions of Al2O3-water nanofluid on flow and heat transfer under chaotic convection conditions in an L-shaped channel, comparing the difference of numerical simulation results between single-phase and Eulerian–Lagrangian models. Design/methodology/approach The correctness and accuracy of the two calculation models were verified by comparing with the experimental values in literature. An experimental model of the L-shaped channel was processed, and the laser Doppler velocimeter was used to measure the velocities of special positions in the channel. The simulated values were compared with the experimental results, and the correctness and accuracy of the simulation method were verified. Findings The calculated results using the two models are basically consistent. Under the condition of Reynolds number is 500, when the volume fractions of nanofluid range from 1% to 4%, the heat transfer coefficients simulated by single-phase model are 1.49%–25.80% higher than that of pure water, and simulated by Eulerian–Lagrangian model are 3.19%–27.48% higher than that of pure water. Meanwhile, the friction coefficients are barely affected. Besides, there are obvious secondary flow caused by lateral oscillations on the cross sections, and the appearance of secondary flow makes the temperature distributions uniform on the cross section and takes more heat away, thus the heat transfer performance is enhanced. Originality/value The originality of this work is to reveal the differences between single-phase and two-phase numerical simulations under different flow states. The combination of chaotic convection and nanofluid indicates the direction for further improving the heat transfer threshold.

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