Performance analysis and structural optimization of NaK78-He plate-fin heat exchanger for space nuclear reactor power systems based on a Q3D numerical method

Abstract

In space nuclear power systems, heat exchangers account for more than 50% of the total system weight. To minimize both weight and volume, this study selected a compact plate-fin heat exchanger (PFHE) as the NaK⁷⁸-He heat exchanger for the space nuclear power system. Computational fluid dynamics (CFD) simulations were employed to analyze the velocity distribution at the NaK⁷⁸ inlet side of a typical PFHE structure, and the channel design was optimized to enhance heat transfer and reduce pressure loss. To investigate the performance variations of the PFHE and further decrease its weight and volume, a simplified and accurate quasi-three-dimensional (Q3D) numerical calculation method was proposed. This method was combined with a genetic algorithm to optimize the PFHE’s size parameters. Results indicated that the uneven flow distribution on the NaK⁷⁸ side could reduce the heat flow by approximately 10% and increase pressure loss by over 500%. The optimized PFHE significantly improved flow uniformity, reducing the standard deviation of velocity distribution from 1.11 to 0.26. Furthermore, after optimization using the genetic algorithm, the PFHE achieved a 23.47% reduction in overall volume and a 22.38% decrease in weight. This study provides valuable insights for optimizing heat exchangers in space nuclear power systems and presents an efficient, rapid, and accurate method for performance evaluation and optimization in engineering applications.