Study on flow and heat transfer characteristics of helium-xenon mixtures in airfoil-fin PCHEs with different cross-sectional parameters

The airfoil-fin type printed circuit heat exchanger (airfoil-fin PCHE) is ideal as a recuperator in helium-xenon-cooled microreactor power systems, where its performance is crucial for both efficiency and compactness of the system. Many researchers have made significant efforts to improve PCHEs’ performance, particularly in flow and heat transfer. However, few have focused on the quantitative evaluation of coupled heat transfer processes between the cold and hot sides or the effects of cross-sectional parameters, such as shape factor (the height-to-width ratio of the airfoil fin channel) and channel height ratio (the hot-to-cold channel height ratio in airfoil-fin PCHEs). In this paper, a novel dimensionless number Nutotal, derived from boundary layer theory, was proposed to quantitatively assess the coupled heat transfer between the hot channel and the cold. Furthermore, the effects of cross-sectional parameters were numerically investigated so that measures were proposed to improve the performance of airfoil-fin PCHEs. The results indicate that increasing the shape factor from 0.333 to 0.600 enhances thermal performance by 7.632 %–10.169 % compared to the 0.333 value, while further expanding the shape factor to 0.733 only yields an additional 0.655 %–1.726 % improvement, indicating sharply diminishing marginal returns. The height ratio has little effect on coupled heat transfer (<4.122 %) when the total height of the hot and cold side channels is fixed, meanwhile the mass flow rates on both sides are equal. while increasing the hot-side height ratio from 30 % to 70 % can significantly reduces the overall flow resistance (ranging from 9.275 % to 29.268 %). These findings are useful to simplify the design process of helium-xenon recuperators.