Parametric numerical study on flow and heat transfer characteristics of a steam-molten salt spiral-wound heat exchanger

In a deep peak-shaving system of coal-fired units coupled with main steam extraction and molten salt thermal storage, the flow and heat transfer behavior of steam and molten salt within the core heat exchange equipment directly affects the system performance. In this study, a steady-state single-phase numerical simulation method was employed to systematically analyze the effects of key geometric configuration parameters and operating parameters on the thermo-hydraulic characteristics of high-pressure superheated steam on the tube side and a novel low-melting-point molten salt on the shell side in a spiral-wound heat exchanger (SWHE), and quantitatively evaluated the performance based on the comprehensive performance evaluation criterion ( PEC ). The results indicate that geometric parameters mainly affect the heat transfer coefficient and pressure drop by altering the flow area on both sides. Adopting a small tube diameter, a small first-layer winding diameter, and moderate layer spacing and tube spacing benefits the thermo-hydraulic performance on both sides, with a more pronounced effect on the shell side. Operating parameters determine the performance on both sides primarily through their respective working conditions. Increasing steam flow rate or pressure, or reducing the degree of superheat, enhances heat transfer on the steam side, while pressure drop is mainly influenced by flow rate and pressure. Increasing molten salt flow rate enhances heat transfer and increases pressure drop, while raising the molten salt temperature benefits heat transfer but has a minor effect on pressure drop. Furthermore, the two sides interact through thermal coupling. Reducing steam pressure or increasing the degree of superheat helps optimize performance on the molten salt side, whereas increasing molten salt flow rate enhances steam-side heat transfer, and raising the molten salt inlet temperature suppresses heat transfer. Based on the PEC analysis, operating conditions with higher pressure and larger flow rates can achieve synergistic optimization of the overall performance on both sides. This study also established reliable flow-heat transfer correlations, with average fitting errors of ±5% and ± 5% for the Nusselt number and friction coefficient on the steam side, respectively, and ± 10% and ± 15% on the molten salt side. These findings provide a theoretical basis for the optimal design and operational regulation of spiral-wound heat exchangers, and provide support for enhancing the peak-shaving flexibility of coal-fired power units.