Thermal stratification mechanism analysis of new molten salt storage tank system based on spiral infusion structure

Abstract

Against the backdrop of challenges posed by conventional energy supply and the inherent intermittency of renewable sources, the development of high-performance energy storage technologies has become paramount for balancing energy supply and demand dynamics. This manuscript introduces a novel thermal storage system integrating a spiral folding plate with a stratified tank, where induced spiral molten salt flow enables bidirectional regulation to optimize both thermal stratification and flow characteristics. The study comprehensively evaluates the performance optimization of the spiral folding plate molten salt thermal storage tank through numerical simulations. The helical flow channel design demonstrates dual-regulation advantages: during charging, it suppresses mixing to refine temperature stratification from 3 to 5 distinct layers (deviation <5 %) while maintaining a 1.7 m thermocline stability. During discharging, secondary vortices (diameter ≈1/3 tank radius) actively enhance mixing, reducing the high-temperature zone from 100 % to <5 % within 60 min. Geometric parametric analysis reveals: (1) Increasing height-to-diameter ratio (h/d = 1 → 2.5) enhances helical stability, reducing thermocline thickness by 40 % (with a local temperature difference below 15 K) and improving charge/discharge efficiency by 7.1 %/7.8 %, with h/d≈2.5 tanks achieving 65 % initial discharge energy release; (2) Optimal inclination angle (5°) achieves a 92.5 % discharge efficiency with 3070 s/3030 s charge/discharge times, whereas angles > 30° reduce efficiencies by 1.2 %/3.2 % and induce flow recirculation; (3) Spiral fractions of 10 ∼ 12 maximize performance with a 4.2 % charging efficiency gain and a 35 % flow resistance reduction, while fractions > 20 cause flow resistance surges and thermal anomalies.