Numerical Investigation of Aspect Ratio Effects on Thermal Stratification and Efficiency of a Pressurized Thermal Storage Tank

This study systematically investigates the effect of aspect ratio (AR) on the thermal performance of a pressurized single‐tank thermal storage system through numerical simulation. Five AR values ranging from 1.2 to 2.5 are evaluated, focusing on key performance indicators including thermal stratification evolution, storage efficiency (), and effective storage volume (). To quantitatively elucidate the mechanisms governing thermocline stability, the Richardson number (Ri) and Péclet number (Pe) are introduced as a unified analytical framework. Results show that increasing AR improves thermal stratification and significantly enhances . Ri increases monotonically from 299 to 487 with AR, confirming that buoyancy forces strengthen with tank slenderness, while Pe rises from 6.45 × 10 6 to 10.50 × 10 6 , indicating sustained convective dominance that effectively counters diffusive broadening. Furthermore, increases substantially with AR, suggesting that a higher AR improves both the quality and quantity of usable storage. Overall system performance is optimized within the AR range from 2.0 to 2.5, although excessively high AR values may induce flow instability. Therefore, AR ≈ 2.0 is recommended to balance thermal performance and operational stability. This study provides theoretical insights and quantitative design guidance for the geometric optimization of single‐medium water thermal storage tanks.