Abstract
Thermal stratification strongly affects the efficiency and operational reliability of sensible thermal energy storage (TES) tanks in energy systems. This study numerically investigates the combined influence of inlet configuration and mass flow rate on the charging performance of a vertical cylindrical TES tank (H = 3 m, D = 1 m) using transient CFD simulations. Five inlet designs—open, orifice, groove, shower, and shower-groove are analyzed at three flow rates: Q1 = 0.0003 m3/s, Q2=Q1/2, and Q3=Q1/3. System performance is evaluated using key thermal and stratification metrics. Increasing the flow rate from Q3 to Q1 enhances convective heat transfer and energy and exergy efficiencies, but significantly intensifies mixing and degrades thermal stratification. At Q1, the groove inlet achieves the highest capacity ratio and exergy efficiency (0.87), while exhibiting increased mixing. Reducing the flow rate to Q2 and Q3 limits inlet-induced momentum, leading to improved stratification for all configurations. The shower-groove inlet reaches a maximum stratification level (tail factor) of 1.13 at Q3, indicating superior thermal layering, albeit with lower energetic efficiency (≈0.40–0.45). The groove inlet provides the best overall compromise at Q2, combining high efficiency with stable stratification. These results demonstrate a clear efficiency-stratification trade-off and highlight the importance of selecting inlet-flow combinations according to application-specific objectives.