A numerical investigation of the influence of an obstacle inside the vertical mantled hot water storage tank on the thermal stratification under discharging operation condition for domestic solar energy applications

• A 3D unsteady CFD model of a mantled hot water storage tank is rigorously validated. • A rigidly mounted internal obstacle acts as a momentum breaker to preserve thermal stratification. • The obstacle reduces the MIX number by up to 75% under high Reynolds number discharging conditions • A novel dimensionless correlation is developed to predict stratification performance. Thermal stratification has a significant effect on the thermal performance of a hot water storage system. To obtain better thermal stratification (TSt), internal mixing must be minimized. One effective method is placing an obstacle inside the tank to break the momentum of the incoming fluid. In the present study, a 3D unsteady CFD model is developed and rigorously validated to investigate the influence of an internal cylindrical obstacle on the thermal performance of a mantled solar domestic hot water storage system (SDHWS) during dynamic discharging operations. The performance is assessed using temperature distribution, consumption water temperature, MIX number, and Richardson number. The findings clearly demonstrate that the internal obstacle acts as a momentum breaker, significantly improving TSt. Quantitatively, the obstacle reduces the MIX number by up to 75% at high inlet velocities (e.g., Re = 1270) and maintains a substantially higher consumption water temperature compared to the baseline case without the obstacle. Furthermore, lower cold water inlet velocities and higher mantle inlet temperatures also enhance the storage system’s performance. Finally, a novel empirical dimensionless power-law correlation is formulated, mathematically revealing that the MIX number is highly sensitive to the inlet flow momentum (scaling with Re 0.62 ), providing a robust predictive tool for the design and optimization of thermal storage tanks.