Numerical Simulation Study of Built-In Porous Obstacles to Improve the Thermal Stratification Performance of Storage Tanks

Thermocline storage tanks are critical components in energy storage systems for solar renewable energy utilization. The use of thermal stratification of the working fluid within the storage tank for energy storage is a pivotal technology in these systems. Effective thermal stratification can significantly enhance energy storage efficiency, meet a broader range of user demands, and improve the overall performance of the storage tank. Therefore, enhancing the energy storage efficiency of storage tanks is an essential objective. To promote internal temperature stratification within the tank, this study introduces a porous obstacle designed to improve the tank’s internal structure. A comparative analysis was conducted with tanks featuring different structural configurations. Using the commercial finite element software ANSYS, an unsteady Computational Fluid Dynamics (CFD) model was formulated to simulate the energy discharge process of five different tank structures under various operating conditions. By analyzing the internal temperature distribution, thermocline thickness, dimensionless exergy efficiency, and flow field trajectories, the stratification characteristics were determined. The results indicate that the porous obstacle significantly enhances stratification compared to the perforated plate obstacle. At a flow rate of 0.3 m/s, the thermocline thickness in traditional tanks and tanks with perforated plate obstacles is 42% and 14.3% greater, respectively, than in tanks with porous obstacles. Additionally, the study demonstrates that temperature stratification is more pronounced when the porous obstacle is positioned closer to the tank’s bottom, with the optimal configuration being the placement of porous obstacles near both the top and bottom of the tank. At a flow rate of 0.3 m/s, the thermocline thickness in tanks with porous obstacles only at the bottom and middle is 17% and 133% greater, respectively, than in tanks with porous obstacles at both the top and bottom.