Analysis and Optimization of Thermal Storage Performance of Thermocline Storage Tank with Different Water Distribution Structures

Energy storage is essential for solar energy utilization, and thermocline storage tanks are commonly used. To improve temperature stratification and storage efficiency, we investigated the effect of different water distributor configurations on tank stratification. We numerically analyzed the heat storage processes in hot water tanks with three water distribution configurations: star, antenna, and octagonal. Temperature stratification was evaluated based on thermocline thickness and storage efficiency. Thermal storage efficiency improves by 0.45% when the outlet direction of the water distributor matches the fluid’s motion direction during natural stratification. The energy storage process is categorized into three stages based on efficiency changes, with different factors affecting efficiency at each stage. In the initial stage, antenna-type and octagonal water distribution improve temperature uniformity along the axial section, reduce thermocline thickness, and enhance stratification. Final efficiency during this stage is primarily influenced by energy loss resulting from the mixing of hot and cold water. In the development stage, energy storage efficiency decreases mainly because the lower boundary of the thermocline reaches the exit, causing partial discharge of hot water. Among the three configurations, the octagonal water distribution exhibits the lowest energy loss, 6.4% lower than that of the star-type distribution.