Experimental and Numerical Study on Stratification Characteristics of a Water-Based Thermal Energy Storage Tank under Different Charging Directions and Flow Rates

This study examines the thermal stratification characteristics of a water-based thermal energy storage (TES) tank under various charging directions and flow rate conditions. A lab-scale TES system was designed using Froude similarity, based on a prototype intended for integration with a 1000RT heat pump system. We conducted experiments and CFD simulations using a 2-D axisymmetric model (Ansys Fluent) to validate thermal behavior and assess stratification performance. Charging tests were performed for both top-to-bottom and bottom-to-top configurations at flow rates of 127 LPM and 215 LPM. The results indicated that top charging effectively maintained a distinct thermocline region, with a Richardson number up to five times higher than that of bottom charging, demonstrating stronger stratification.<br/>While increased flow rates accelerated charging, they also weakened stratification due to enhanced momentum effects. The discharging tests confirmed that the outlet temperature remained stable at 43℃ for the designed discharging duration before beginning to decrease. These findings underscore the importance of inlet design and flow control in enhancing TES tank performance and sustaining thermal stratification.