Comparison of Stratification Performance in Oil-based Thermal Storage Tank for Different Immersed Discharging Coil Configurations

This study investigates the thermal stratification characteristics of a single-medium sensible heat storage tank.The thermal energy storage (TES) system under investigation comprises a vertical cylindrical tank fitted with an immersed discharging coil.The study considers three different discharging coil configurations (helical, conical, and inverted conical).A commercial silicone oil (Hytherm 600) is used as the heat storage medium in the tank, and water serves as the discharging fluid.The thermal characteristics during the simultaneous charging and discharging operation are investigated considering a fixed charging temperature of 90 , an oil flow rate of 1.25 L/min, and two different discharging flow rates (water), 0.5 and 2 L/min, respectively.Results indicate enhanced thermal performance for the helical discharging coil at the discharging flow rate of 2 L/min, with a total discharged energy of 3536.8 kJ, and a discharging efficiency of 54.1%.The highest energy discharged (3546.5 kJ) is realized in the case of the inverted conical coil.However, the losses are higher for this storage configuration, leading to a slightly reduced discharging efficiency (53.6%).The thermocline thickness broadens with increasing water flow rates through the discharging coil side.Eventually, the initial thermocline splits to form a stabilized thermocline thickness of 100 mm in the upper section of the tank for a 2 L/min coil flow rate.