Dynamic characteristics of solid packed-bed thermocline tank using molten-salt as a heat transfer fluid

Thermocline characteristics and the discharge performance of a molten-salt packed-bed energy storage system are analyzed numerically. For this purpose, a transient two-dimensional model based on local non-equilibrium thermal theory in a porous medium is developed. Three different solid fillers are utilized, including that of quartzite rock, slag pebbles, and alumina ceramics. Molten-salt serves as a heat transfer fluid (HTF). The effects of fluid inlet flow rate and the particle size diameter on the thermocline thickness through temperature profiles of packed-bed systems have been investigated. The discharging power is discussed in a detailed description of various operating conditions through the discharge outlet temperature stability period. The results obtained are compared with that of the pure molten-salt tank. It is revealed that the thermocline thickness of the molten-salt packed-bed tank is higher than that of pure molten-salt tank, while the latter is better in thermal stratification. As the inlet flow rate increases, both the discharging power and thermocline thickness increase. The results also indicated that decreasing particle size diameter, results in a decrease in thermocline thickness, and the discharging performance becomes more stable. Slag pebbles as a filler material is more effective than quartzite rock in thermal energy storage (TES). The results can be beneficial for the design and optimization of the packed-bed thermocline tank.