Effects of solid particle properties on the thermal performance of a packed-bed molten-salt thermocline thermal storage system

• We present a transient two-dimensional dispersion–concentric (D–C) model for the packed-bed thermocline system.
• We investigate the effects of solid particle diameter and particle material on the system performance.
• Heat transfer between solid particles and fluid can be significantly influenced by particle diameter.
• Low thermal conductivity of solid restricts heat transfer between fluid and solid particles with large diameters.

In this study we present a transient two-dimensional dispersion–concentric (D–C) model for heat transfer and fluid dynamics in a packed-bed molten salt thermocline thermal storage system. Based on the developed model, the effects of solid particle properties including particle diameter and particle material on the heat transfer between molten salt and solid particles are investigated with emphasis on detailed temperature distributions within solid particles. The results show that heat transfer between solid particles and molten salt can be significantly influenced by particle diameter. Increasing the particle diameter reduces heat transfer rate between solid particles and molten salt, and finally results in a decrease in the effective discharging time and discharging efficiency. It is also found that the effect of solid material on the thermal performance is influenced by the particle diameter. When particle size is small enough, the efficiency of the thermocline system is nearly independent of the solid material. For large particle diameters, heat discharge rate from solid particles to molten salt may be reduced if the thermal conductivity of solid particle is too low.