Numerical Investigation of Packing Structure and Bed Geometry Effects on Heat Transfer in Granite Rockbed Thermal Energy Storage Systems

The thermal performance of a packed rockbed thermal energy storage system depends not only on particle properties but also on the spatial arrangement and overall geometry of the storage bed. This paper extracts the thermal and packing-structure component of an MSc numerical study carried out using ANSYS Fluent 19.2. Equal-volume cubical, cylindrical and conical/truncated-conical rockbed configurations were investigated using granite and air. The simulations used an inlet temperature of 500 K, a mass flow rate of 0.15 kg/s for the reported geometry comparison, and a particle-size range of 20–60 mm for the broader study. For the 40 mm particle comparison, the reported heat-transfer rates were 16.599 kW for the cube, 18.108 kW for the cylinder and 19.617 kW for the cone. The conical configuration therefore produced the largest reported heat-transfer rate among the three 40 mm cases, while the cube produced the lowest. The temperature contours show the development of a thermal front, with the hot region advancing from the inlet toward the colder downstream region. The reported outlet-temperature series decreased from 500 K at the start of the plotted charging history to 415 K at 3600 s. The results demonstrate that bed geometry and packing arrangement can materially alter thermal response and should be evaluated together with hydraulic resistance when designing rockbed thermal storage.