Validation of Heat Transfer and Pressure Drop in A Packed Bed of Crushed Rock Thermal Energy Storage System

Concentrated solar thermal energy (CSE) is a clean and sustainable form of energy for power generation and process heat especially in countries with a good solar resource. Thermal energy storage (TES) is required for a continuous output to bridge the intermittent solar resource (the diurnal cycle and cloud events). CSE with TES is cost competitive with solar voltaic energy with battery storage when storage time exceeds 6 h or more. Using air as a heat transfer/working fluid, crushed rock TES offers a low‐cost CSE solution with minimal environmental impact. The irregular shape of crushed rock particles leads to a pressure drop and heat transfer coefficient that depends on the orientation of particles relative to the main flow direction. Crushed rock results in anisotropic pressure drop and heat transfer in packed beds, invalidating the standard isotropic correlations for packed beds of spheres. This paper discusses particle characterization and the derivation of a representative particle shape, physical experiments with crushed rocks and the representative particle, as well as discrete element (DEM) and computational fluid dynamics (CFD) modeling of packed beds of representative particle shapes done at Stellenbosch University to find a tensor formulation for the pressure loss and heat transfer coefficients for a packed bed of crushed rock. The work concludes with the experimental validation of the tensor model against a packed bed of crushed rock particles.