Computational fluid dynamics challenges in packed bed of rocks: a technical note on volume averaging method

Packed beds of crushed rocks are fundamental components in thermal energy storage systems, particularly those utilizing air as the working fluid. Despite their cost-effectiveness and favorable thermal properties, modeling these systems presents significant challenges due to the irregular geometry of crushed rock particles and the extensive scales of the beds. This technical note investigates volume-averaged computational fluid dynamics (CFD) modeling techniques for packed beds, focusing on the complications introduced by irregular particle shapes. Various correlations and models are evaluated, highlighting how different Reynolds number definitions influence pressure drop and heat transfer coefficient estimations within porous media, as well as the importance of accurate modeling of effective thermal conductivity. Key particle and bed characteristics are identified, and tortuosity emerges as a critical parameter for simplifying pressure drop calculations, though its estimation remains difficult. Our results indicate that conventional models may not fully capture the behavior of packed beds with irregular particles. Accordingly, this note acknowledges the ongoing progress in 3D particle-resolved simulations and promotes further research in this area, which can yield refined correlations for volume-average parameters enabling more precise estimates of tortuosity and, consequently, more efficient and inclusive designs for packed bed systems with irregular particles. This work provides a methodological guide to advanced modeling techniques for tackling the complexities inherent in real‐world packed‐bed systems with irregularly shaped particles, such as rock‐based thermal energy storage, while noting that the underlying approaches extend well beyond thermal storage application.