Optimizing void fraction for enhanced heat transfer in lab-scale PCM packed-bed thermal energy storage systems

Abstract

Abstract This study investigates the critical influence of bed-packing architecture on the transient fluid and phase-change kinetics of a latent heat packed-bed thermal energy storage (TES) system. Utilizing a validated two-dimensional computational fluid dynamic model, the charging behavior of an insulated tank containing spherical phase change material (PCM) capsules is systematically analyzed. The thermocline behavior during charging and discharging is examined. The system performance is evaluated under three distinct structural packings: ϵ = 0.36, ϵ = 0.49, and ϵ = 0.60. The simulation results demonstrate that increasing porosity from 0.36 to 0.60 accelerates the charging speed by 20.8%, accompanied by a 33.3% increase in the rate of temperature rise in the HTF and PCM phases. However, the system efficiency was decreased by 0.5%. A porosity of ϵ = 0.49 is recommended as the optimal bed configuration, balancing a high volumetric heat density with a 97.5% charging completion rate and providing a high efficiency of 44.5%. These findings establish clear design guidelines for optimizing the thermal efficiency of packed bed latent TES systems.