Analysis of Near-Wall Pebble Bed Thermal Conductivity for Energy Applications

Pebble beds have been employed in thermal storage and energy systems, where they are typically used to promote heat exchange in high-temperature environments. Understanding the heat conduction of the entire pebble bed could aid in the material selection of the pebbles themselves and structural components, system design, and safety monitoring. However, the thermal conductivity of pebble beds can change significantly near geometric boundaries. Using a complex multilayer analytical model in conjunction with a line source probe, we found a substantial increase in the thermal conductivity of a sintered bauxite pebble bed in the near-wall region (7.6 W m^-1 K^-1) compared to the bulk (0.59 W m^-1 K^-1). We investigated this difference by comparing porosity results, acquired with micro-CT, of 33.18 and 33.31% at approximately one pebble width surrounding the probe (near-wall) and the bulk of the pebble bed, suggesting that the thermal conductivity is largely altered by thermal contact resistance in the near-wall regime.