Experimental measurements of the effective thermal conductivity of a simple-cubic packed pebble bed

The effective thermal conductivity represents the overall heat transfer characteristics of a packed bed of spheres and must be considered in the analysis and design of pebble bed High Temperature Gas-cooled Reactor (HTGR). In this study, an experimental facility has been developed to measure the effective thermal conductivity of a simple cubic packed pebble bed. The effects of some key parameters including bed temperature and pebble materials on the effective thermal conductivity of pebble beds are investigated. The wall effect on the effective thermal conductivity is also analyzed. Meanwhile, the experimental results are compared with the ZSK correlation and the ZBS correlation. It is found that the effective thermal conductivity decreases with the increasing bed temperature. Moreover, the effective thermal conductivity of a bed filled with graphite pebbles is about 4 times that of stainless steel pebbles. The experimental results show that there is a reduction in the magnitude of the effective thermal conductivity at the near-wall region. The experimental results fit well with the ZBS correlation at lower temperature. While at the higher temperature, there is an obvious discrepancy between the experimental results and the two correlations.