Experimental Investigation on Anisotropic Effective Thermal Conductivity of Pebble Bed

The thermal properties of the pebble beds have a significant impact on the temperature profile of the Helium Cooled Pebble Bed blanket and the extraction of heat from the pebble beds to the coolant. The effective thermal conductivity of pebble bed has been modeled as the isotropic one. However, the isotropic thermal conductivity inherently can be achieved only the case with perfectly isotropic arrangement which is difficult to realized in the actual blanket device. In this paper, the relation between effective thermal conductivity tensor and fabric tensor in 2D pebble bed is investigated experimentally. It is cleared that the effective thermal conductivity tensor is proportional to the structural anisotropic tensor. And, the anisotropic feature is quite different between core region and near wall region, so that it is suggested that modeling of the effective thermal conductivity tensor of the pebble bed should be separately carried out at least in above two regions.