Experimental Measurements of the Interface Thermal Conductance of a Lithium Metatitanate Pebble Bed

The thermal properties of the lithium ceramics 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 literature review showed a lack of experimental data on the interface thermal conductance (h) of lithium metatitanate pebble beds, therefore the objective of this study is to present experimental values of h. The measuring technique is based on the principles of steady state and axial heat flow methods. The lithium metatitanate pebble bed is single size (~O1.7-2.0mm pebbles) with a packing fraction of 61%. The values of h were measured at the interface of the pebbles with their container's wall (made of stainless steel 316). The results showed that h increased from 1800 to 5300W/m².K with the increase of the wall temperature from 24 to 570°C. The theoretical values of h, calculated by three models, were compared with the experimental values. The theoretical and experimental values of h showed similar behavior with the increase of temperature. The present values of h will help to create a reliable database of the thermal properties of the lithium ceramics pebble beds.