Experimental investigation of effective thermal conductivity of packed lithium-titanate pebble bed with external heat source and flow of helium

Packed pebble bed of ceramic solid breeder materials viz. lithium titanate or meta-titanate (Li2TiO3), lithium orthosilicate (Li4SiO4) etc. is being considered for fusion blankets. During the breeding of tritium, helium will be produced and also it is proposed to flow helium from outside through the bed to extract tritium, as well as to remove thermal energy from the bed. Experimental determination of thermal property data of the pebble bed under helium gas flow is important for the blanket design. Such study of determination of effective thermal conductivity with flowing helium condition was not performed previously. Though, it is known that with an increase in gas flow rate, the effective thermal conductivity of pebble bed increases, it is necessary to conduct experiments to know the exact values and the degree of variation. Model and experimental setup used in our previous study was used to for this present work. Effects of process parameters viz., helium gas flow rate, bed temperature, pebble size etc. on the effective thermal conductivity of the bed have been studied. Correlations have been developed from these experimental data to estimate effective thermal conductivity at different particle Reynold's number and bed temperature. It was found that with the use of helium, the effective thermal conductivity of bed increases by many folds. Experimental details and results are discussed in this paper. (C) 2016 Elsevier B.V. All rights reserved.