Study on the effective thermal conductivity of different packing schemes of tritium breeder pebble beds

A heat transfer analysis model of pebble beds is established based on discrete element method and computational fluid dynamics coupling method (DEM-CFD). The validation of DEM model, grid sensitivity analysis and heat transfer model are carried out. Based on the above model, the effective thermal conductivity of Li2TiO3 pebble beds with particle size distribution, unitary Li2TiO3 pebble beds and binary Li2TiO3 pebble beds is further simulated and calculated. The influence of particle size distribution, different particle sizes and mixing on the effective thermal conductivity of Li2TiO3 pebble beds is studied. The results show that for the Li2TiO3 pebble beds with similar packing factor, the effective thermal conductivity of Li2TiO3 pebble beds with particle size distribution is similar with unitary Li2TiO3 pebble beds with equivalent particle size. In the case of negligible radiation heat transfer, the effect of particle size on the effective thermal conductivity of unitary pebble bed is negligible. Compared with unitary Li2TiO3 pebble bed, the binary Li2TiO3 pebble bed has higher packing factor and effective thermal conductivity.