Experimental measurements of gas pressure drop of packed pebble beds

Abstract

The nearly spherical shaped ceramic pebble beds in the breeder blanket of the future fusion reactor are purged by low-pressure gas to channelize the produced tritium fuel into the tritium extraction system. The required pumping power for the flowing gas in pebble beds can be estimated using the pressure drop across the pebble beds. The aim of this work is to measure the gas pressure drop experimentally across packed pebble beds as a function of pebble sizes, pebble shapes, pebble materials, and gas velocity. The pebble beds are packed in a cylindrical-shaped stainless steel container with an inner diameter of 24 mm and a length of 130 mm. The various experiments have been performed on stainless steel spheres (Diameter: 1 mm, 2 mm, 3 mm, and 4 mm), alumina pebbles (Mean diameter: 1 mm and 1.5 mm), and lithium meta-titanate pebbles (Mean diameter: 1 mm and 1.3 mm). The gas flow has been controlled and measured using a digital mass flow controller. The static differential pressure across the pebble beds has been monitored by a differential pressure transducer. The pressure drop significantly increases with a decrease in the diameter of pebbles/spheres and an increase in the packing fraction of the bed. The material type does not affect the results which are too obvious for the fixed pebble bed which is considered in these experiments. The obtained experimental results of gas pressure drop have been compared and agreed well with the prediction of the Ergun’s correlation.