Effects of Pressure and Fines Content On Bubble Diameter in a Fluidized Bed Studied Using Fast X-Ray Tomography

Using a fast X-ray tomography setup the bubble size and velocity has been measured in a 25 cm diameter fluidized bed of Geldart B powder and a 24 cm bed of Geldart A powder. The average bubble size has been determined for a measurement period of 60 seconds. The resolution of this setup is about 4.5 mm per pixel at a rate of 250 reconstructions per second. It is possible to detect bubbles as small as 2.2 cm. The Geldart B powder consisted of polystyrene particles with an average diameter of 607 mm and a bulk density of 625 kg/m³. This bed was studied at pressures ranging from 1 to 5 bar. The superficial gas velocities varied from 12 to 32 cm/s for the atmospheric pressure measurements; for the highest pressure from 10 to 15 cm/s. The bubble size is significantly reduced at higher pressures for similar gas flows. The Geldart A powder consist of a base of aluminum oxide particles with an average diameter of 76 mm and a bulk density of 680 kg/ m³. Varying amounts of fines were added to these base particles. The fines consist of aluminum oxide particles with an average diameter of 38 mm and a bulk density of 620 kg/ m³. An increase in the fines content from 0 to 50% _weight leads to a decrease in the average spherical equivalent bubble diameter by 20%.