Visualization of bed material movement in a simulated fluidized bed heat exchanger by neutron radiography

The bulk movement of fluidized bed material was visualized by neutron radiography by introducing tracers into the bed materials. The simulated fluidized bed consisted of aluminum plates, and the bed material was sand of 99.7% SiO2 (mean diameter: 0.218 mm, density: 2555 kg/m3). Both materials were almost transparent to neutrons. Then the sand was colored by the contamination of the sand coated by CdSO4. Tracer particles of about 2 mm diameter were made by the B4C, bonded by the vinyl resin. The tracer was about ten times as large as the particle of fluidized bed material, but the traceability was enough to observe the bed-material bulk movement owing to the large effective viscosity of the fluidized bed. The visualized images indicated that the bubbles and/or wakes were important mechanism of the behavior of the fluidized bed movement.