P revious work in our laboratory has explored several non-intrusive visualization techniques regarding fl ow phenomena in threedimensional, gas-solid fl uidized beds. These methods include X-ray computer assisted tomography (CAT), X-ray Digital Fluoroscopy (DF), and Radioactive Particle Tracking (RPT). X-ray CAT utilizes modifi ed medical CAT scanners to obtain voidage distributions of materials inside a column at varying heights and experimental conditions. X-ray DF employs a medical X-ray camera and an image recording system to obtain information concerning bubble movement, growth, break-up and coalescence in the column. RPT uses gamma cameras to gather instantaneous information regarding radioactive particle count rates and positions in a fl uidized bed over time. These radiation distributions with respect to time are recorded by a computer, and then analyzed to trace the paths of the radioactive particles. The particle paths can lend insight into fl uid behaviour within the column, which could eventually lead to improved design of industrial fl uidized reactors. As a continuation of our previous work in three-dimensional single radioactive particle tracking (Wright et al., 2001), we have developed a method for tracking multiple radioactive particles in three dimensions. Using multiple particles simultaneously allows us to decrease data collection time, decrease the number of images while maximizing the number of points, and obtain overall improved view of fl ow behaviour and particleparticle interactions. This allows us to gather further insight regarding the fl ow structures of three-dimensional fl uidized beds.In this work, we used two gamma cameras, set perpendicular to one another in order to capture the positions and count rates of each of fi ve radioactive particles in three dimensions and as a function of time. The data from each of the cameras was combined to obtain three-dimensional instantaneous particle fl ow information. Particle occurrences, azimuthally averaged velocities, normal and shear stresses and turbulent kinetic energies were found for the data sets.
Experimental EquipmentThe gamma cameras used were a Siemens Orbiter and a Siemens ZLC, each having a 41 cm diameter NaI(Tl) detector crystal and 75 photomultiplier tubes (PMTs). This crystal was covered by a lead LEAP (low energy all purpose) parallel collimator, which allowed only those gamma rays travelling perpendicular to the camera face to pass through. The gamma rays that pass project an image of the radiation distribution inside the column, onto the detector. As gamma radiation is ionizing, the detector crystal produces a fl ash of light, or scintillation event, when struck by gamma rays; scintillation events are proportional