Measuring and modeling solids movement in a large, cold fluidized bed test facility. Third quarterly report, April 1-June 30, 1980

A considerable fraction of the apparent gas dispersion coefficient of a fluidized bed is due to a non-dispersive meander of the bed gas as it travels up through the bed. The experimental results indicate that a dispersion coefficient which is obtained by measuring the time average concentration at some location in the bed and then comparing the concentration to the tracer inlet rate will overestimate the real turbulent/molecular dispersion coefficient by as much as 60 to 70%. The meander coefficient was observed to vary from 0.0005 ft/sup 2//sec at a superficial velocity of 1.5 ft/sec (about 1.9 u/sub 0//u/sub mf/) to about 0.068 ft/sup 2//sec at an air velocity of 6.0 ft/sec. The corresponding range in the turbulent/molecular dispersion coefficient was 0.004 ft/sup 2//sec to 0.10 ft/sup 2//sec. The meander coefficient shows a continued increase with air velocity whereas the turbulent/molecular coefficient was very close to the same value for the two highest velocities. There is some weak evidence of anisotropy in the meander dispersion coefficient. The turbulent/molecular coefficient seems to be independent of location