Dispersion of tracer gas supplied at the distributor of freely bubbling fluidised beds

Abstract

The dispersion of tracer gas, continuously injected beneath an isolated area of the distributor plate, has been determined from time averaged concentration measurements in freely bubbling three dimensional air fluidised beds. The concentration profiles at different levels and for a series of flow rates have been plotted dimensionlessly showing them to be substantially alike in shape, this plot has been well fitted with a simple expression [1]. The tracer dispersion at points within the bed has been successfully predicted using a single phase model, depending mainly on the radial dispersion coefficient. The radial dispersion coefficient has been found to be roughly constant at all levels in the bed (except near the bottom where it is high), but increases rapidly, from a value near molecular diffusion, with an increase in the excess gas flow ( U — U m.f.). Within the experimental range considered, it appears that the Peclet number is inversely proportional to the average bubble diameter.