Macroscopic mixing in fluidization

Mixing studies were performed in beds of lead and glass particles fluidized with water. A salt solution was injected from a point source, and electrical conductivity cells were used to determine time average and fluctuating salt concentrations at various points downstream from the point of injection. The frequency distribution of the fluctuations was determined, and correlation coefficients were measured for the fluctuations at two points separated by a known distance. The mixing data for the central portion of the bed yield radial eddy diffusivities and scales and intensities of turbulence. At the same fraction void the eddy diffusivity and scale of turbulence are larger for lead than for glass particles, but the velocity fluctuations appear to be independent of the density of the particles. Minimum Peclet numbers are observed at a fraction void of about 0.7. Scales based on correlation coefficients exceed those calculated from Peclet numbers, indicating that in a fluidized bed there are large-scale eddies whose size is much larger than a particle diameter. The interpretation of the mixing data is coupled with visual observations of fluidized bed flow patterns.