Longitudinal mixing in fluidization

Longitudinal mixing properties in liquid-solid fluidized beds were investigated by means of a salt-solution tracer technique. The electrical conductance breakthrough curves were measured with very small electrical conductivity probes for a step-function input of salt-solution tracer. Longitudinal eddy diffusivities were determined for 1.3- and 3.0-mm. lead spheres and 3.2-mm. glass spheres in 2- and 4-in.–diameter beds at a distance of 5 bed diam. from the injector and for various radial positions. The longitudinal mixing properties are strongly affected by particle concentration; maximum mixing occurs at a fraction voids of 0.7. Longitudinal eddy diffusivity increases with particle density and with decreasing dp/D ratio. Velocity profiles markedly influence the eddy-diffusivity profiles.