Experimental and CPFD study of axial and radial liquid mixing in water-fluidized beds of two solids exhibiting layer inversion

• Axial and radial liquid mixing in a large fluidization column.
• Liquid mixing predictions using CPFD and comparison with experiments.
• Layer inversion effect on liquid mixing.
• Effect of boundary conditions in dispersion models.

Time-responses of concentration of a saline tracer were determined during fluidization by water at 15 °C in a column of 191 mm diameter. Mono-component beds contained 1.85 mm glass beads (density 2500 kg/m3) or 0.550 mm ceramic spheres (density 3800 kg/m3). A binary fluidized bed, containing equal volumes of these two solids, displayed layer-inversion at superficial liquid velocities of 40.5 and 43.5 mm/s at 10 and 20 °C, respectively. Saline tracer pulses were injected just above the distributor, at the column centre. The salt concentration at the bed surface was measured at three radial positions for superficial water velocities up to 127 mm/s. Concentration profiles, simulated by computational particle-fluid dynamics (CPFD) with Eulerian–Lagrangian methodology, showed reasonable agreement with the experimental data. An axial/radial dispersion model was also applied for the mono-component and binary fluidized beds.. The axial dispersion coefficients for the glass beads exceed those for the ceramic spheres. Those for the binary bed are less than expected based on the mono-component data, though a maximum appears at the inversion velocity when closed–closed boundary conditions are employed.