effect of bed diameter on the hydrodynamics of gas-solid fluidized beds

effect of scale on the hydrodynamics of gas-solid fluidized beds was investigated in two fluidized beds of 152 mm and 78 mm in diameter.  air at room temperature was used as the fluidizing gas in the bed of sand particles. the radioactive particle tracking (rpt) technique was employed to obtain the instantaneous positions of the particles at every 20 ms of the experiments. these data were used to calculate hydrodynamic parameters, such as mean velocity of upward and downward-moving particles, jump frequency, cycle frequency and axial and radial diffusivities, which are representative of solid mixing and diffusion of particles in the bed.  these hydrodynamic parameters were compared in both scales in order to determine the scale effect on the hydrodynamics of the gas-solid fluidized bed.  in all cases, it was shown that solid mixing and diffusivity of particles increase by increasing column diameter.  the results of this study would help to understand solid mixing which might be critical in industrial fluidized bed reactors.