Voidage characteristics and prediction of bed expansion in liquid-solid inverse fluidized bed
Studies on voidage fluctuations, axial voidage profile and bed expansion are carried out by measuring the local void fraction using particles of wide ranging characteristics in liquid-solid inverse fluidized bed. The quality of fluidization is elucidated by the local voidage fluctuations. The RMS voidage fluctuation depicts a maximum with respect to average bed void fraction and increases with increase in Archimedes number. The fluidization quality has been quantified using average normalized RMS voidage fluctuation in terms of Transition number. The axial void fraction is almost uniform throughout the bed except for particles with size distribution. All the literature and present experimental data on bed expansion are unified in terms of Richardson and Zaki equation using experimental terminal velocities. A new correlation is proposed for predicting the wall effect corrected experimental terminal velocities, as a substitute for standard drag equation. The bed expansion data are also predicted using the drift flux model. © 2005 Elsevier Ltd. All rights reserved.
Spatio-temporal evolution of void fraction in liquid-solid inverse fluidized bed
Experiments were conducted to investigate the unsteady state void fraction characteristics of inverse fluidized bed (IFB) subjected to step change in liquid velocity. The resulting temporal and spatial evolution of void fraction in IFB is studied for the first time in the literature. The experimental profiles could be explained by the existing theories. The particle bed model proposed by Foscolo and Gibilaro [1987. Fluid dynamic stability of fluidized suspensions: the particle bed model. Chemical Engineering Science 42(6), 1489-1500.] is used to predict the experimental spatio-temporal variation of void fraction, and the time history of bed surface and voidage interface. In general, a good agreement is obtained between the experimental results and model prediction. The hyteresis phenomenon occurring during unsteady state conditions is also explained. © 2006 Elsevier Ltd. All rights reserved.