Studying the effect of hydrodynamic parameters on characteristics of the gas bubbles in tapered fluidized beds

The two-fluid model is applied to explore the effects of various parameters including initial static bed height, superficial gas velocity, and a mixture of particles of different sizes and densities on the size distribution and rise velocity of gas bubbles in tapered fluidized beds. Comparison of simulation outcomes with experimental data about the fraction and rise velocity of bubbles is carried out and relatively good agreement is observed. Results indicate that increasing static height of the solid leads to increased bubble fraction and rise velocity. The fraction of medium and large bubbles has direct relationship with the superficial gas velocity but that is reverse for the bubbles with small diameters. For a solid mixture with different sizes or densities, the bubble fraction goes up with an increase in the percentage of lighter solid from 25 to 50%, but it drops as the percentage increases from 50 to 75%. At lower bed heights, bubble rising velocity decreases with an increase of the portion of smaller particles in a solid mixture. The rise velocity of bubbles is ascending with inlet velocity of the gas phase.