Effects of pressure and particle size on bubble behaviors in a pseudo 2D pressured fluidized bed with Geldart A/B, B and D particles

Bubble behaviors of three types of particles from Geldart A/B, B and D groups were comprehensively investigated in a pseudo 2D pressurized fluidized bed via digital image analysis. Based on the analysis of a large quantity of experimental data, the effects of pressure and particle size on the spatial distribution of bubbles, bubble diameter, rise velocity, bubble fraction and flow regimes were obtained. Results show that bubbles are smaller and uniformly dispersed throughout the bed of Geldart A/B particles, while they become densely populated and grow into much larger sizes in the bed of Geldart B particles. A single peak of large bubbles in the center and emptying of bubble near the walls is formed in the bed of Geldart D particles due to the preferable rising path of bubbles towards the center and the significant coalescence of bubbles. Bubble diameter decreases with increasing pressure, and the effect of pressure is more pronounced on Geldart D particles. Bubble rise velocity increases with the increasing particle size and decreases as pressure rises. Large bubbles/slugs hardly appear in the bed of Geldart A/B particles, while they are clearly visible in the bed of Geldart B and D particles. The flow regime transition from slugging to fast fluidization shifts to the lower gas velocity for Geldart D particles compared with Geldart B particles.