Bubble behavior in a vacuum fluidized bed

Bubble behavior in a vacuum fluidized bed was investigated in this work. Experimental results showed that bubble diameter and rise velocity increased with declining the pressure, whereas bubble density decreased. The evolution of bubble density with bed height could be divided into three stages on the basis of the corresponding net-coalescence rates. The decrease in bubble density in the bottom region accelerated as the pressure decreased, whereas the increase in bubble density in the top region was gentle. Increasing the vacuum degree enlarged the variation in bubble size, resulting in the decline of operating stability in the fluidized bed. A new correlation that considered the effect of operating pressure on bubble behaviors exhibited accurate prediction in the vacuum fluidized bed. Bubble velocity was proportional to bubble diameter for small bubbles, and bed structure obviously affected the rise velocity of large bubbles. The distribution of the bubble aspect ratio was positively skewed and many bubbles had a tendency to become slender as the operating pressure decreased.