Cloud formation around bubbles in gas fluidized beds

Gas flow through a fluidized bed is normally streamline and the pattern of flow depends on the bubbles within the bed and their velocities relative to gas. When the gas velocity for fluidization is low compared with the bubble velocity (as in beds of fine particles) a region of gas circulation or a "cloud" as it is called, is formed around the bubble.

This paper describes experimental observations of the shape and size of gas clouds as they form around bubbles in two-dimensional fluidized beds of spherical and irregular particles. Exchange of gas between the cloud and interstitial phases is shown to occur by a process of "cloud shedding," and the behaviour of clouds as their parent bubbles split and coalesce is described. The observations of cloud shape are compared with the theoretical predictions of DAVIDSON, JACKSON and MURRAY and from this an estimate of the cloud shape in real three-dimensional beds is made.