Flow structure in a three‐dimensional bubble column and three‐phase fluidized bed

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Abstract
Macroscopic flow structures of 3‐D bubble columns and gas‐liquid‐solid fluidization systems under various operating conditions are studied using particle image velocimetry. Flow visualization is also conducted with the aid of a laser sheeting technique. The refractive index matching technique is used to eliminate the opaqueness of solid particles occurred in the visualization study of gas‐liquid‐solid fluidization. Three flow regimes (dispersed bubble, vortical‐spiral flow, and turbulent flow) are identified. The flow structure is investigated for various operating variables including liquid velocity, gas velocity, and particle holdups. Four flow regions (descending flow, vortical‐spiral flow, fast bubble flow, and central plume) can generally be characterized in the vortical‐spiral flow regime where the gross circulation pattern occurs. A conceptual model for the flow structure in the vortical‐spiral flow regime is discussed. The transition of the flow regimes and structure in the vortical‐spiral flow regime is postulated to be related to the Taylor instability for flow between two concentric rotating cylinders. Similarities between the flow structures of 2‐ and 3‐D beds are also discussed.