Micromechanical analysis of bubbles formed in fluidized beds operated with a continuous single jet

Abstract

Advancement in the knowledge of bubble dynamics and properties can significantly aid to improve the design and operation of gas-solid fluidized beds. In this work, bubble properties in a single jet fluidized bed were studied by the combined approach of CFD and DEM. The results illustrated that the process of the continuous injection of a central air jet to the bed was successfully reproduced, with the formation of a series of bubbles which rise through the bed and burst at the bed top. During this process, the series of bubbles align vertically which show coalescence in three different levels of the bed. However, the coalescence patterns depend upon jet velocity and are fairly regular. The bubbles are categorized into two types: primary/leading bubbles and trailing bubbles. The size of primary bubbles keeps increasing with bed height while the size of trailing bubbles decreases since trailing bubbles coalesce with primary bubbles. Primary bubbles, although formed at different times, are of similar shape at different heights of the bed while trailing bubbles are generally elongated in shape. Trailing bubbles have a higher velocity than primary bubbles. The spatial analysis of pressure gradient, drag, and particle-fluid interaction force shows that the presence of bubbles leads to different particle flow zones where forces vary significantly. Moreover, the bubble passage can be delineated by the temporal variation of the particle-fluid interaction force.