Modeling of Bubble-Structure-Dependent Drag for Bubbling Fluidized Beds

Considering the effect of bubble-emulsion structures in bubbling fluidized beds, a bubble-structure-dependent drag coefficient model is developed. Accelerations in the bubble and emulsion phases are incorporated into the solution of the drag coefficient. Meanwhile, the influence of solid pressure and bubble-induced added mass force is also taken into account. In combination with the two-fluid model, flow behaviors in two-dimensional and three-dimensional bubbling fluidized beds are simulated. The predictions by the present model with consideration of bubble effects are in more reasonable agreement with the experimental results compared to the Gidaspow drag model. It is shown that the present model obtains a zonal distribution of the drag coefficient with solid concentration, which reveals that the drag coefficient not only depends on the local solid concentration but also is greatly influenced by the local velocities.