Multi-scale simulation on hydrodynamic characteristics in bubbling fluidized bed

Bubbling fluidized beds have been widely applied to various industrial processes owing to superior inter-phase contact and high heat transfer characteristics. Fundamental knowledge of the hydrodynamic characteristics is essential for the design of such reactors. In bubbling fluidized bed systems, the non-uniform flow structure in the form of bubbleemulsion phases makes the accuracy of numerical model limited. Bubbles are the typical meso-scale structures in bubbling fluidized beds. To describe the effects of such meso-scale structures, a bubble structure-dependent (BSD) drag model is developed with one extremum condition of energy dissipation consumed by the drag force, which is incorporated into the two fluid model. The simulations of gas-solid flow behavior in bubbling fluidized beds with with Geldart A and B particles are performed and some parameters including bubble velocity and bubble diameter are analyzed. The results indicate that the present model with consideration of bubble effects obtains a zonal distribution of the drag coefficient with solid concentration, which establishes a relationship between the drag coefficient and the local structural parameters. Comparisons with experimental data, the BSD drag model can obtain a better prediction than the conventional drag model. Meanwhile, the simulation reveals that the BSD drag model has a more significant impact on the predition of bubbling fluidization with Geldart A particles.