Mesoscale Simulation of Bubble Behavior in Bubbling Fluidized Beds

Bubbles are typical mesoscale structures in gas-solid bubbling beds. The behavior of bubbles play a key role in gas-solid mass and momentum transfer. To accurately describe the bubble structure and its dynamic changes caused by complex gas-solid interactions, it is worth exploring the mesoscale model and conducting simulation studies. The lattice gas cellular automata (LGCA) model is a numerical simulation method from a mesoscopic view. The core of the LGCA model is to describe the complex macroscopic phenomena based on the microscopic or mesoscopic self-organized evolution according to specific model evolution rules. It features the simplicity in algorithms and the capability of dealing with complex boundaries.

Based on our previously proposed LGCA discrete mesoscale model for gas-solid two-phase flow (Zheng et al., 2011), the model evolution rules were revised for forces including particle gravity and bubble surface tension, and gas-solid interactions. In this paper, by analyzing the characteristics of the bubbles in fluidized beds, specific set of evolution rules were further defined corresponding to the local hydrodynamic properties, i.e. bed height, pressure, voidage, and particle velocities. With this set, a certain set of evolution rules was activated when the corresponding local hydrodynamic state is identified.

The model is then validated by simulating the formation, growth and collapsing of bubbles in the two-dimensional bubbling bed. The comparison between the simulation and the experimental characteristics of the corresponding cold model shows that the proposed self-organizing evolution mechanism of this LGCA model is capable of describing the macroscopic bubble behavior in the gas-solid bubbling fluidized beds.