Gas-solid Energy-minimization Multi-scale(EMMS) Bubbling Theoretic Model And Its Application

Hydrodynamic modeling of gas-solid bubbling fluidization is of significance to the development of gas-solid bubbling reactors since it still remains at the stage of experimental and empirical science. The energy-minimization multi-scale(EMMS) model enables the quantitative description of gas-solid two-phase flow and is successfully applied to the simulation of gas-solid fast fluidization, because it takes into consideration the meso-scale heterogeneous structure(particle cluster) in gas-solid flow. Gas bubbles in gas-solid bubbling fluidized beds as a typical kind of meso-scale structure, similar to particle clusters in fast fluidized beds, are subject to the constraints of the stability and boundary conditions of the system. Considering this similar physical formation mechanism, this thesis is devoted to extending the EMMS theory further to realize the theoretic modeling of gas-solid bubbling fluidized bed.Firstly, a gas-solid EMMS bubbling theoretic model is developed by considering the expansion work of gas bubbles against the normal pressures stress in the emulsion phase, which can be applied to the steady-state modeling of gas-solid bubbling fluidized beds without introducing bubble-specific empirical correlations such as for diameter. Secondly, the unified modeling of the entire gas-solid fluidization regime from bubbling to fast fluidization is performed by integrating the upgraded gas-solid bubbling model with the original EMMS model, thus laying a basis for the full-loop steady-state modeling of complex gas-solid systems. Thirdly, incorporating the gas-solid bubbling model into commercial computational fluid dynamics(CFD), an effective drag coefficient between gas and solid phases is obtained to account for the effects of the heterogeneous structure and the acceclerations of the gas and the particles. Coupling the above-mentioned drag model with two-fluid model(TFM) by UDF, the unsteady-state simulation of gas-solid bubbling fluidization is realized with a higher accuracy than that based on homogeneous drag models. Finally, based on a simple decomposition of gas-solid complex systems with varying geometries and sizes according to their configuration, a lab-scale circulating fluidized bed with two particle circulation loops is readily modeled by incorporating the gas-solid bubbling theoretical model and the original EMMS model.This work will lay a solid basis for the realization of the EMMS multi-scale computational paradigm featuring with “firstly global calculations, then regional modeling, and finally detailed evolution” as well as so called virtual process engineering(VPE) of chemical engineering, and simultaneously provide quantitative references for the design and scale-up of complex gas-solid two-phase processes.