The EMMS Drag Force Model For Discrete Particle Method And Its Application

Gas-solid fluidized bed is widely used in the process industry.The flow field inside gas-solid fluidized bed is a typical non-equilibrium and inhomogeneous system,where there exists mesoscale structures e.g.particle clusters.Those make it difficult to the simulation of gas-solid fluidized bed.In gas-solid two-phase flow systems,the drag force plays an important role in the evolution of the flow field.Therefore,it is necessary to establish an inhomogeneous drag model which can describe the mesoscale structure.Most of the inhomogeneous drag models were developed based on the two-fluid model,while there is seldom report about the inhomogeneous drag model for discrete particle method.In this study,we investigate the discrete-based inhomogeneous drag model(EMMS/DP)in the framework of the energy minimization multi-scale(EMMS)theory and simulate several gas-solid fluidized bed risers with the EMMS/DP drag model.Finally,this method has been used in the prediction of gas-solid flow behavior in cold-state HT-L gasifier.The content of each chapter of this dissertation is as follows:Chapter 1 summarizes the development of the gas-solid fluidization system.Three currently popular numerical simulation methods are introduced in this chapter,and the development process of heterogeneous drag model is made a brief introduction.Finally,we propose the necessity of developing the inhomogeneous drag model for discrete particle method.In chapter 2,we introduce the MP-PIC method which is a coarse grained numerical simulation method belonging to the particle tracking model used in this dissertation.Two risers are simulated by this method and the simulation results are in good agreement with the experimental measurements.Two important parameters of this method:grid resolution and coarse graining parameters were discussed in this chapter.In chapter 3,the EMMS drag model for discrete particle method(EMMS/DP)was improved and developed.This study improves the generating method of particles information and correlates the heterogeneity index(HD)with solid concentration and slip velocity to account for the dynamic effects of meso-scale structure.Further we developed this drag model by introducing the influence of operating conditions on the mesoscale structure so that it can adapt to a variety of operating conditions.Then,different gas-solid fluidized bed risers and different operating conditions were simulated with the improved drag model.The simulation results agreed well with the experimental work.In chapter 4,the experimental device of HT-L gasifier was simulated by using the improved drag model.The simulation results can capture the phenomena of particle agglomeration and backmixing.The overall reproduction of the flow field is consistent with the experimental measurement.In chapter 5,we summarize this dissertation and provide suggestions for future work.