Numerical Investigation Of The Flow Behavior Of Dense Granular Materials

Dense granular materials are widely encountered in various industrial processes.Thorough understanding of the complex flow behavior of dense granular materials is thus critical for the design,optimization and scale-up of relevant equipments.Focusing on moving bed and spouted bed systems,in this work the flow characteristics of dense granular are numerically investigated and the suitability and predictive ability of several constitutive laws for granular material are evaluated.In order to provide the basic data for quantitative evaluations of the correctness of continuum simulations,in chapter 2 the discharging behaviors of granular materials from moving bed are simulated using Discrete Element Method(DEM).It is found that,with the increase of initial packing height,the flow structure switches from type C funnel flow pattern to type B semi-mass flow pattern.For funnel flow pattern,there exists a smooth transition of(expansion)-saturation-shrinkage of flowing zone during the whole discharge process.As to semi-mass flow structure,the flow pattern quickly switches into funnel flow pattern when the sample height is smaller than a critical value.After that,the characteristic width of the flowing zone decreases monotonously with the ongoing of discharge.Such results indicate that during silo discharge,the flowing zone width is closely related to the discharging history.In chapter 3,the predictive abilities of three commonly used frictional viscosity models(Schaeffer,S-S,?(?))in simulating silo discharge are assessed.It is found that,for systems with initial flow structure being funnel flow,both Schaeffer model and ?(?)model can successfully give the correct flow pattern.However,the predicted variation trend and their quantitative values of the characteristic width of flowing zone clearly deviate from the DEM results.As to systems with initial flow structure being semi-mass flow,Schaeffer model and ?(?)model can correctly predict the flow structure switching from type C to type B.And the obtained characteristic widths of flowing zone are in good agreement with the DEM results.For all the considered initial packing heights,the continuum simulations using S-S model always predict the formation of semi-mass flow,which clearly deviates from the DEM results.To further evaluate the predictive abilities of the considered three frictional viscosity models,in chapter 4 the hydrodynamic characteristics of gas-solid spouted bed are modeled.It is found that the fountain height,voidage and the geometrical shape of spouting region predicted by ?(?)model are very close to the experimental results.The pressure drop given by Schaeffer model is in better agreement with the experimental datum.In fountain region and spouting region,the simulation results predicted by the three model are very close to each other.Nevertheless,in the annulus region the simulation results given by ?(?)model are more close to experimental data.In brief summary,compared with Schaeffer model and S-S model,?(?)is more suitable for modeling the hydrodynamic behavior of gas-solid spouted bed.