Characteristics Of Flow Behavior In A Liquid-solid Fluidized Bed Using Anisotropic Second-Order Moments Model

The mechanisms and characteristics of liquid-solid two-phase flow is an important issue in petroleum or chemistry industry.It is worthy to predict and utilize some unique characteristics in liquid-solid fluidized bed,such as mixing and mass or heat transfer,which can be benefit to understand industrial process.To date,lots of studies are concentrating on isotropic assumption regarding particle flow,however,the de facto particle flow in liquid-solid fluidized bed usually shows obvious anisotropic behavior.Therefore,it is necessary to develop and improve a more reasonable kinetic model taken anisotropic phenomenon into account.The foundation of this dissertation derives from the kinetic theory of dense granular flow,which is used to establish transport equation for the second-order moments of particle fluctuating velocity.Also,the constitutive model for solid phase is closed by above mentioned kinetic method.In addition,with the combination between kinetic theory and particle-wall collisional restitution coefficients in normal and tangential component,the boundary condition of particle velocity and second-order moments can be smoothly obtained.Based on the Razzak experiment about liquid-solid riser,simulations are adopted in two ways,kinetic theory of granular flow model(KTGF)and second-order moments model(SOM),respectively,to analyze and compare flow characteristics.Simulated results from second-order moments model can be better in agreement with original experimental data,comparing to the kinetic theory of granular flow model.Additional,the component of second-order moments in the axial direction is higher than that in the radical direction.The axial particle velocity will gradually increase with increasing inlet liquid velocity.Hence,collisions among surrounding particles and interactions between liquid and solid phase are two main contributors that the dissipation of the particle fluctuating energy coincides with fluidized process.Moreover,the granular temperature increases to a maximum critical value,and then gradually decreases with increasing solid volume fraction.With the purpose of verifying the accuracy of the second-order moments model in broader applications,the downcomer from Lan experiment is also conducted in flowing simulations.The simulated results show strong antistrophic behavior of particle flow in three regions—freeboard,dilute area and dense area—from this downcomer.Besides,if the area that particle volume fractions are pretty high exists in lower height,the simulated results from the kinetic theory of granular flow model,which regards the particle flow as isotropy,could be closer to original experimental results comparing to that applied in dilute area.In conclusion,the second-order moments model(SOM)is an advantageous model to numerical simulate the liquid-solid two-phase flow.