| The gas-solid two-phase flow widely exists in industries such as heat,thermal engineering and chemical industry.Therefore,the study of gas-solid two-phase flow is of great significance to the theoretical models and engineering application.At the same time,the gas-solid two-phase flow exhibits obvious non-uniform structure characteristics under the influence of gas turbulence and gas-solid interaction,which make the flow of discrete particles,particle clusters and bubbles very complicated.The influence of drag force on the gas-solid two-phase flow is dominant in the complex gas-solid two-phase processes.In present study,A dynamic cluster structure dependent(DCSD)drag model is proposed on the basis of the two-fluid model(TFM)and the kinetic theory of granular flow(KTGF).The momentum conservation equation considering the influence of the temporal-spatial characteristics and interaction of particles is established,a multi-scale kinetic energy dissipations equation for heterogeneous gassolid flow considering the collisional interaction of particles is constructed.Compared with the flow characteristics under the Gidaspow drag model,the hydrodynamics characteristics of gas-solid two-phase in risers with different physical parameters are simulated by the DCSD drag coefficient model.The simulation describes the formation and fragmentation of the clusters,predicts the heterogeneous structures characteristics and the core-annular structure characteristics of particle flow in the riser.It was found that the diameter of the cluster was related to the solid concentration.The instantaneous value of convective acceleration is in the same order of magnitude as or 1-2 orders of magnitude larger than the gravity acceleration,the instantaneous value of local acceleration is 1-2 orders of magnitude larger than the convective acceleration,and the time-averaged value of acceleration is roughly in the same order of magnitude as the gravitational acceleration,indicating that the influence of temporal-spatial characteristics of dynamic clusters on the flow characteristics can't be ignored.Through the multi-scale energy dissipation,especially the energy consumption of granular collision,it is found that the energy consumptions of granular collision and drag force affect the formation of the cluster.It shows that the impact of granular collision on the flow characteristics of gas-solid two-phase cannot be ignored.The results show that the simulation results obtained by DCSD drag coefficient model agree better with the experimental data compared with the Gidaspow drag model.A heterogeneous multi-scale dynamic bubble structure dependent(DBSD)drag model which is applicable to the bubbling fluidized bed is constructed on the basis of the flow characteristics of the bubbling fluidized bed and the dynamic cluster structure dependent drag model proposed in this paper.The heterogeneous flow in bubbling fluidized bed is divided into emulsion phase,bubble and the interphase.The momentum conservation equation considering the influence of the temporalspatial characteristics and interaction of particles is established,a multi-scale kinetic energy dissipations equation for heterogeneous gas-solid flow considering the collisional interaction of particles is constructed.The hydrodynamics characteristics in bubbling fluidized bed with different physical parameters are simulated by the DBSD drag coefficient model.The distribution of solid concentration,velocity and bubble in bubbling fluidized bed were studied.From the perspective of the instantaneous value,the value of local acceleration of the bubble is 2 orders of magnitude larger than the value of convective acceleration of the gas.From the perspective of the time-averaged value,the local acceleration of the bubble phase is 2 orders of magnitude larger than the convective acceleration of the bubble phase,the local acceleration of the gas in the emulsion phase is 1 order of magnitude greater than the convective acceleration of the gas in the emulsion phase,the local acceleration of particles in the emulsion phase is in the same order of magnitude as the emulsion phase acceleration particles in the emulsion phase.The multi-scale structure are affected by the granular collision in the bubbling bed with B type particles.In the bubbling bed with A type particles,the drag force energy dissipation plays a leading role in the central region at different heights,the fraction of controlling mechanism of the granular collision near the wall is small,but it is still of influence for the multi-scale parameters of the bubbling bed.It shows that the results of the DBSD drag model agree well with the experimental data.The gas-solid two-phase flow characteristics in CFB are simulated with a kind of horizontal loop seal is put forward.The cross section is changed from the cylinder to the ellipse of different flattening.The flows of particles are predicted by means of discrete element method and kinetic theory of granular flow in the horizontal rotating cylinder drum and horizontal rotating ellipsoidal drum with flattening at different rotation speeds.the characteristics of flow pattern,resulting contact forces,the distribution of velocity,granular temperature,configurational temperature,energy dissipation of the particles in the rotating drum were studied.The results show that the particle flow patterns relate to the rotation speeds and rotating angle of the horizontal rotating ellipsoidal drum,while it is nearly independent of rotating angle of the horizontal rotating cylinder drum.The configurational and translational granular temperatures are larger in the horizontal rotating ellipsoidal drum than those in the horizontal rotating cylinder drum.The mixing of particles is improved at the low rotation speed,and the segregation is enhanced at the high rotation speed in the horizontal rotating ellipsoidal drum as compared to the horizontal rotating cylinder drum.The CFB with a kind of horizontal screw loop seal is simulated.The results show that the solids circulation flow rate increases with the increase of rotating speed,and the solids circulation flow rate could be controlled by adjusting the rotating speed of screw loop seal. |
PDF Full Text Request