Investigation Of Gas-Solid Two-Phase Flow Behavior In Fluidized Bed By Means Of Les-Dsmc Method

Gas-solid two-phase flow is widely existed in the industrial processes. Numerical simulation has become one of the most important methods to investigate gas-solid two-phase flow because of its unique advantage. Recently, discrete particle model in which particles are directly tracked was paid widely attention due to the great development of computer hardware. In this model, gas phase is treated as continuous medium, and particle phase is treated as the discrete system. Because particle movement is investigated in the particle-level, the multi-scales structure of fluidized bed can be simulated in both particle-scale and macro-scale.Discrete particle models can be classified into Deterministic method and Stochastic method in accounting for the particle collisions. In the previous direct simulation Monte Carlo (DSMC) method used in the dilute gas-solid flow, particle collision probability was calculated by the equation used for rarefied gas molecules. And gas phase was simulated by the laminar Navier-Stokes equations. However, the effect of high particle concentration on particle collision should be taken into account in the dense gas-solid two-phase flow. At the same time, gas turbulence should be taken into account in the simulation of gas flow in dense gas-solid two-phase flow.A discrete particle motion-collision decoupled model was established in which particle collision was modeled by means of DSMC method. The radial distribution function was introduced in order to take into account the effect of the uneven local particle concentration on the particle collision probability. The large eddy simulation (LES) was used to model gas turbulence. The sub-cell technology was applied to save computational time and improve the rationality of sampling collision partner.Numerical simulations of flow behavior of particles and clusters were performed in a circulating fluidized bed by means of the LES-DSMC methods. The distributions of time-averaged particle velocity and concentration were obtained. The instantaneous particle positions and velocities, and the concentration of particles located in the cell as a function of time were analyzed. The effects of superficial gas velocities and restitution coefficients on the flow behavior of two-phase flow and clusters were analyzed. The particle collision frequencies and granular temperature as a function of particle concentration were obtained. The duration time, averaged...