Random Particle Size Fluidized Bed Lagrangian Simulation

In the engineering, particle diameters are obeyed some distribution rules in gas-solid fluidized beds, but which isn't obeyed in previous studies. Based on the particle-motion-resolved discrete model, a soft-sphere method and a hard-sphere method used for the simulation of fluidization are established in which particle diameters obeyed random distribution. In our model, the particles motion is dominated by using the Newton's second law, and fluid motion is described by the Navier-Stokes equation, the interaction between two-phase is treated by the third Newtonian theory. Dynamic behaviors in the gas-solid fluidized beds are simulated for three parts.Firstly, a soft-sphere method used for the simulation of fluidization is established in which particle diameters are obeyed random distribution. The above-mentioned model has been used for simulating bubbling and slugging behaviors in the fluidized beds. Then the distributive rules of solid velocities are studied when gas superficial velocities, stiffness and distributions of particle diameters are different. Simulation results indicate that the structure of distributor and gas superficial velocity have some influences on the bubbling phenomena, and the formation, rise and break of bubbles are accelerated with increasing the gas superficial velocity. The bigger the stiffness is, the quicker the axial solid velocities decays with increasing time. At the same time, the axial solid velocities of wide distribution for different particle diameters are bigger than that of narrow distribution.Secondly, a hard-sphere method used for the simulation of fluidization is established in which particle diameters are obeyed random distribution. At the same time, the searching strategy of particle collision is also improved. The above-mentioned method has been used for simulating bubbling and slugging behaviors in the fluidized beds. And the distributive rules of solid velocities are studied when distributions of particle diameters are different. Simulation resultsindicate that the structure of distributor has distinct influences on the bubbling behaviors. Moreover, the axial solid velocities of wide distribution for different particle diameters are bigger than that of narrow distribution.Thirdly, in order to compare the difference between hard-sphere method and soft-sphere method, the dynamic behaviors in gas-solid fluidized beds are simulated by hard-sphere method and soft-sphere method in which particle diameters are obeyed random distribution. And particle average velocities with increasing time and particle trajectories are compared. At the same time, the dynamic behaviors in fluidized beds and the distributive rules of particle average velocity are also studied when restitution coefficients are different. Simulation results indicate that restitution coefficients of hard-sphere method and soft-sphere method have distinct influence on particle average velocities. The bubbling phenomena can be simulated by hard-sphere method when restitution coefficients are smaller, while it can be simulated by soft-sphere method when restitution coefficients are bigger. The bigger restitution coefficients are, the larger are the change of particle average velocities in hard-sphere method, but the smaller are the change of particle average velocities in soft-sphere method. Moreover, the CPU time in hard-sphere method is much bigger than that of soft-sphere method due to the different ways in dealing with the collisions and the different time step of particle collisions.