Parallel CFD-DEM Simulation Of Flow Characteristics In A Three-dimensional Spout Bed

The fluidized bed has the characteristics of particle circulation, particle contact heat transfer, mass transfer and so on. It is widely used in industrial fields, such as coating, granulation, combustion, desulfurization and other chemical reactions. The concentration field, velocity distribution and the number of collisions between particles and walls are of great significance for the design and optimization of industrial production. Numerical simulation has become an important method to study the characteristics of gas-solid two phase flow.Computational fluid dynamics(CFD)- discrete element method(DEM) is widely used in numerical simulation of fluidized bed, but it is difficult to meet the requirements of the simulation of the actual fluidized bed. Therefore, it is important to study the DEM parallel algorithm. Firstly, according to the characteristics of particle motion in the fluidized bed, parallel computing model of particle-phase in gas solid two-phase flow based on the method of DEM is established, which can achie ve the parallelization for force calculation of particles, update for velocity and location of particles on the basis of the OpenMP parallel technology, a 3D parallel DEM code for simulating the particle deposited process in a fluidized bed is developed based on the OpenMP standard in this paper. Compared with the serial one, the results of parallel program show that it has a better speedup than the serial program, and the computational efficiency is improved greatly with the parallel program. With the number of threads increasing, the speedup increased gradually, while the increase rate is relatively reduced.Secondly, a three-dimensional gas-solid flow CFD-DEM program is compiled with the parallel algorithm, which obtained flow process diagram under different spouting velocity and the velocity distribution of gas and particles, and the axial and radial distribution of particle volume fraction by simulation. What's more, the simulation results were analyzed : driven by the air jet in the bed center, the particle generated core annulus flow, and the stagnation zone appear in both sides of the bottom of the bed; When the spouting velocity increase, the ability of gas entraining particles enhanced, which resulted in the area of the stagnation zone decreased relatively. Meanwhile, the volume fraction of the particles decreased when the spouting velocity increased, and the voidage in the bed increased, the liquidity of particles enhanced relatively.Lastly, mixing mechanism of the axial and radial direction and the effect of the spray velocity on the mixing of the particles in the bed were quantitatively analyzed by the introduction of Lacey stochastic mixture index. In axial of the bed, the particle mixing mainly through the transposition, while in the radia l, the particles mixed by random. Besides the axial mixed rate was faster than the radial one, the increasing of superficial gas velocity caused the axial and radial mixing speed increas ing.