鼓泡流化床流动特性的直接颗粒模拟

Direct particle simulation of flow characteristics in bubbling fluidized bed

为了考察流化床中颗粒和气泡运动的基本规律,对两维鼓泡流化床进行了数值模拟.在假设气相为无黏不可压的条件下,求解了体积平均后的欧拉方程,并利用离散单元法(DEM)模拟了颗粒间的碰撞及颗粒与壁面间的碰撞过程.模拟中跟踪了约90000个颗粒,统计了不同床高截面上颗粒及气体纵向平均速度的分布,并对不同表观空气风速和床高下床内压降以及压力波动进行了研究.结果表明,DEM方法能很好地模拟鼓泡床内的流动特性.在床内较低截面上,颗粒及气体的平均速度沿水平方向呈现两个峰,而在较高截面上合并为一个峰.且表观风速越大,气泡运动速度越高.

To investigate the fundamentals of particle and bubble motions in fluidized bed, a two-dimensional bubbling fluidized bed was numerically simulated. The gas phase was assumed as inviscid and incompressible, and the volume-averaged Eulerian equations were solved. The particle-particle and particle-wall collisions were modelled using the discrete element method （DEM）. About 90 000 particles were traced in the simulations, and the vertical mean velocity distributions of particles and gas were statistically calculated at various axial sections of the bed. The pressure drops and fluctuations under various superficial air velocities and bed height were also studied. The results show that the DEM method can better simulate the flow characteristics in the bubbling fluidized bed. The distributions of air and particle mean velocity have two peaks at the lower sections, but are integrated into one at the higher sections. The velocity of the bubbles increases with the increasing superficial air velocity.