流化床中动态行为硬球模拟与软球模拟的比较

Comparison of dynamic behavior between hard-sphere andsoft-sphere simulation in gas-solid fluidized beds

用硬球方法和软球方法分别模拟了不等粒径流化床中的动态行为;比较了颗粒平均速度、运动轨迹的差异;研究了恢复系数对流化床中动态行为、颗粒平均速度的影响.研究结果表明对流化床中动态行为进行模拟的数值结果强烈地依赖于恢复系数,恢复系数较小时,硬球方法可以模拟出鼓泡现象,恢复系数较大时,软球方法可以模拟出鼓泡现象;并且恢复系数越大时,硬球方法中颗粒平均速度随时间的变化越大,而软球方法中颗粒平均速度随时间的变化越小;尽管硬球方法比软球方法更加准确地考虑了颗粒碰撞,但由于硬球方法和软球方法处理颗粒碰撞方式的不同,以及颗粒碰撞时间步长选取原则的差异,使得硬球模拟需要的计算时间远大于软球模拟需要的计算时间.

In order to compare the difference between the bard-sphere method and soft-sphere method, the dynamic behavior in gas-solid fluidized beds was simulated by the hard-sphere method and soft-sphere method in which particle diameters were unequal. Particle average velocities with increasing time and particle trajectories were compared. At the same time, the dynamic behavior in fluidized beds and the distribution of particle average velocity were also studied when restitution coefficients were different. Simulation results indicated that restitution coefficients of the hard-sphere method and soft-sphere method had distinct influence on particle average velocities. The bubbling phenomena could be simulated by the hard-sphere method when restitution coefficients were smaller, while such phenomena could be simulated by the soft-sphere method when restitution coefficients were larger. The larger restitution coefficients, the larger the change of particle average velocities in the hard-sphere method, but the smaller the change of particle average velocities in the soft sphere method. Moreover, the CPU time in the hard-sphere method was much larger than that of the soft sphere method due to the different ways in dealing with the collisions and the different time steps of particle collisions.