基于聚团-力平衡修正模型的粘性颗粒流动特性的CFD模拟

CFD Simulation on Fluidization Behavior of Cohesive Particles Using Modified Agglomerate-Force Balance Model

建立了基于粘性颗粒鼓泡流化床中气泡直径得到聚团相对运动速度,进而计算聚团尺寸的方法,对周涛的原聚团-力平衡模型进行了有效的修正,并对修正模型的正确性进行了验证。采用了基于聚团-力平衡修正模型对粘性颗粒的流化状态进行了三维模拟。不同气速下固含率的计算结果与实验数据基本吻合,但由于该模型未能很好地体现颗粒在床层顶部的返混情况,使得顶部固含率的计算值和实验值之间存在一定的偏差。计算得到的聚团尺寸随着所处床层高度或气速的增加而逐渐减小。正如实验现象所观察到的,通过对颗粒聚团运动速度的矢量分析验证了固相从床层中心和边壁下落、从两侧上升的双循环结构。

The original Zhou Tao’s agglomerate-force balance model was modified with the bubble size of the fluidized beds with cohesive particles. The computational fluid dynamics （CFD） simulations of gas and cohesive solids flows were carried out using the modified agglomerate-force balance model in two and three dimensional conditions, respectively. The simulated results agreed approximately with experimental data, while a few discrepancies existing at the top of bed were due to that the present model did not take the back-mixing effect into account. The computed agglomerates sizes decreased with increasing of bed height or gas velocity, and the cross-sectional distribution of solids axial velocity and solids holdup were found to be just contrary to each other. According to the velocity vectors of agglomerates, the solid particles in the center and wall fell down, while the particles in both sides rose up, and two core-annular flows existed in the bed, which could be also observed experimentally.