颗粒数方程的求解及流化床数值模拟

Solution of Population Balance Equation and Numerical Simulation of Fluidized Bed

流化床内颗粒聚并和破碎将影响颗粒相的流动特性.本文运用基于颗粒动理学理论的欧拉一欧拉气固多相流模型,利用直接矩积分方法求解颗粒数平衡方程,建立颗粒数密度与连续性方程、动量方程之间的关系,数值模拟流化床内两种不同直径颗粒发生聚并时气固两相流动特性。计算结果表明,颗粒聚并伴随着床内颗粒直径逐渐增大,床内颗粒流化状态逐渐变为固定床状态,两种颗粒直径均增加,且小颗粒的体积分数逐渐减小、大颗粒的体积分数增加。当仅考虑聚并过程时增加流化速度将导致床内颗粒体积平均直径变大。随着颗粒密度减小,床内体积平均直径增加。

Aggregation and breakage of particles occurred in the gas-solid fluidized bed influence the flow behavior of solid phase.In this paper,an Euler-Euler two flow model is used on the basis of the kinetic theory of granular flow.The population balance equation of particles(PBE) is solved by means of Direct Quadrature Method of Moments(DQMOM) and coupled to the continuity and momentum balance equations.Flow behavior of solid and gas phase has been numerical simulated in a fluidized bed.The results show that the diameter of agglomerated particle will increase due to the aggregation of particles.A fully fluidized bed becomes gradually to a fixed bed because of particles agglomeration.The diameter of agglomerated particles increases,and the volume fraction of small particles reduces in the bed.At the same time,the volume fraction of large particles increases in the bed.With the agglomeration,the volume-average mean particle size increases with the increase of gas velocity.Simulations show that the volume-average mean particle size increases with the increase of density of particles.