Abstract:

Based on framework combined discrete element method and computational fluid dynamics, a gas-solid flow model in three-dimensional spouted bed was established and Fortran numerical simulation program was further developed. The mixing characteristics of two different diameter-sized wet or dry particles in three-dimensional spouted bed were simulated and the mixing mechanism of binary particles in the spouted bed was analyzed. Lacey mixing index was introduced to quantitatively analyze degree of mixing in whole bed and specific regions of the bed. The influences on mixing different sized particles were studied by volume of liquid bridge, ratio of particle densities and superficial gas velocity. The results show that both wet and dry particles flow similarly in single jet spouted bed without obvious agglomeration of wet particles. Liquid bridge had a greater influence on small particles than large ones, which reduced difference of velocity between wet particles with different diameters. Particle mixing in circular groove was critical to mixing across whole bed. Liquid bridge volume had a more significant influence on particle mixing, compared to ratio of particle densities and superficial gas velocity.

Key words: wet particle, two-phase flow, mixing, discrete element method, numerical simulation

摘要：

基于计算流体力学-离散单元法，建立了三维喷动床内气固两相流数学模型，采用Fortran语言编制了并行数值模拟程序。对三维喷动床内两种不同直径的干颗粒及湿颗粒的混合特性进行了数值模拟，并从颗粒角度分析了双组分颗粒的运动机制。利用Lacey混合指数对床内整体以及特定区域的混合程度进行了定量分析，并研究了液桥体积、颗粒密度比以及表观气速对异径颗粒混合的影响。结果表明：在单孔射流喷动床内，干湿两种颗粒流动方式相似，湿颗粒无明显的聚团现象；液桥力对小直径的颗粒影响较大，使不同直径湿颗粒速度差减小；环隙区内颗粒的混合是影响整床颗粒混合的关键因素；液桥体积对颗粒混合的影响较大，对颗粒密度比以及表观气速的影响有限。

关键词: 湿颗粒, 两相流, 混合, 离散单元法, 数值模拟