Abstract:

The study of mass transfer behaviors between bubble phase and emulsion phase is plays an important role in the design and regulation of fluidized bed reactor. The interaction between bubbles increases the complexity of mass transfer process. In this paper, computational fluid dynamics-discrete element method (CFD-DEM) was used to simulate the mass transfer process of two vertically distributed bubbles in a three-dimensional injected bubbling fluidized bed. On the basis of the independent determination method of mass transfer coefficients by convection and diffusion, the evolution of different mass transfer mechanisms with mutual interaction between bubbles was analyzed and the difference of mass transfer processes of two-bubbles and single-bubble was compared. The results showed that compared with the single bubble, the lower bubbles were axially stretched due to the existence of the upper bubbles. The volume of lower bubbles was reduced and the bubble rising velocity was increased. For the mass transfer process, the release of gas species from the upper bubbles increased the resistance of the diffusion-induced mass transfer of the lower bubbles and the reverse convective mass transfer was present. The interval of injection time further affected the mass transfer process. The complex mass transfer process of bubbles depended on many factors including the gas flow characteristics, the evolution of bubble shape and the concentration interference between bubbles.

Key words: fluidization, mesoscale, bubble, mass transfer, computational fluid dynamics-discrete element method

摘要：

气泡-乳化相相间传质行为是流化床反应器设计与调控的关键问题，气泡间的相互作用增加了相间传质过程的复杂性。本文利用CFD-DEM方法对三维射流鼓泡床内垂直分布的双气泡传质过程展开模拟，基于建立的对流-扩散传质系数独立确定方法，分析了气泡存在相互作用时不同传质机制的演变过程，对比了双气泡与单气泡传质过程的差异性。研究结果表明，与单气泡相比，上方气泡的存在会使得下方气泡轴向拉伸，减小了下方气泡体积并提高了气泡上升速度。对相间传质过程而言，上方气泡浓度的释放增加了下方气泡的扩散传质阻力，且使其出现逆向对流传质现象。不同入射时间间隔也会进一步影响传质过程，气泡复杂的传质过程将是气泡自身气流特性、形状演变与气泡间浓度干扰等多因素作用的结果。

关键词: 流态化, 介尺度, 气泡, 传质, CFD-DEM方法