关键词: 流态化, 介尺度, 气泡, 传质, CFD-DEM方法

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