Abstract:

Adopting two kinds of particles whose density is a little higher and lighter than fluid, the fluid dynamics in a bubble-driven liquid-solid fluidized-bed was studied. Air was introduced into the bottom as driving force and the liquid was continuous phase at the stationary phase. Pressure drops were measured and the videos were taken between different heights to estimate the initial fluidization gas velocity U_in,g, solid holdup and gas holdup. The initial fluidization gas velocity of heavy particles could be obtained by the variation of pressure drops at the bottom of the bed near gas distributor. While that of the light particles was determined by observation. The results showed that U_in,g of both the heavy and the light particles increase with solids loadings. The increasing tendency of the heavy particles at higher loadings becomes steep while that of the light particles is gentle. After fully fluidization, the axial distribution of solids holdup of the heavy particles is non-uniform comparing to the uniform distribution of the light particle solids holdup. When using binary particles, the fluidization of the upper light particles is influenced by the lower heavy particles. However, the heavy particles are not affected by the light particles. Thus U_in,g and the axial solids holdup of the heavy particles changes with heavy particle loadings. The light particle U_in,g varies with the total amount of binary particles.

Key words: fluidized-bed, bubble, multiphase flow, initial fluidization gas velocity, solid holdup, gas holdup

摘要：

采用密度稍重于和稍轻于流体的两种颗粒，研究了气泡驱动液固流化床内二元颗粒的流化行为。通过测量压差和拍摄视频的方法确定了初始流化气速U_in,g、固含率和气含率。重颗粒的U_in,g通过流化床底部的压差变化确定，轻颗粒的U_in,g则通过观察得到。研究表明,在气泡驱动的液固流化床内，重颗粒和轻颗粒的初始流化气速都随藏量的增加而增加，但重颗粒增加幅度更大。完全流化后，重颗粒固含率在轴向上分布不均匀，而轻颗粒则分布较为均匀。在二元颗粒体系内，上部轻颗粒的流化受到下部重颗粒的影响而底部重颗粒的流化不受轻颗粒影响，导致重颗粒U_in,g和固含率分布主要受自身藏量影响，而轻颗粒U_in,g随二元颗粒的总藏量变化。

关键词: 流化床, 气泡, 多相流, 初始流化气速, 固含率, 气含率