固液两相流中固体颗粒的垂直分选机理

Mechanism of vertical segregation of solid particles in sediment-laden flow

在结构两相流的总体框架内 ,基于对单个固相颗粒受力的分析和对多颗粒条件下颗粒之间的相互作用 ,本文对液体流动特性进行了简化 ,采用固体颗粒在水流中运动的垂线分选模型[1] ,对各种颗粒浓度条件下的垂直分选特征进行了讨论。结果表明 :随着颗粒浓度的增加 ,颗粒的分选过程加快 ,颗粒向上聚集的倾向加强 ,分选的结果会形成明显地在垂直方向上显示出反粒序分布。当颗粒体积浓度超过 0 .3以后 ,粗颗粒较细颗粒具有更大的向上聚集的倾向 ;当颗粒浓度接近极限浓度时 ,会出现颗粒分选速度的反常变化 ,说明分选模型在这种情况下失效。文中还通过常见的三种液相速度分布 。

Within the framework of the conceptual solid-liquid two-phase flow. multi-particle motion is discussed in terms of the force analysis on particles, the simplication of fluid flow and the consideration of particle-particle interaction. The model developed in the companion paper is used for describing vertical segregation of solid particles in solid-liquid two-phase flow. It is shown that the increase of sediment concentration would speed up the vertical sorting process and enhance the upward motion of particles as the volume concentration exceeding certain threshold about C>0.3, which is particularly apparent for coarse particles. As a result, the vertical sorting of non-uniform particles could form abnormal vertical distribution of particle size with coarser particles in the upper region. Correspondingly, abnormal profiles could be formed in hyper-concentrated sediment-laden flow, which show the larger concentration in the upper region and the lower in the near-bed region. One of the restrictions of the present model is that it could not be valid when particle concentration approximate to the limit concentration. In addition, three types of conventional velocity distributions of liquid flow are used for evaluation of their effect to the vertical sorting results. The comparison of the results shows that there is no essential influence of different velocity profiles on the vertical sorting patterns of particles.