Valverde Jose Manuel, Castellanos Antonio
Faculty of Physics, Universidad de Sevilla, Spain.
Phys Rev E Stat Nonlin Soft Matter Phys. 2006 May;73(5 Pt 2):056310. doi: 10.1103/PhysRevE.73.056310. Epub 2006 May 24.
Fine particles agglomerate in the fluidized state due to the strength of interparticle attractive forces as compared to particle weight. Interparticle adhesion can be largely increased by consolidation stresses applied during powder handling. As a consequence, fragments of the consolidated powder may persist when the powder is fluidized, which gives rise to large agglomerates of strongly adhered particles in fluidization. This history-dependent effect can be minimized by coating the particles with surface additives such as silica nanoparticles. In this paper, we investigate the effect of high consolidation stresses sigma(c) previously applied to samples of silica-coated fine particles on their fluidization behavior. Our experimental measurements show that, even though homogeneous fluidization is still observed, the average agglomerate size and fractal dimension of the agglomerates increase as sigma(c) is increased. Bed expansion in the fluidized state is hindered by previously applied high consolidations, which we attribute to an increase of the largest stable size of mesoscopic fluid pockets. As a consequence, we observe that the initiation of macroscopic bubbling is delayed up to larger values of the fluid velocity.
与颗粒重量相比，由于颗粒间吸引力的作用，细颗粒在流化状态下会团聚。在粉末处理过程中施加的固结应力可大大增加颗粒间的附着力。因此，当粉末流化时，固结粉末的碎片可能会残留下来，这会导致流化过程中形成大量由强粘附颗粒组成的团聚体。通过用二氧化硅纳米颗粒等表面添加剂包覆颗粒，可以将这种历史依赖性效应降至最低。在本文中，我们研究了先前施加于二氧化硅包覆细颗粒样品的高固结应力σ(c)对其流化行为的影响。我们的实验测量表明，尽管仍观察到均匀流化，但随着σ(c)的增加，团聚体的平均尺寸和分形维数会增大。先前施加的高固结作用会阻碍流化状态下的床层膨胀，我们将其归因于介观流体袋最大稳定尺寸的增加。因此，我们观察到宏观鼓泡的起始会延迟到更高的流体速度值。
