Mahajan Vinay V, Padding Johan T, Nijssen Tim M J, Buist Kay A, Kuipers J A M
Dept. of Process and Energy Delft University of Technology 2628 CB Delft The Netherlands.
Dept. of Chemical Engineering & Chemistry, Multiphase Reactors Group Eindhoven University of Technology 5600 MB Eindhoven The Netherlands.
AIChE J. 2018 May;64(5):1573-1590. doi: 10.1002/aic.16078. Epub 2018 Feb 6.
Fluidization is widely used in industries and has been extensively studied, both experimentally and theoretically, in the past. However, most of these studies focus on spherical particles while in practice granules are rarely spherical. Particle shape can have a significant effect on fluidization characteristics. It is therefore important to study the effect of particle shape on fluidization behavior in detail. In this study, experiments in pseudo-2D fluidized beds are used to characterize the fluidization of spherocylindrical (rod-like) Geldart D particles of aspect ratio 4. Pressure drop and optical measurement methods (Digital Image Analysis, Particle Image Velocimetry, Particle Tracking Velocimetry) are employed to measure bed height, particle orientation, particle circulation, stacking, and coordination number. The commonly used correlations to determine the pressure drop across a bed of nonspherical particles are compared to experiments. Experimental observations and measurements have shown that rod-like particles are prone to interlocking and channeling behavior. Well above the minimum fluidization velocity, vigorous bubbling fluidization is observed, with groups of interlocked particles moving upwards, breaking up, being thrown high in the freeboard region and slowly raining down as dispersed phase. At high flowrates, a circulation pattern develops with particles moving up through the center and down at the walls. Particles tend to orient themselves along the flow direction.
流化在工业中被广泛应用，并且在过去已经从实验和理论两方面进行了广泛研究。然而，这些研究大多集中在球形颗粒上，而在实际中颗粒很少是球形的。颗粒形状对流化特性可能有显著影响。因此，详细研究颗粒形状对流化行为的影响很重要。在本研究中，利用二维流化床实验来表征长径比为4的球柱状（棒状）Geldart D颗粒的流化情况。采用压降和光学测量方法（数字图像分析、粒子图像测速、粒子跟踪测速）来测量床层高度、颗粒取向、颗粒循环、堆积以及配位数。将用于确定非球形颗粒床层压降的常用关联式与实验进行了比较。实验观察和测量表明，棒状颗粒容易出现联锁和沟流行为。在远高于最小流化速度时，观察到剧烈的鼓泡流化，成组的联锁颗粒向上移动、破碎，被抛到自由空域并作为分散相缓慢落下。在高流速下，形成一种循环模式，颗粒在中心向上移动，在壁面处向下移动。颗粒倾向于沿流动方向排列自身。
