窄缝流化床中的结晶和堵塞
Crystallization and jamming in narrow fluidized beds
摘要：
流化床基本上是颗粒材料通过管中的上升流体的悬浮，并且其具有包括聚集和斑图形成的丰富动力学。当管直径和颗粒直径之间的比率较小时，高约束效应可以诱导不同的行为。一些意想不到的和好奇的行为，我们在本文中调查，是结晶和堵塞的颗粒在液体中的速度高于初始流化，应该保持颗粒流化。在我们的实验中，在透明材料的垂直管中进行，使用不同的颗粒、水速度、静止时间和速度减速。基于图像处理的床演变的分析表明，在减少的流量达到的速度仍然高于初始流化，颗粒变得组织在晶格结构的高紧凑性，在那里他们被困，虽然与小的波动。这些结构最初是局部化的，并且以与相变和玻璃形成中发生的类似方式随时间生长。经过一定时间后，如果液体速度稍微增加，就会发生堵塞，颗粒被完全阻挡，其波动消失。我们发现，不同的晶格结构出现取决于晶粒类型。我们的研究结果提供了新的见解流化条件，玻璃状的形成和堵塞。
英文摘要：
A fluidized bed is basically a suspension of granular material by an ascending fluid in a tube, and it has a rich dynamics that includes clustering and pattern formation. When the ratio between the tube and grain diameters is small, different behaviors can be induced by high confinement effects. Some unexpected and curious behaviors, that we investigate in this paper, are the crystallization and jamming of grains in liquids with velocities higher than that for incipient fluidization, supposed to maintain the grains fluidized. In our experiments, performed in a vertical tube of transparent material, different grains, water velocities, resting times, and velocity decelerations were used. An analysis of the bed evolution based on image processing shows that, after a decreasing flow that reaches a velocity still higher than that for incipient fluidization, grains become organized in lattice structures of high compactness, where they are trapped though with small fluctuations. These structures are initially localized and grow along time, in a similar manner as happens in phase transitions and glass formation. After a certain time, if the liquid velocity is slightly increased, jamming occurs, with grains being completely blocked and their fluctuation disappearing. We show that different lattice structures appear depending on the grain type. Our results provide new insights into fluidization conditions, glass-like formation and jamming.
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