The origin of pressure oscillations in slugging fluidized beds: Comparison of experimental results from magnetic resonance imaging with a discrete element model
The origin of pressure oscillations in slugging fluidized beds: Comparison of experimental results from magnetic resonance imaging with a discrete element model
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DOI：
10.1016/j.ces.2014.05.041
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发表时间：
2014-09
影响因子：
4.7
通讯作者：
C. Boyce;J. Davidson;D. Holland;S. Scott;J. S. Dennis
中科院分区：
文献类型：
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作者：
C. Boyce;J. Davidson;D. Holland;S. Scott;J. S. Dennis
采用三维圆柱形离散元模型结合计算流体力学（DEM-CFD）研究了一次只能喷发一个气泡的鼓泡流化床和节涌流化床中压力振荡的起源。模拟具有各种沉降床高度和表观速度的直径为50 mm的床，用于与使用磁共振成像（MRI）和压力传感器获得的实验结果直接比较（Müller等人，2007年）。对于（i）分布器附近的压力振荡和（ii）床面处的气泡喷发的频率，理论预测与实验结果吻合得很好。在这两个模型和实验中，它被发现，分布器附近的压力振荡的频率匹配的气泡喷发的频率在床的顶部，而不是气泡形成的频率在分布器。进一步的模拟表明，床层中所有位置的压力振荡都源于颗粒对流体施加的拖曳力，而不是Müller等人（2007）提出的气泡喷发后产生的压力脉冲，随后通过床层向下传播。该理论还表明，拖曳力和因此的压降集中在“塞”中，即在床的水平横截面上填充有颗粒的区域。这些区域是最大的气泡喷发后的大小，导致压力振荡的频率，以配合气泡喷发。
A 3-D cylindrical discrete element model with computational fluid dynamics (DEM-CFD) was used to investigate the origin of pressure oscillations in bubbling and slugging fluidized beds in which only one bubble can erupt at a time. Beds 50 mm in diameter with various settled bed heights and superficial velocities were simulated for direct comparison with experimental results obtained using magnetic resonance imaging (MRI) and a pressure sensor (Müller et al., 2007). The theoretical predictions matched experimental results well for the frequencies of (i) pressure oscillations near the distributor and (ii) bubble eruption at the bed surface. In both model and experiment it was found that the frequency of pressure oscillations near the distributor matched the frequency of bubble eruption at the top of the bed, rather than the frequency of bubble formation at the distributor. Further simulations showed that pressure oscillations at all positions in the bed originated from the drag force imparted on the fluid by the particles, rather than from a pulse in pressure created upon bubble eruption and subsequently propagated down through the bed, as proposed by Müller et al. (2007). The theory also demonstrated that drag force and thus pressure drop was concentrated in “plugs”,viz.regions packed with particles across a horizontal cross section of the bed. These regions were largest in size after bubble eruptions, causing the frequency of pressure oscillations to match that of bubble eruption.