Single bubble behavior in gas-liquid-solid mini-fluidized beds
Single bubble behavior in gas-liquid-solid mini-fluidized beds
复制标题
气-液-固小型流化床中的单气泡行为
DOI：
10.1016/j.cej.2015.10.071
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发表时间：
2016
影响因子：
15.1
通讯作者：
Li Xiangnan
中科院分区：
文献类型：
--
作者：
Li Yanjun;Liu Mingyan;Li Xiangnan
气-液-固微型流化床是一种重要的新型反应器。然而，在这样的系统中的流动行为没有得到很好的理解，即使是单个气泡的特性。采用可视化实验研究了2-10 mm尺寸的三相并流上行微型流化床的初始流化、单个气泡的运动和尺寸。结果表明，对于较小的流化床，由于气泡在较低的表观液速下发生聚并，床层压降随时间的变化是一个强烈的波动，而对于10 mm的流化床，液固和气液固体系的最小流化速度在实验范围内没有明显差异。壁面效应对气泡尺寸的影响占主导地位。较强的壁面效应减小了悬浮惯性力，导致气泡尺寸减小。在较低的孔板气速下，气泡尺寸主要受表面张力和浮力的平衡控制，而在三相微型流化床中，悬浮惯性力对气泡尺寸起着更重要的控制作用。此外，气相的可压缩性有助于气泡尺寸的变化;即使对于这样的小固体颗粒也观察到气泡尾流，并且可以在相对高的孔板气体速度下影响较小床中的以下气泡尺寸。提出了预测三相微型流化床中气泡直径的经验公式。
Gas–liquid–solid mini-fluidized bed is a new and important reactor. However, the flow behavior in such a system is not well understood, even for the characteristics of single bubble. Initial fluidization, movement and size of singe bubble in three-phase co-current upward mini-fluidized beds of 2–10 mm sizes were studied with visual experiments. The results show that the variation of pressure drop across the bed with time is a strong fluctuation due to the coalescence of bubbles at lower superficial liquid velocities for smaller beds, while no obvious difference in the minimum fluidization velocity between the liquid–solid and gas–liquid–solid systems for a 10 mm MFB exists in the experimental ranges. The wall effect on the bubble size is dominant. The stronger wall effect decreases suspension inertial force, which leads to the diminution of bubble size. A force balance between the surface tension force and buoyant force dominates the bubble size in mini-bubble column at lower orifice gas velocities, while suspension inertial force plays more important role in governing the bubble size in three-phase mini-fluidized beds. Additionally, compressibility of the gas phase contributes to the variation in the bubble size; the bubble wake is observed even for such small solid particles, and can affect the following bubble size in smaller beds at relative high orifice gas velocities. An empirical equation was suggested to predict the bubble diameters in three-phase mini-fluidized beds.