Visual investigations on radial solid holdup in vapor¿liquid¿solid fluidized bed evaporator with a CCD measuring system
Visual investigations on radial solid holdup in vapor¿liquid¿solid fluidized bed evaporator with a CCD measuring system
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DOI：
10.1016/j.ces.2005.08.006
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发表时间：
2006
影响因子：
4.7
通讯作者：
Mingyan Liu;Hong Wang;Ruixiao Lin
中科院分区：
文献类型：
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作者：
Mingyan Liu;Hong Wang;Ruixiao Lin
在前人对汽液固(V-L-S)沸腾外循环蒸发器流体力学和传热特性的可视化研究中，我们研制了一套白光电荷耦合器件测量系统(刘等，2004，利用电荷耦合器件测量技术研究汽液固三相流动沸腾系统的流体力学和传热特性)。化学工程科学59(4)，889)。在该方法中，将三维流场转换为二维(2D)图像，并记录下来，估计了加热管内固体颗粒在轴向位置的持气率和轴向速度分布。然而，由于在白炽灯光源下测量的2D图像中每个粒子的空间位置即使没有出现粒子重叠也很难确定，因此还没有评估固体持有率的径向分布。为此，本文选择并研制了一种结合激光薄片技术的面阵测量系统，通过拍摄二维流场图像，对V-L-S沸腾床蒸发器的径向固含率分布进行了检测。简要阐述了该方法的原理和步骤，并给出了典型结果。结果表明，在本实验条件下，加热管径向固含率分布不均匀，不同流型的固含率分布不同。在V-L-S沸腾流型下，轴心固含率高于加热管壁附近的固含率，而在L-S沸腾流型下，轴心固含率高于壁面固含率。还得到了固含率在径向的非对称分布。对观察到的实验事实给出了一些可能的定性解释和论证。这项工作可以为此类装置的学术描述和工业应用提供一些有价值的参考。
In previous visual investigations on the hydrodynamic and heat-transfer characteristics in an external natural circulating evaporator with vapor–liquid–solid (V–L–S) boiling flow, a charge-coupled device (CCD) measuring system with a white light source was developed (Liu et al., 2004, studies on the hydrodynamic and heat transfer in a vapor–liquid–solid flow boiling system with a CCD measuring technique. Chemical Engineering Science 59(4), 889). In this approach, a three-dimensional flow field was transformed into a two-dimensional (2D) image and was recorded, and the holdup and the axial linear velocity distributions of solid particles in an axial location in a heated tube were estimated. However, the radial distribution of solid holdup has not been evaluated because the space position of each particle in a 2D image measured under an incandescent lamp light source is difficult to determine even though the particle overlapping does not appear. Hence, a CCD measuring system combined with a laser sheeting technique was chosen and developed to examine the solid holdup profile in the radial direction in a V–L–S fluidized bed evaporator by taking images of 2D flow fields in this work. The principles and steps are briefly elucidated and typical results are given. It is shown that the solid holdups in the radial direction in a heated tube are not uniform and the profiles vary with the flow regimes under the present experimental conditions. The solid holdups in the axis center are higher than those near the wall of the heated tube with the V–L–S boiling flow regime, while the opposite is true for the L-S flow regime. Asymmetric distributions of solid holdups in the radial direction are also obtained. Some likely qualitative explanations and demonstrations on experimental facts observed are given. This work may provide some valuable references for academic descriptions and industrial applications of such an installation.