首页> 外文学位 >文献详情
【24h】

Investigation of coalescence and breakup of bubble in packed-bed .

机译:填充床中气泡的聚结与破裂研究。

获取原文
获取原文并翻译 | 示例

摘要

Model of bubble interactions of breakup and coalescence in a two-dimensional packed-bed reactor has been developed for dispersed two-phase flow conditions. Image processing techniques are used to study dominant bubble mechanisms at pore level under the bubbly flow regime. Bubble breakup and coalescence are identified as dominant mechanisms from analysis using a large number of image samples. Two types of coalescence mechanisms are identified that occur due to compression and deceleration associated with the bubbles and three breakup mechanisms are identified that are result of liquid shear force, bubble acceleration, and bubble-to-bubble impact.;The two-dimensional packed-bed system is designed and built with two different inlets: one is for uncontrolled sized bubbles, and the other is for controlled sized bubbles. For uncontrolled sized bubbles, bubble images are taken at a single axial location in order to study changes of two-phase parameters as well as bubble size PDF (population density function) distribution with different gas and liquid superficial velocities. For controlled sized bubbles, bubble images are taken at multiple axial locations in order to study changes of bubble size PDF distribution from inlet to the far downstream. Bubble breakup and coalescence dominated flow regimes near the inlet have been simulated by adjusting appropriate flow rates of air and water.;Data on various two-phase parameters, such as local void fraction, bubble velocity, size, number, and shape are obtained from assessment of the bubble images. Results indicate that when a flow regime changed from bubbly to either trickling or pulsing flow, the number of average sized bubbles significantly decreases and the shape of the majority of the bubbles is no longer spherical. Although a mean bubble velocity of all sized bubbles is uniform for given gas and liquid superficial velocities, individual bubble velocities are quite different depending on the bubble location in the pore. The bubble size PDF distributions taken for the uncontrolled sized bubbles are compared with previous studies and the results on bubble size are in general agreement. Bubble size PDF distributions under either bubble breakup or coalescence dominated flow regimes change rapidly near the inlet and slowly far away from the inlet. The median as a function of axial locations show how the bubble size distributions propagate along the axial direction. The different initial medians of the bubble breakup and coalescence dominated flows reach the same final median far downstream.;Based on the experimental observations, bubble interaction models to predict bubble size PDF distribution along the axial direction are developed by modifying existing models as well as adding new geometry effects due to the complex and narrow channels. For breakup, an additional pressure term is added and surface tension stress is modified due to bubble-to-solid collision. For coalescence, probability of bubble collision, and cross sectional area of bubbles are modified due to restricted flow channels. Pressure ratios enhance the breakup and the coalescence near packing. A velocity ratio enhances the coalescence at vertical narrow channels. The developed mechanistic bubble interaction models are implemented in a commercial CFD code, CFX-4.0, which solves population balance equations for dispersed gas-liquid flows. To validate the present bubble interaction models of breakup and coalescence, bubble breakup and coalescence dominated flow regimes near the inlet are separately simulated and the bubble size PDF distributions estimated by CFD analyses are compared with experimental data.;As a result, the estimated bubble size distributions for the bubble breakup and coalescence dominated flows are comparable with each other and their median variations along the axial direction agree with the experimental data. With the adjusted coalescence coefficients, the estimated medians fall within the uncertainties.
机译:针对分散的两相流条件,开发了二维填充床反应器中破裂和聚结的气泡相互作用模型。图像处理技术用于研究气泡流状态下孔隙水平的主要气泡机制。通过使用大量图像样本进行分析,可以确定气泡破裂和聚结是主要机制。识别出两种类型的聚结机理,它们是由于气泡的压缩和减速而产生的,而三种破碎机理是由于液体剪切力,气泡加速度和气泡对气泡的冲击而产生的。床系统的设计和建造有两个不同的入口:一个用于大小不受控制的气泡,另一个用于大小受控的气泡。对于不受控制的大小的气泡,在单个轴向位置拍摄气泡图像,以便研究两相参数的变化以及气泡尺寸PDF(人口密度函数)分布在不同气体和液体表面速度下的分布。对于受控大小的气泡,在多个轴向位置拍摄气泡图像,以便研究气泡尺寸PDF分布从进口到远处下游的变化。通过调节合适的空气和水的流速来模拟入口附近的气泡破裂和聚结为主的流动状态。;获得各种两相参数的数据,例如局部空隙率,气泡速度,大小,数量和形状气泡图像的评估。结果表明,当流态从气泡流变为滴流或脉动流时,平均大小的气泡数会显着减少,并且大多数气泡的形状不再是球形。尽管对于给定的气体和液体表观速度,所有大小气泡的平均气泡速度都是均匀的,但各个气泡速度却有很大不同,具体取决于气泡在孔中的位置。将不受控制大小的气泡的气泡尺寸PDF分布与以前的研究进行了比较,并且气泡尺寸的结果基本一致。在气泡破裂或聚结为主的流动状态下,气泡大小PDF分布在入口附近迅速变化,而在远离入口处缓慢变化。中值作为轴向位置的函数显示了气泡尺寸分布如何沿轴向传播。气泡破裂和合并主导流的不同初始中值到达下游的最终最终中值相同。基于实验观察结果,通过修改现有模型并添加一些模型,开发了可预测沿轴向气泡尺寸PDF分布的气泡相互作用模型。复杂而狭窄的通道带来了新的几何效果。对于破裂,由于气泡与固体的碰撞,增加了一个附加的压力项,并且改变了表面张力应力。对于聚结,由于受限制的流动通道而改变了气泡碰撞的可能性和气泡的横截面积。压力比增强了填料附近的破裂和聚结。速度比增强了垂直窄通道处的合并。所开发的机械气泡相互作用模型是在CFD商业代码CFX-4.0中实现的,该模型解决了分散的气液流动的总体平衡方程。为了验证目前的破裂和合并的气泡相互作用模型,分别模拟了入口附近的破裂和合并主导的流动状态,并将通过CFD分析估算的气泡尺寸PDF分布与实验数据进行了比较;结果,估算的气泡尺寸气泡破裂和聚结主导的流动的分布彼此可比,并且它们沿轴向的中值变化与实验数据一致。通过调整聚结系数,估计中位数将落在不确定性范围内。

著录项

  • 作者

    Jo, Daeseong.;

  • 作者单位

    Purdue University.;

  • 授予单位 Purdue University.;
  • 学科 Engineering Chemical.;Engineering Nuclear.
  • 学位 Ph.D.
  • 年度 2010
  • 页码 212 p.
  • 总页数 212
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

相似文献

  • 外文文献
  • 中文文献
  • 专利
获取原文

联系方式:18141920177 (微信同号)

客服邮箱:kefu@zhangqiaokeyan.com

京公网安备:11010802029741号 ICP备案号:京ICP备15016152号-6 六维联合信息科技 (北京) 有限公司©版权所有
  • 客服微信

  • 服务号