化工学报 ›› 2022, Vol. 73 ›› Issue (6): 2636-2648.doi: 10.11949/0438-1157.20220158

• 流体力学与传递现象 • 上一篇    下一篇

磁场对湿颗粒流化床系统中介尺度结构影响机制研究

唐天琪1,2(),何玉荣1,2()   

  1. 1.哈尔滨工业大学能源科学与工程学院，黑龙江 哈尔滨 150001
    2.黑龙江省新型储能材料与储能过程研究重点实验室，黑龙江 哈尔滨 150001
  • 收稿日期:2022-02-07 修回日期:2022-05-08 出版日期:2022-06-05 发布日期:2022-06-30
  • 通讯作者: 何玉荣 E-mail:tangtianqi@hit.edu.cn;rong@hit.edu.cn
  • 作者简介:唐天琪（1993—），女，博士，讲师，tangtianqi@hit.edu.cn
  • 基金资助:
    国家自然科学基金项目(52076059)

Effect of magnetic field on the mesoscale structure evolution process in a wet particle fluidized bed

Tianqi TANG1,2(),Yurong HE1,2()   

  1. 1.School of Energy Science and Engineering, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China
    2.Heilongjiang Key Laboratory of New Energy Storage Materials and Processes, Harbin Institute of Technology, Harbin 150001, Heilongjiang, China
  • Received:2022-02-07 Revised:2022-05-08 Published:2022-06-05 Online:2022-06-30
  • Contact: Yurong HE E-mail:tangtianqi@hit.edu.cn;rong@hit.edu.cn

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摘要：

湿颗粒系统在自然界及工业过程非常普遍，例如喷雾造粒、反应器中矿物黏结、催化以及制药等，这其中含有大量典型介尺度结构如颗粒聚团、结块以及气泡等结构，这些结构的存在导致颗粒系统的流动及热质传递特性发生明显改变。针对鼓泡流化床湿颗粒系统中颗粒聚团以及气泡等介尺度结构，应用离散单元模型并引入外加磁场，研究磁场作用下湿颗粒系统中介尺度结构的演化机制，探究磁场力、液桥力、接触力对气泡演化过程的影响。研究发现，在不考虑磁场的条件下，颗粒易形成聚团并存在气泡边界不规则等现象，引入外加匀强磁场后，磁场力对鼓泡流化床内气泡结构存在破坏和抑制作用。

关键词: 湿颗粒, 离散单元模型, 磁场, 介尺度

Abstract:

Wet particle systems are very common in nature and industrial processes, such as spray granulation, mineral bonding in reactors, pharmaceutical and catalyst. Due to the presence of liquid, the flow, heat and mass transfer characteristics are significantly changed compared with dry particle systems. For example, a large number of typical mesoscale structures, including particle agglomeration, clusters and bubbles, form and lead to different flow regime. Thus, mesoscale structure flow and evolution behaviors have attracted more and more attention, which might affect the design and operation of industrial reactors. In this paper, typical mesoscale structures are investigated in a bubbling fluidized bed by discrete element method (DEM), and effect of external magnetic field on mesoscale structure evolution process is explored. First, the numerical model for describing dry and wet particle system flow behaviors were established with magnetic field introduced. The numerical model has been validated and shown in our previous published investigations. Then, mesoscale structure flow behaviors were analyzed in dry and wet particle system without magnetic flied. Bubble evolution process was found clearly in a dry particle system, and the trajectory of the bubble was almost along the midline of fluidized bed. With the cohesive liquid introduced, that of bubble center was offset from the midline. Next, an external magnetic field was introduced based on DEM to study the evolution mechanism of the mesoscale structure in the wet particle system under the action of the magnetic field. We compared the dominant role of liquid bridge force, contact force, magnetic force and drag force in fluidized beds, and tried to analyze and explore the relationship among different forces. The study found that without considering the magnetic field, particles are easy to form agglomeration and have irregular bubble boundaries. After the introduction of an external uniform magnetic field, the magnetic field force will destroy and inhibit the bubble structure in the bubbling fluidized bed.

Key words: wet particle, discrete element method, magnetic field, mesoscale structure

中图分类号: 

  • TK 11

图1

磁场作用下含湿磁性颗粒受力情况示意图"

表1

模拟参数设置"

变量数值单位变量数值单位
流化床气体
鼓泡床x、y、z方向尺寸90×24×900mm气体密度1.2kg/m3
鼓泡床x、y、z方向网格10×3×90气体速度1.2m/s
颗粒气体黏度1.8×10-5Pa?s
颗粒数量16000个出口压力101325Pa
颗粒直径3mm液体
颗粒密度420kg/m3相对液体量0.01%
恢复系数0.97液体密度1000kg/m3
颗粒间滑动摩擦系数0.10液体黏度1.03mPa?s
颗粒壁面间滑动摩擦系数0.30接触角π/6rad
法向弹簧刚度800N/m表面张力系数0.0721N/m
切向弹簧刚度286N/m磁场
颗粒磁化率0.642磁场强度0.005，0.010，0.020T

图2

流化床结构示意图"

图3

无磁场作用下一个气泡生长周期内颗粒空间分布情况"

图4

无磁场作用下床层压降脉动及一个气泡生长周期内气泡生长情况"

图5

干、湿颗粒系统中气泡颗粒温度分布情况"

图6

不同磁场强度下一个气泡生长周期内颗粒空间分布情况"

图7

不同磁场强度下气泡颗粒温度分布情况"

图8

不同磁场强度下床层压降脉动及一个气泡生长周期内气泡生长情况"

图9

梯度磁场对一个气泡生长周期内气泡生长情况的影响"

图10

气泡区域垂直方向磁场力、接触力、曳力以及液桥力之间的相互作用机制"

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