颗粒物料下落、反弹和堆积过程的数值模拟
发布时间：2018-11-27 14:04
【摘要】：颗粒物料在生产操作和生活活动中随处可见,而且是经济建设过程中不可或缺的材料。颗粒物料的存储、运输及使用等操作过程经常见到颗粒物料自由下落的现象,自由下落的颗粒物料会逃逸到空气中,造成局部甚至大面积的环境污染。粉尘进入空气会引发一系列的环境问题,在生产过程中产生的颗粒危害工作人员的身体健康、破坏生产设备、影响产品质量,颗粒物积累到一定浓度还可能引发尘爆;大量的颗粒物进入环境空气中造成大范围的污染,近些年我国北方城市频频出现的雾霾天气就与颗粒物大量进入空气有关。颗粒物料自由下落后与壁面接触反弹过程会引起二次扬尘,使颗粒扬尘的污染面积变大;下落物料对堆料形成的冲击也会引起二次扬尘。本论文在前人对气固两相流动研究的基础上,通过对气固两相流动运动规律的分析,掌握颗粒物料在空气中的运动规律,为控制颗粒物料自由下落引起的扬尘奠定基础,并对颗粒反弹和堆积过程进行数值模拟研究。本学位论文对圆球形、均一粒径的颗粒物料下落过程、反弹迁移过程和堆积过程的研究主要采用数值模拟的方法,利用基于有限元方法的流体计算软件COMSOL Multiphysics 5.0。针对物料下落的不同过程采用不同的物理模块来进行计算,主要用到湍流模块、流体流动粒子追踪模块以及动网格模块。在模拟研究中,引入基于曳力方程的流体与颗粒之间的相互作用力,在标准_(k-e)湍流模型中采用欧拉—拉格朗日方法研究,实现了流体相与颗粒相两相间的双向耦合,并通过对流体速度变化和颗粒速度变化的分析验证了本文双向耦合模拟气固两相流动的正确性;本文是运用克努森余弦定律和蒙特卡洛方法,进行了考虑颗粒与壁面碰撞后动量损失的随机反弹迁移过程的模拟;在对颗粒堆积过程的研究中提出通过网格变形来反映颗粒堆积的过程,在该方法中通过引入累加器作为中间变量将与下壁面接触颗粒的量转化为网格变形的量,最终通过网格的变形的形态反映颗粒堆积后的形态;同时观察了颗粒堆积后对流场流动的影响情况。模拟结果表明:颗粒粒径越大、下落高度越高、密度越大对流体的扰动也越大,同时颗粒群中的颗粒受到流体的影响比单颗粒大而且更加复杂,并不是颗粒数目简单相加的结果;颗粒反弹过程的模拟实现了考虑动量损失以及反弹后方向的随机的情况。虽然通过网格变形来反映颗粒的堆积取得了理想的结果,但与真实的颗粒堆积过程相比仍有差异。通过对比分析颗粒堆积与不堆积的流场速度变化情况,得出在研究颗粒二次扬尘问题时不可忽略颗粒堆积的影响。
[Abstract]:Granular materials can be found everywhere in production operation and daily activities, and they are indispensable materials in economic construction. In the process of storage, transportation and use of granular materials, the phenomenon of free drop of particle materials is often observed. The free falling particles will escape into the air, resulting in local or even large-scale environmental pollution. Dust entering the air will cause a series of environmental problems, the particles produced in the production process harm the health of workers, damage production equipment, affect the quality of products, particulate matter accumulation to a certain concentration may also lead to dust explosion; A large number of particles enter the ambient air and cause a wide range of pollution. In recent years, the frequent occurrence of haze weather in the northern cities of China is related to the large amount of particulate matter entering the air. The secondary dust will be caused by the contact with the wall after free falling of the particle material, and the pollution area of the particle dust will become larger, and the impact of the falling material on the formation of the pile material will also cause the secondary dust. On the basis of previous researches on gas-solid two-phase flow, through the analysis of gas-solid two-phase flow law, this paper grasps the movement law of particle material in air, and lays a foundation for controlling the dust caused by the free falling of particle material. The process of particle rebound and accumulation is studied numerically. In this dissertation, numerical simulation is used to study the falling process, rebound migration process and stacking process of spherical and homogeneous particles, and the fluid calculation software COMSOL Multiphysics 5.0 based on finite element method is used. Different physical modules are used to calculate the different processes of material falling, including turbulence module, fluid flow particle tracing module and moving mesh module. In the simulation study, the interaction force between fluid and particle is introduced based on the drag equation, and the Euler-Lagrange method is used in the standard _ (k-e) turbulence model to realize the bidirectional coupling between the fluid phase and the particle phase. The bidirectional coupling simulation of gas-solid two-phase flow is verified by the analysis of fluid velocity and particle velocity. In this paper, using Knudsen's cosine law and Monte Carlo method, the stochastic rebound migration process considering momentum loss after particle collision with wall is simulated. In the study of particle stacking process, the mesh deformation is proposed to reflect the particle stacking process. In this method, the amount of particles in contact with the lower wall is transformed into the mesh deformation by introducing an accumulator as an intermediate variable. Finally, the shape of the deformation of the mesh reflects the shape of the particles after the accumulation; At the same time, the influence of the flow in the flow field after the accumulation of particles was observed. The simulation results show that the larger the particle size, the higher the falling height, and the greater the density, the greater the disturbance to the fluid, and the more complex the influence of the particles in the particle group is than that of the single particle. It is not the result of simple addition of particle number; The simulation results show that the momentum loss and the direction after the rebound are considered randomly. Although the ideal results can be obtained by using mesh deformation to reflect the accumulation of particles, there is still a difference compared with the real process of particle stacking. By comparing and analyzing the velocity variation of particle accumulation and non-accumulation, it is concluded that the influence of particle accumulation should not be ignored in the study of particle secondary hoisting.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X513
本文编号：2361047
[Abstract]:Granular materials can be found everywhere in production operation and daily activities, and they are indispensable materials in economic construction. In the process of storage, transportation and use of granular materials, the phenomenon of free drop of particle materials is often observed. The free falling particles will escape into the air, resulting in local or even large-scale environmental pollution. Dust entering the air will cause a series of environmental problems, the particles produced in the production process harm the health of workers, damage production equipment, affect the quality of products, particulate matter accumulation to a certain concentration may also lead to dust explosion; A large number of particles enter the ambient air and cause a wide range of pollution. In recent years, the frequent occurrence of haze weather in the northern cities of China is related to the large amount of particulate matter entering the air. The secondary dust will be caused by the contact with the wall after free falling of the particle material, and the pollution area of the particle dust will become larger, and the impact of the falling material on the formation of the pile material will also cause the secondary dust. On the basis of previous researches on gas-solid two-phase flow, through the analysis of gas-solid two-phase flow law, this paper grasps the movement law of particle material in air, and lays a foundation for controlling the dust caused by the free falling of particle material. The process of particle rebound and accumulation is studied numerically. In this dissertation, numerical simulation is used to study the falling process, rebound migration process and stacking process of spherical and homogeneous particles, and the fluid calculation software COMSOL Multiphysics 5.0 based on finite element method is used. Different physical modules are used to calculate the different processes of material falling, including turbulence module, fluid flow particle tracing module and moving mesh module. In the simulation study, the interaction force between fluid and particle is introduced based on the drag equation, and the Euler-Lagrange method is used in the standard _ (k-e) turbulence model to realize the bidirectional coupling between the fluid phase and the particle phase. The bidirectional coupling simulation of gas-solid two-phase flow is verified by the analysis of fluid velocity and particle velocity. In this paper, using Knudsen's cosine law and Monte Carlo method, the stochastic rebound migration process considering momentum loss after particle collision with wall is simulated. In the study of particle stacking process, the mesh deformation is proposed to reflect the particle stacking process. In this method, the amount of particles in contact with the lower wall is transformed into the mesh deformation by introducing an accumulator as an intermediate variable. Finally, the shape of the deformation of the mesh reflects the shape of the particles after the accumulation; At the same time, the influence of the flow in the flow field after the accumulation of particles was observed. The simulation results show that the larger the particle size, the higher the falling height, and the greater the density, the greater the disturbance to the fluid, and the more complex the influence of the particles in the particle group is than that of the single particle. It is not the result of simple addition of particle number; The simulation results show that the momentum loss and the direction after the rebound are considered randomly. Although the ideal results can be obtained by using mesh deformation to reflect the accumulation of particles, there is still a difference compared with the real process of particle stacking. By comparing and analyzing the velocity variation of particle accumulation and non-accumulation, it is concluded that the influence of particle accumulation should not be ignored in the study of particle secondary hoisting.
【学位授予单位】：西安建筑科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：X513
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