振动流化床中颗粒运动特性的实验研究与数值模拟

发布时间：2018-02-11 15:33

本文关键词： 振动流化床流体力学欧拉模型 DEM模型 CFD数值模拟　出处：《青岛科技大学》2015年硕士论文　论文类型：学位论文

【摘要】：振动流化床是将机械振动的能量加入到流化床的一种流化床形式,由于振动力的加入可以降低床层压降、起始流化的速度,提高床层的均一性和稳定性等优点,并且振动流化设备是一种具有高效传质传热特性的设备,所以广泛地应用于干燥、喷雾造粒及分选等诸多工业过程。随着CFD的不断发展,将理论分析和计算结合的数值方法越来越展现巨大的发展潜力,对于多相流研究起着重要作用。本文采用CFD数值模拟方法,利用流体力学模拟软件Fluent,自行编写振动网格UDF程序,对振动流化床内局部流体力学特性进行了系统的模拟研究。通过数值模拟与实验测定结果的比较分析,为设计开发此类反应器、优化过程操作和提高反应效率提供详细的数据支持和可靠的理论指导。(1)综述了前人对振动流化床实验与数值模拟等多方面的研究进展。欧拉方法是最早应用到流化床模拟的方法之一,但是欧拉模型不考虑颗粒的尺寸、形状、碰撞等微观特点,相比而言DEM模型更适合研究振动流化床,而且所需经验参数较少。但是由于DEM模型复杂将消耗大量计算时间,以往文献只是针对二维振动流化床或伪二维振动流化床进行模拟,颗粒数量级较小,并不能准确反应振动流化床的颗粒运动特性。这些问题是进行本文研究工作的原因。(2)对二维振动流化床进行了实验研究和数值模拟,实验研究了振动流化床中床层压降的变化,并采用欧拉模型模拟了振动方向、固含率、颗粒速度的影响。实验研究发现振动力的加入会增强颗粒的流动性,床层压降更接近于理论值。数值模拟发现竖直振动作用使床层底部形成低颗粒浓度区域,振动间隙出现并产生大气泡,而水平作用使床体侧壁出现振动间隙；振动强度的增大有利于流化效果,振动频率增大到一定程度效果减弱。(3)采用DEM模型的CFD数值模拟方法,突破以往二维模型、少量颗粒的数值模拟限制,建立了10万颗粒数量级的三维模型。模型能更好的模拟三维振动流化床各个方向颗粒碰撞,更真实的预测流体流动特性和颗粒的分布,随着计算机技术的不断发展,10万颗粒数量级的三维模型模拟时间更快了。研究了振动对固含率、颗粒速度、床层空隙率等的影响。
[Abstract]:Vibratory fluidized bed is a kind of fluidized bed in which the energy of mechanical vibration is added to the fluidized bed. Because of the addition of vibration force, the pressure drop of bed can be reduced, the velocity of initial fluidization can be reduced, and the uniformity and stability of bed can be improved. And vibratory fluidization equipment is a kind of equipment with high efficiency mass transfer and heat transfer, so it is widely used in drying, spray granulation and sorting, etc. With the development of CFD, The numerical method which combines theoretical analysis with calculation has more and more great potential for development and plays an important role in the study of multiphase flow. In this paper, the CFD numerical simulation method and fluid dynamics simulation software Fluentare used to write the UDF program of vibrating grid. The characteristics of local fluid dynamics in vibratory fluidized bed were studied systematically. By comparing the results of numerical simulation and experimental measurement, the authors developed this kind of reactor in order to design and develop this kind of reactor. Optimization of process operation and improvement of reaction efficiency provide detailed data support and reliable theoretical guidance. (1) A review of previous researches on vibratory fluidized bed experiments and numerical simulation is presented. Euler method is the first to be applied to flow. One of the methods of chemical bed simulation, However, the Euler model does not take into account the microscopic characteristics of particle size, shape and collision. Compared with the DEM model, it is more suitable for the study of vibratory fluidized beds and requires less empirical parameters. However, because of the complexity of the DEM model, a large amount of computational time will be consumed. In the past, only two-dimensional vibrating fluidized beds or pseudo-two-dimensional vibrating fluidized beds were simulated, and the order of magnitude of particles was relatively small. These problems are the reason for the research work in this paper. The experimental study and numerical simulation of two-dimensional vibrating fluidized bed are carried out, and the variation of bed pressure drop in vibrating fluidized bed is experimentally studied. Euler model was used to simulate the effects of vibration direction, solid holdup and particle velocity. The pressure drop of the bed is closer to the theoretical value. The numerical simulation shows that the vertical vibration results in the formation of low particle concentration region at the bottom of the bed, the vibration gap appears and produces large bubbles, and the horizontal action results in the vibration gap on the side wall of the bed. The increase of vibration intensity is beneficial to the fluidization effect. The vibration frequency increases to a certain extent and weakens. The CFD numerical simulation method based on DEM model is used to break through the limitation of numerical simulation of two dimensional model and a small amount of particles. A three-dimensional model of 100,000 particle order is established. The model can better simulate particle collision in all directions of three-dimensional vibrating fluidized bed, and more truly predict the fluid flow characteristics and particle distribution. With the development of computer technology, the simulation time of 3D model of 100,000 particle order is faster. The effects of vibration on solid holdup, particle velocity and bed voidage are studied.
【学位授予单位】：青岛科技大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TQ051.13

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