【作者】 曹文广；

【导师】 刘海峰；

【作者基本信息】 华东理工大学 ， 热能工程， 2013， 博士

【摘要】 本文以粉煤气化气化技术为背景,采用高速摄像仪、粒子图像计算软件和Fluent等,对稠密气固两相射流过程中的颗粒弥散、颗粒运动特征等关键科学问题进行了实验研究,并建立了相关模型进行了数值模拟。具体总结如下：1.采用高速摄像仪拍摄了颗粒射流的运动状态,通过对所拍摄得到的图片进行分析获得了颗粒射流的弥散特征。结果表明：颗粒表观速度对颗粒流弥散宽度、颗粒流核心大小和颗粒弥散边界层大小等弥散特征量都有重要的影响；颗粒弥散宽度和弥散边界层大小首先随着距喷嘴距离的增大而呈线性增长然后保持一定大小不变；颗粒弥散边界层中颗粒的竖直速度分布可用抛物线表示；喷嘴角度能对颗粒径向速度产生一定的影响,进而影响颗粒弥散特征量的变化。2.对平行喷嘴中颗粒流的弥散特征以及弥散模式进行了分析,同时也对颗粒流在交叉射流中的弥散特征进行了分析。通过分析颗粒的受力情况导出了颗粒流未扰动长度的计算公式；提出了用于计算颗粒流弥散长度的卷吸模型,通过推导获得了弥散长度的表达式；分析了不同交叉角下颗粒流的最小直径和其出现的位置,并获得了其计算公式；引入了Strouhal数来划分波状弥散与振荡弥散,发现波状弥散范围内,第一个波的Strouhal数为0.03～0.07,而振荡弥散时Strouhal数为0.01CO20.02,过渡状态的Strouhal数为0.02～0.03。3.应用数值模拟的方法,研究了自由空间中颗粒流在同轴交叉射流中的弥散。采用Realizable k-ε模型模拟湍流,离散颗粒法模拟颗粒运动,颗粒间的碰撞采用概率碰撞模型。结果表明,随着交叉角的增大,气相的轴向速度越来越大,但轴线速度并不无限增大：气流和颗粒流交界处的湍动能高于其它位置,这有利于颗粒的弥散。在气固交界面,颗粒间的碰撞最为激烈。4.通过对稠密气固两相流方程的重整,在考虑空隙率对流场影响及颗粒间碰撞的作用下建立了颗粒射流在同轴气流中弥散的二维大涡-离散颗粒法模型(LES-DPM)。模拟获得了同轴射流中颗粒流弥散的整体流场特征,在喷嘴附近气流与颗粒流之间存在回流能导致颗粒对喷嘴的磨损。获得了喷嘴轴线处气体速度分布、颗粒的速度浓度分布以及碰撞频率随弥散模式的变化规律,轴线处颗粒速度、浓度和气体速度等能反应颗粒流的弥散状态；探讨了颗粒流弥散的机理,从气固相互作用(包括曳力系数的非线性性和操作压力)以及颗粒间的碰撞或颗粒间的能量传递揭示了颗粒流的弥散模式的产生是受两者相互作用的影响,且曳力系数的非线性性占主导地位。更多还原

【Abstract】 This study is conducted to understand the fundamental questions of the dense gas-particle jet and to develop a numerical model. Using high speed camera, software of particle image velocimetry, and Fluent software, the characteristics of particles dispersion and particles motion are studied through experiment and simulation on the basis of pulverized coal gasification. The main contents and results are summartized as follows:1. The dispersion characteristics of the granular jet are obtanined using a high speed camera. The results show that the surperfical velocity of particles plays an important role in the characteristics of the near field of the granular jet (e.g., the diameter of granular jet core, the width of dispersed jet, and the thickness of boundary layer). The width of dispersed jet and the thickness of boundary layer linearly grow with the distance from the nozzle exit at first and then keep a constant. The velocity profile of boundary layer near the nozzle exit is parabolic distribution. In addition, the nozzle angle has an influence on the radial velocity of particles and sequentially affects the characteristics of the particle dispersion.2. The dispersion characteristics of the granular jet in the parallel-nozzle and cross-nozzle are analyzed. The dispersion modes in the parallel-nozzle are also analyzed. The calculational formula of the undistured length is obtained by analyzing the force acting on the particles. An entrainment model is used to calculate the dispersion length and the model successfully predicts the dispersion length. The minimum diameter of granular jet and its appearing-position are obtained by analyzing the granular jet in cross air jet and their calculational formulas are also obtained. It is found that the Strouhal number, Sth, can be used to distinguish the dispersion modes of the granular jet, when0.07> Sth>0.03, it belongs to the wave dispersion mode, when0.02> Sth>0.01, it belongs to the oscillating mode, and when0.03> Sth>0.02, it belongs to the transition state between the wave dispersion and the oscillating dispersion.3. The dispersion of the particles is invesgated by the numerical simulation. The Realizable k-ε model is used to model turbulence. The discrete particle method is employed to track particle motion and the probability-collision is used to consider the inter-particle collision. The results show that the axial velocity of air increses with the increase of the cross angle and will increase to a max value. The turbulent kinetic energy is highest on the interface between granular flow and air flow, which is in favor of the particle dispersion. The particle concentration decreases along the axial direction as a whole, and its profile agree with the Gauss function in the radial direction. The collision among particles is the most intense on the interface of the granular jet.4. A2D LES-DPM (large eddy simulation-discrete particle method) is developed to take account the dispersion modes of the granular jet in a parallel coaxial air. The void fraction and the iner-particle collision is introduced into the Fluent through re-organize the gas phase equations in Fluent. The global features of the flow field are obtained. It is found that there is invese flow between the air jet and granular jet near the nozzle, which would make the particles take off the interface of the granular jet and then wear the nozzle. The air velocity, particle velocity, particle concentration and the frequency of the collision between particles are also obtained. It is found that the above characteristics can reflect the state of the dispersion of the granular jet. By analyzing the interaction between air and particles (including the no linear of the drag coefficient and the operating pressure) and the inter-particle collision (or transmission of the energy between particles), the mechanics of the dispersion of the granular jet is investigated. The results suggest that both of the two interactions are important for the dispersion modes, and the nolinear of the drag cofficicent is dominant.更多还原