旋风分离器内颗粒质量浓度分布数值模拟

采用颗粒随机轨道模型和单元内颗粒源法,对旋风分离器内不同粒径颗粒质量浓度分布进行了数值模拟。结果表明,粒径较小的颗粒(dp≤4μm)大部分在旋风分离器分离空间锥段进行分离,而较大颗粒(dp>4μm)大部分在环形空间与分离空间筒段即被分离。随着颗粒粒径增加,分离器外壁的颗粒质量浓度逐渐呈螺旋灰带分布,内旋流夹带减小,环形空间顶板下方出现顶灰环。升气管入口0.25D(筒体直径)附近的短路流对小颗粒的影响较大。在分离空间下部排尘口附近0.5D有明显的颗粒返混,返混量随着颗粒粒径增大而减少。     

转笼式选粉机的流场模拟分析

利用美国ANSYS公司workbench环境下CFX软件对选粉机内部流场进行了模拟分析,结果直观地印证了选粉机的理论研究成果;文章还就选粉机转子内部有无涡流消除叶片模拟结果进行了分析比较,得出结论与理论相符.     

带导流叶片的JLX型旋风分离器数值模拟研究

为了确保IGCC燃气轮机长时间平稳运行,IGCC粗煤气需要在进入燃气轮机前将气流中携带的尘粒脱除。文中针对IGCC特定的工艺条件,开发了一种新的JLX型径向进口旋风分离器,并采用Fluent软件进行了数值模拟,研究了相关参数对分离器性能的影响。结果表明:螺旋导流叶片可有效改善流场分布,并实现对粉尘颗粒的预分离;随着导流叶片旋转圈数的增加,压力损失和切向速度随之增加,粒级效率先增加后趋于平缓,1.5圈为最优旋转圈数;随着导流叶片螺旋倾角的增加,环形空间切向速度和压力损失也随之减小,而较小的导流叶片螺旋倾角对提高粒径大于7μm的粉尘颗粒粒级效率是有利的。     

环流式旋风除尘器内颗粒运动的数值模拟

采用CFD软件Fluent提供的雷诺应力模型（RSM）和随机轨道模型,对环流式旋风除尘器内颗粒运动轨迹进行了数值模拟研究。预测了不同粒径颗粒的运动轨迹和分离效率。结果表明：颗粒在环流式旋风除尘器内的运动路径比常规除尘器长;特殊的流路设计,避免了常规旋风除尘器易产生的上灰环和颗粒短路问题,使除尘效率大幅度提高;除尘器内颗粒运动有较强的随机性,尤其对于小颗粒,受气流湍动影响显著。对不同粒径颗粒分离效率的预测表明：环流式旋风除尘器的分割粒径为1．25μm。     

旋转型分离器流场中粒子运动的数值解析

作为固液分离器的基础研究,应用龙格-库塔法对进入旋转态液体中的固体粒子由运动开始到被分离完成的全过程进行了数值计算。动力学模型中除考虑了重力、浮力、流体粘性力外,还考虑了假想质量力、Basst力、Sffm an扬力以及压力梯度力等多种力的作用。在实验装置中与数值计算参数相同的条件下进行了可视化实验研究。计算结果发现,在运动开始阶段,粒子的粒径越小,加速度越大,很快进入运动平衡状态,相反粒子粒径越大,加速度越小。运动的第2阶段,直径大的粒子仍在加速运动,因此不同直径的粒子运动之间存在一个运动加速度、速度及位移逆转现象。数值解析结果与可视化实验结果进行了比较,证明了数学模型与计算结果的正确性。     

Numerical simulation of salt water electrolysis in parallel-plate electrode channel under forced convection

A steady-state numerical model for multi-ion parallel-plate electrode (PPE) system is developed to investigate the concentration and electric distribution in the process of salt water electrolysis under forced convection. The finite-element method is used to solve this multi-ion transport model coupled with ionic diffusion, convection and ionic migration. The flow field and the electrode current's effect on the concentration distribution are investigated. The comparison between the diffusion-transported current and the migration-transported current demonstrates that the current is almost fully transported by the ionic migration, with the result that the diffusion-transported current can be neglected and the control equation of potential is simplified. For comparison, a hypothetical model with uncoupled situation of concentration and electric field is taken into consideration. The variation of electric field strength near the cathode can reach 25% of the value of the uncoupled model in the condition of u₀ = 0.01 m/s. Compared with this, the variation of ionic electro-conductivity shows a reverse tendency.     

双循环旋风分离器除尘机理的数值模拟

双循环旋风分离器通过将主进口设置在筒体中部,将顶部进气口设置为回流口,消除了进气口附近的二次流,避免了短路流,将大于3μm颗粒的分离效率提高至接近100%,并避免了少量11—15μm颗粒的短路逃逸。为了探索该设备的除尘机理,借助CFD软件,通过数值模拟研究的方式,辅助分析了2种进气口在分离性能上不同,传统旋风分离器不能完全分离3—8μm和11—15μm颗粒的机理,以及消除二次流的方法。计算结果表明:当回流气速低于主进气速时,会产生类似于顶端进气口的现象,即二次流、灰环和短路流,降低了小于6μm颗粒的分离效率。当回流气速略大于主进气速时,可以完全消除主进气口附近的二次流,使得所有粒径颗粒的分离效率都较高。模拟结果与实验结果从定性的角度符合较好。     

Numerical simulation of gas-solid flow in the axisymmetric inlets square separator

Numerical simulation was used to research the two-phase flow in the axisymmetric inlet square separator, including the basic flow characteristics, separation efficiency and comparing the difference between single-inlet and double-inlet separator. The effect of the reflecting cone’s geometrical sizes on pressure loss and efficiency was discussed. And the wall erosion condition because of solid particle impingement was calculated and analyzed. The tangential inlet diffuse square separator using RSM modeling that considers anisotropic situation was researched. The distribution of axial, tangential and radial velocity and the pressure loss calculated were analyzed. The results show that there is the typical double deck flow structure in the separator, the square section influences the tangential velocity in the corner, the pressure distribution divides in the inlet on the reflecting cone, and the pressure loss increases with the increase of inlet velocity. This work was presented at the 7 ^th China-Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.     

太阳能固体颗粒吸热器数值模拟研究

太阳能固体颗粒吸热器是一种利用自由下落的固体颗粒来吸收聚焦太阳辐射的吸热器。考虑了颗粒相与流场之间的相互作用以及颗粒相对辐射场的影响,基于离散相模型和DO辐射换热模型,对固体颗粒吸热器中幕状物的形态以及吸热性能进行了数值模拟,讨论了辐射强度、颗粒直径、颗粒质量流率、颗粒吸收率和颗粒初温对固体颗粒吸收器的流场和热性能的影响规律。模拟结果表明:颗粒质量流量和颗粒粒径对吸热器效率的影响明显;入射辐射强度从500 kW/m~2增加到1 500 kW/m~2时,颗粒出口温度提高,吸热器效率从46.51%逐步增加到49.74%;颗粒粒径从1 297μm减小到500μm时,吸热器效率由35.5%增加到52.1%;颗粒质量流量从1.2 kg/s增加到6.7 kg/s时,颗粒出口温度降低,吸热器效率从23.8%增加到57.6%;颗粒初温由300 K升高到900 K时,颗粒温升降低,吸热器的效率从42.2%下降到37.9%。     

Applications of the four-parameter distribution to electrostatic charge and particle size distribution

A four-parameter model has been developed to describe the size and charge distribution of aerosols. In the limiting case the distribution reduces to a log-normal distribution for the particle size and a normal distribution for the particle charge.A procedure for systematically determining the distribution is presented. Finally, applications of the distribution to model the optical diameter of asbestos fibers, the bimodal charge distribution of NaCl aerosols, and atmospheric aerosol size distributions are presented.     

Numerical simulation of effect of inlet configuration on square cyclone separator performance

This paper presents a numerical study of the gas-solid flow in square cyclone separators with three types of inlet configuration. Three-dimensional Reynolds Stress Model (RSM) was used to simulate the turbulent flow of gas phase and a Lagrangian equation was used to simulate the particle motion. The resulting velocity, separation efficiency and pressure drops were verified by comparison with measured data. The effect of inlet configurations on the turbulent dynamics in the cyclone and the separation efficiency and pressure drop was analyzed. Results showed that inlet configurations influenced the turbulent dynamics in the cyclone and led to different pressure drop and separation efficiency. The separator with double declining inlets (DDI) had the minimum pressure drop and similar efficiency to the separator with double normal inlets (DNI). The separator with single normal inlet (SNI) had the best separation efficiency and the maximum pressure drop. When a baffle was installed in the inlet of separator SNI, the pressure drop increased by about 191% and 34% for the separator with a straight (SNI-1) and curved (SNI-2) baffle respectively on the basis of the pressure drop of separator SNI. The cut and critical diameter of particles were 2 μm and 14 μm for separator SNI-1 and 4 μm and 14 μm for separator SNI-2, while they were 8 μm and 30 μm for separator SNI at the same inlet conditions.     

蒸汽凝结促进多分散不可溶PM_(2.5)增长的数值模拟

以PM2.5为凝结核,发生蒸汽凝结能够使得PM2.5粒径增加,以利于后续脱除。了解PM2.5的凝结增长规律对于PM2.5的高效脱除有重要意义。为此,基于凝结增长动力学方程,研究等温和绝热系统中多分散不可溶PM2.5的凝结增长过程,探讨蒸汽凝结后颗粒粒径分布随时间、蒸汽饱和度、温度的变化规律,并将等温和绝热系统中颗粒的凝结增长特性进行对比分析。结果表明,过饱和蒸汽能够迅速在PM2.5表面发生凝结,促进颗粒粒径分布向着大粒径、窄分布的方向发展;相同初始温度条件下,提高蒸汽饱和度可以有效促进PM2.5的增长;相同初始含湿量条件下,温度的较小变化就会引起最终颗粒粒径分布发生显著变化,且温度越低,颗粒凝结增长效果越好;与绝热系统相比,相同初始条件下等温系统中凝结增长所需的时间更长,生成的最终颗粒也更大。     

PM10和PM2.5的危害及控制对策

PM10和PM2.5不止会降低环境质量,还会对人体产生巨大危害,直接威胁着人类健康。所以,如果不对此加以控制,人类的生存条件将迅速恶化,产生的后果是极为可怕的。为了减轻PM10和PM2.5对环境、人体的危害,相关部门必须尽快采取强有力的管理措施,遏制环境问题进一步恶化的趋势。文章从PM10和PM2.5造成的危害出发,提出了几项控制建议。     

旋风分离器内颗粒运动规律的数值模拟

采用单颗粒动力学模型计算了旋风分离器内颗粒的运动轨迹。计算结果表明：进入旋风分离器的颗粒绝大多数在环形空间内就被甩向器壁；从入口上部进入的部分较小颗粒由于局部二次流作用而上升形成顶灰环；还有少量颗粒进入下部分离空间。在下部分离空间内，有灰斗返气夹带上来的颗粒，处于内旋流的颗粒则有可能随上升气流而逃逸，所以一定的分离空间高度有利用颗粒的二次再分离。     

Numerical simulation of particle breakage in dry impact pulverizer

A novel method to simultaneously simulate particle motion and its breakage in a dry impact pulverizer was developed. The motion of particles in the pulverizer was calculated using a discrete phase model (DPM)‐computational fluid dynamics (CFD) coupling model. When the particle impacts against a vessel wall, impact stress acting on the particle is calculated from Hertz's theory as a function of the impact velocity. At the same time, the particle strength as a function of the particle size is calculated from Griffith's theory. If the impact stress is larger than the particle strength, the particle is broken and replaced with smaller fragments. The size distribution of the fragments is obtained from a breakage function proposed. The motion of the fragments is calculated again by using the DPM‐CFD coupling model. By repeating the above calculations over the whole particles, the grinding phenomenon can be simulated. The calculated results showed good agreement with the experimental one, and validity of the proposed method was confirmed. © 2013 American Institute of Chemical Engineers AIChE J, 59: 3601–3611, 2013     

Numerical simulation of particle motion in vibrated fluidized beds

Flow behavior of particles is simulated in a two-dimensional vibrated bubbling fluidized bed. The motion of particles is simulated by discrete element method (DEM). The distributions of velocity and concentration of particles are analyzed at the different amplitudes and frequencies of vibration. In the case with vertical vibration, the bed consists of three different regimes along bed height: a low particle concentration regime with a vibration gap near the bottom, a high concentration regime in the middle of the bed and a transition regime at the bed surface. The gas pressure losses are reduced with the vibration. The phase delay time between the time at the maximum pressure loss and the time at the maximum displacement of vibrated distributor in one cycle decreases with the increase of amplitudes. The contacting interaction between the vibrated distributor and particles increases as the distributor moves up, and trends to zero as the distributor moves down with the increase of frequency of vibration. The vibrating energy is transferred by collisions between the vibrated distributor and particles at the period of acceleration of the distributor.     

Numerical simulation of in-flight particle oxidation during thermal spraying

Metal powders are widely used for thermal spray coating to improve wear, corrosion and temperature resistance of products. The high thermal profiles endured for sprayed particles give rise to oxidation on the surface of metal powders. Metallic oxides are brittle and undermine the performance of coated products. To understand the growth of oxide layers on in-flight metal powders, an oxidation model is implemented into the Lagrangian formula of particle tracking. The numerical simulation is achieved for a 3D combusting gas flow generated by a high velocity oxygen fuel (HVOF) thermal spray gun. The results are able to demonstrate the correlation between in-flight particle oxidation and operation parameters.     

Numerical simulation of particle motion in vibrated fluidized bed

The particle motion in vibrated fluidized bed was examined by using numerical simulation. A two-dimensional fluidized bed was used, and discrete element method (DEM) was used as for calculating the particle motion in vibrated fluidized bed. Geldart group B particle, which is regarded to have no effect of agglomerate, was used as the fluidizing particle. The vibration directions (vertical and horizontal) and vibration parameters (frequency and amplitude of vibration) were changed.In the case with vertical vibration, large bubbles caused by vibration gap (defined as the gap between particle bed and wall caused by vibration) appear in bed. When the vibration strength is high and the vibration frequency is low, it is difficult to fludize the particle bed in the case with horizontal vibration because the vibration gap acts like the channel. When the vibration frequency increases at the same vibration strength, the effect of vibration on the particle motion becomes small. The effect of vibration on the pressure loss in particle bed is large in the case with horizontal vibration.     

排气管尺寸对旋风分离器流场影响的数值模拟

用雷诺应力湍流模型（RSM）模拟研究旋风分离器排气管尺寸对旋风分离器流场的影响.结果表明：单入口旋风分离器的非轴对称性在环区更明显;在排气管壁存在滞流区,排气管尺寸减小,该滞流区变薄;在分离区,De/D≥0.4时,旋风分离器的中心位置存在向下旋流,该旋流造成一定返混,对提高旋风分离器效率不利;随着De/D的减小,内旋流切向速度提高,中心处的向下旋流速度减小,总压降大幅提高;当De/D=0.3时,中心处向下旋流消失,提高了分离效率.