非等温液-液对置撞击面温度分布均匀性

对不同条件下非等温过程液-液对置撞击后形成的气液混合撞击面的温度分布均匀性进行了研究。以温度不均匀系数和撞击面温度分布作为评价标准,利用Mixture模型数值模拟撞击过程,并基于平面激光诱导荧光（PLIF）技术进行可视化测量实验验证计算模型。通过对不同的喷嘴出口速度（v）、喷嘴对置间距（L）以及湍动能等条件下撞击面温度分布进行研究。结果表明,喷嘴直径和喷嘴对置间距一定时,增加喷嘴的出口流速,则温度不均匀系数整体呈下降趋势;喷嘴直径和喷嘴出口流速一定时,非等温液-液对置撞击后形成区域温度场分布随喷嘴间距的增加,其温度分布区间呈减小趋势。L=3D时,温度的分布区间最小,温度场分布最均匀。湍动能的分布曲线越平稳,液-液对置撞击后形成的气液混合撞击面的温度分布越均匀。     

双出口旋风除尘器压损和分离效率的模拟研究

通过对新型双出口旋风除尘器在不同风量、不同粒径大小等条件下进行数值模拟分析,研究结果表明：双出口旋风除尘器进口风量越大,系统的流速越大,旋风除尘器的压差也越大,压力损失主要集中在旋风除尘器的入口至蜗壳处、除尘器上部以及旋切叶片与出风口连接处,当入口风速为13.21m/s时旋风除尘器压损为375Pa,当入口风速增加至26.42m/s时旋风除尘器压损为1 572Pa,即入口的风速增加一倍,旋风筒的压损增加三倍左右;双出口旋风筒入口流速与收尘效率呈正相关,入口流速越大,内部分离效率越高,收尘效率也越高,但阻力也随之增大,因此入口流速的选择应平衡效率和阻力的关系;粉尘颗粒粒径越大,越容易被捕集,当粉尘粒径<5μm时,很难被双出口旋风除尘器完全捕集下来。     

多床层径向反应器中床层的流场行为

在直径3m、高5m的大型多床层径向反应器冷模装置上,通过测定流体在流道和各分床层内的静压分布,考察了各分床层的流体流动行为和特征.结果表明,当流道静压差的均方根偏差小于1%时,各分床层静压差的均方根偏差小于5%,流体在各分床层的径向流速沿轴向分布均匀,流速最大偏差小于5%;当流道静压差沿轴向的差别大于10%时,则其沿轴向分布显著不均匀,且靠近流道静压变化梯度大的分床层的径向流速均匀性最差,床层上下端流速偏差达70%.Π型流动形式是动量交换型径向反应器的最佳选择,适宜的两流道静压差设计可实现径向流速沿床层轴向完全均匀分布。     

关于回收型风筒若干问题的探讨

<正> 一前言近几年来我国大中型机力抽风冷却塔中出现了一些新的风机或部件,椭园型风筒即为一例。这种新筒型的出现,不仅改进了传统塔的塔型,精减了某些专门导流装置,而且它和L47风机相辅相呈,也改变了传统塔的风机和塔体工作不协调状况。例如,它和L47风机配套时,可提高L47的某些性能,并充分满足该国家优质品的使用条件。再如,化工部“L47型风机逆流式冷却塔通用图”中的塔型,较传统塔型有所变化,主要由新筒型引起的。就该风筒(包括基础)型线而论,和椭园型风筒基本一致的。     

板翅式换热器封头结构物流分配的PIV实验研究

在数值模拟的基础上,利用粒子图像测速仪(PIV)对板翅式换热器原始封头A和3种改进的顺排孔板型封头结构(B、C、D)的流场进行了可视化的实验,获得了封头内部不同截面处流场的速度流线分布图.比较了Re＝6.22×10⁴时原始封头A和一种改进型封头B的出口物流分配以及3种不同中孔面积比率的改进型封头对出口物流分配的影响.结果表明：改进型封头结构能有效地改善物流分配的均匀性;C型封头的不均匀参数S_U和最大流速与最小流速之比θ_U最低;流量分布和中孔面积比率之间存在着一个最佳值.     

撞击流反应器撞击区流动特性研究

为研究撞击区的流动特性,在有效容积为160 L的撞击流反应器内,以水为介质,饱和KCl溶液为示踪剂,用电导法测定了不同导流筒出口间距和撞击流速下的示踪剂浓度曲线,并通过多釜串联模型拟合得到了撞击区的平均停留时间及模拟釜数。结果表明:导流筒出口间距减小,撞击流速增大,撞击区平均停留时间减小,釜数减小;撞击流速为2.0 m/s时,撞击区内流型接近于全混流。停留时间分布主要受撞击流速的影响,增大流速有利于促进撞击区中的宏观混合。     

椭圆度与材料不均匀性对外压容器临界压力的影响

在容器制造或使用过程中会引起椭圆度与材料不均匀性几何缺陷。利用有限元分析软件ANSYS中两种分析方法初步探究椭圆度和材料不均匀性对失稳时容器临界压力的影响。结果表明:存在椭圆度的外压筒体的临界压力随椭圆度的增加而降低,导致筒体承载能力下降,使失稳提前发生;由材料不均性引起几何缺陷也会对外压容器临界压力产生一定的影响。     

基于粒子图像测速技术的流浆箱阶梯扩散器性能试验

采用粒子图像测速(PIV)系统对两种出口段型式阶梯扩散器的内流场进行了测试,得到了多种流量工况下阶梯扩散器轴向水平截面的速度分布、阻力损失及阶扩处空化等情况。测试结果表明,入口浆速为8～24m.s-1时,出口段横向速度分布在长径比为3～5时达到均匀,随后圆管出口段横向速度分布再由均匀发展到不均匀,而方管出口段的横向速度在达到均布后,后续流动没有明显不均匀的横向速度分布。入口浆速越大,对纤维的解絮越有利,但随着入口浆速的增大,流动阻力急剧增加,阶扩处空化区域增大,故在纤维充分分散的前提下,入口浆速以不超过空化的临界浆速为宜。研究表明,方管出口阶梯扩散器更适用于高速纸机,适当高的浆速和合适的形状尺寸是获得定量均匀、匀度好纸张的保证。     

宣钢旋流顶燃式热风炉传输现象的研究

针对宣钢旋流顶燃式热风炉的燃烧室,建立了气体流动、传热及燃烧的数学模型,通过数值模拟研究了燃烧室的流场、温度场和CO浓度场.结果表明,热风炉燃烧室出口速度和温度分布很不均匀;由于空气过剩系数过低,导致燃烧室出口有6%的CO剩余,火焰贴近燃烧室壁面,严重影响热风炉的寿命.将空气过剩系数增加到1.05后比较发现,燃烧室出口CO质量分数低于1%,火焰分布更加合理,增加燃烧室高度能有效提高燃烧室出口速度和温度的分布均匀性,速度最大差由10m/s降到约2m/s,温度最大差由140℃降到约90℃.     

基于CFD数值模拟的换热器管箱内流场分析

管壳式换热器进口管箱中流场分布对换热器的换热效率和管子与管板连接处的泄露失效有着重要的影响。本文设计了三种不同半锥角的开式导流筒,采用CFD数值模拟方法,以流场和压力场的均匀性作为衡量指标,研究了不同导流结构和普通管板上流场和压力场的分布。根据模拟结果可以看出,导流筒能较好地改善管箱管板上的流场和压力场分布,其中半锥角为60°的导流筒流场均匀性最好,压力分布也比较均匀,但半锥角对压力分布影响不大。研究结果对管箱内导流筒的选型和设计具有一定的指导意义。     

KINETIC THEORY OF FLOW IN STRONGLY INHOMOGENEOUS FLUIDS

Enskog's kinetic theory of dense hard sphere fluids, modified to allow long-ranged attractive interactions in a mean field sense, is solved for the case of slow flow in strongly inhomogeneous fluids, such as fluids near solid surfaces or liquid-vapor interfaces. In the equilibrium limit the theory yields the exact Yvon-Born-Green equation for the density distribution. In the slow flow limit the viscosity is a tensorial functional of the density distribution. Expressions for the velocity profile are derived for plane laminar and Couette flows. The density dependence of the transport coefficients is smoothed once through the angle averaging of the binary collisions of the Enskog theory. In the planar flows the velocity profile obeys a second order differential equation with variable coefficients and so the density dependence is further muted by two successive spatial integrations. The result leads one to expect the velocity profile to depend relatively weakly on density variations. This conclusion is in agreement with recently available computer simulations of flow in micropores. Another conclusion of the work is that one cannot introduce a flow or pore size independent effective viscosity to describe flow in micropores.     

CFD simulation and experiments of dynamic parameters in gas–solid fluidized bed

Particle and bubble motion plays an important role in determining the hydrodynamic characteristics of a fluidized system. The dynamic parameters of a fluidized bed are reflection of the complex correlation between particle–particle and particle–bubble in a system. A two-dimensional Eulerian–Eulerian model integrating the kinetic theory of granular flow is used to simulate the bubble and linear low density polyethylene (LLDPE) particle dynamic behavior in a gas–solid fluidized bed. The simulated method is validated by pressure fluctuation experiment. The computed vertical turbulent energy spectrum of particles is applied to identify the particle motion intensity and the inhomogeneity of turbulent energy dissipation. The energy spectrum captures the Levy–Kolmogorov law in inertial range at high frequency. Furthermore, the flatness factors of wavelet decomposition coefficients of particle fluctuation velocity are for the first time introduced to analyze the intermittence caused by coherent structures in the flow field. The results show that the intermittence in dissipation range is much stronger than that in energy-containing and inertial range, and reinforces rapidly as the radial distance and the bed height increase. Moreover, the acoustic emission (AE) energy is found to be able to indicate the flow regimes. By combing granular temperature and AE energy, the relationship between the spatial distribution of granular temperature and the flow regimes is established. To get more detail of bubble motion behavior, the power spectrum of voidage fluctuation is analyzed. This work provides valuable insights into the dynamic characteristics and the flow field information of a gas–solid fluidized bed by CFD simulation.     

立体传质塔板罩内的气相速度分布

罩内气速分布是反映立体传质塔板帽罩结构合理与否的重要参数。文中在600 mm的冷模实验塔内采用热膜测速仪对立体传质塔板(CTST)帽罩内气体速度分布进行了实验研究,发现气体在CTST帽罩内的流动形态大致可以分为3个阶段,即回旋区、发展区、喷射区。各区域内的气速分布特点显著不同,分别起到不同的作用。不同板孔气速条件下,各区域速度分布的变化趋势基本一致。罩内气速分布与压力分布的对比情况较好地反映了罩内动能与势能之间的能量转换规律。     

Numerical simulation of fiber orientation distribution in round turbulent jet of fiber suspension

The Reynolds averaged Navier–Stokes equation was solved numerically with the Reynolds stress model to get the mean fluid velocity and the turbulent kinetic energy in a round turbulent jet of fiber suspension. The fluctuating fluid velocity was described as a Fourier series with random coefficients. Then the slender-body theory was used to calculate the fiber orientation distribution and orientation tensor. Numerical results of mean axial velocity and turbulent shear stress along the lateral direction were validated by comparing with the experimental ones. The results show that most fibers are aligned with the flow direction as they go downstream, and fibers are more aligned with the flow direction within the region near the jet core. The fibers with high aspect ratio tend much easier to align with the flow direction, and the fiber orientation distribution is not sensitive to fiber aspect ratio when fiber aspect ratio is larger than 5. Fiber density has no obvious influence on the fiber orientation distribution and fiber orientation tensor. The randomizing effect of turbulence is insignificant in the regions near outside and jet core, and becomes significant in the region between outside and jet core. The randomizing effect increases with the increasing of the distance from the jet exit. Different components of fiber orientation tensor show a similar distribution pattern.     

Fibre orientation distribution in turbulent fibre suspensions flowing through an axisymmetric contraction

The Reynolds averaged Navier–Stokes equation was solved numerically with the Reynolds stress model to get the mean fluid velocity and the turbulent kinetic energy in turbulent fibre suspensions flowing through an axisymmetric contraction. The fluctuating fluid velocity was represented as a Fourier series with random coefficients. Then the slender‐body theory was used to predict the fibre orientation distribution and orientation tensor. Some numerical results are compared with the experimental ones in the turbulent fibre suspensions flowing through a contraction with a rectangular cross‐section. The results show that the fibres with high aspect ratio tend to align its principal axis with the flow direction much easier. High contraction ratio makes the fibre alignment with the flow direction much easier. The contraction ratio has a strong effect on the fibre orientation distribution. Only a small part of the fibre is aligned with the flow direction in the inlet region, while most fibres are aligned with the flow direction when they approach to exit. The fibres are aligned with the flow direction rapidly in the inlet region, after that the fibre orientations change little in the most of the downstream region. The fibres with high aspect ratio are aligned with the flow direction faster when they enter the contraction. The randomising effect of the turbulence becomes significant in the downstream region because of the high turbulent intensity.     

小间距两喷嘴对置撞击流流场的数值模拟与实验研究

运用热线风速仪和CFD软件对小喷嘴间距下两喷嘴对置撞击流时均流场进行了实验研究和数值模拟，并和文献中的实验结果和近似解析式进行了比较。研究结果表明：由于边界层存在，单股喷嘴出口速度分布为“礼帽”形状分布；在L<2D(L为喷嘴间距，D为喷嘴直径)时，喷嘴出口速度剖面出现中间低、两边高的“双峰”形状， L=2D时，“双峰”形状消失。随着喷嘴间距的增大，相同气速比导致的撞击面驻点的偏移量增大。相同气速比下，喷嘴出口为“礼帽”分布时驻点的偏移量比均匀分布时大。文献中的撞击流流场的近似解析式对喷嘴出口速度分布为均匀分布有很好的精度，当喷嘴出口速度为“礼帽”分布时，文献中近似解析式的预报精度变差。     

The efficiency of the particle acceleration in a jet pipe

In jet-mills the grinding material is accelerated in a jet pipe by means of expanding gas. The invested energy cannot be completely converted into kinetic energy of the particles because there are energy losses caused by wall friction, the slip between gas and particles, and the unconsumed kinetic energy of the gas at the pipe exit. The efficiency is defined as the ratio of the kinetic energy of the particles at the exit of the pipe and the total applied energy. With an assumption about the velocity distribution in the pipe, a formula is derived for the velocity ratio at the end of the pipe. This ratio, the load, and the geometrical sizes of the pipe influence the efficiency of the particle acceleration.     

加料速度对分级机内部流场的影响

用Fluent软件模拟仿真分析了FTW型涡轮空气分级机内部流场的动态压力、湍动能、流动速度的分布, 对比分析不同加料速度对分级机内部流场的影响。结果表明:加料速度增加, 动态压力降低, 但分布曲线的对称性更好;湍动能降低, 但分布更为均匀;径向速度增加, 切向速度和轴向速度都降低, 且分布更为均匀, 其中轴向速度较大, 对流场影响更大;有利于流场稳定, 更有利于物料分级。实验测试了分级粒径分布部分支持这些效果。     

滚筒端面对颗粒物料轴向流动特性影响的离散模拟研究

针对碎渣工艺中仅一个端面可随侧壁转动的短滚筒体系，采用离散单元法模拟研究了滚筒轴径比和转动速度对颗粒物料轴向流动特性的影响。模拟结果表明，系统内形成了显著的轴向对流结构：物料层顶部处颗粒物料会朝向滚筒固定端面一侧运动，而物料层趾部区域颗粒则朝向滚筒转动端面一侧运动。低转速条件下，沿物料自由表面由顶部到趾部，颗粒轴向速度呈非对称分布，顶部区域颗粒轴向速度绝对值显著小于趾部区域颗粒轴向速度绝对值；两部分区域颗粒轴向速度绝对值分别在y/R=±0.725处达到极大值，且轴向速度为0的位置并不出现在切向的中间位置。改变滚筒的轴长对这种非对称分布的影响近似可忽略，但是增大滚筒转速会增大颗粒轴向运动速度并逐步减弱这种非对称性。改变滚筒转速，对物料顶部区域颗粒的轴向流动的影响要大于对趾部区域颗粒轴向流动的影响。当滚筒轴径比达到1.2后，滚筒转动端面对物料轴向流动的影响区域不会随滚筒转速的增大而呈现显著变化。这些结果为实际滚筒碎渣工艺的结构优化提供了理论指导。     

分层填料对旋转填料床气相流场影响的数值模拟

通过设计简化的分层填料旋转床(SP-RPB)模型，采用计算流体力学方法(CFD)对比同尺寸旋转填料床(RPB)的稳态气相流场。分析转速和进料速度对气相压力、相对速度及湍动能分布的影响，同时还考察了单位丝网圈上的压降情况。结果表明，在气体进入各级填料位置的相对速度出现峰值，湍动能分布与之相同，各峰的出现位置仅由填料位置决定，两者共同表明SP-RPB具有多个端效应区域。转速增加对相对速度峰值大小有更明显的提升，较大的进料速度使填料内气体的速度波动更大，也使湍动能的峰值有所增加。由于SP-RPB内填料厚度较RPB变薄，从整个设备范围上看，SP-RPB表现出更低的压降。进气速度提高和转速降低使SP-RPB两层填料间的高压范围变窄，但SP-RPB的单位丝网圈数压降更大。