近壁面静止圆球的尾迹特性

圆球在大空间均匀来流下的绕流特性已得到了广泛的研究,但是壁面对圆球绕流特性的影响还未清楚。通过实验方法研究了与壁面接触的静止圆球在明渠流中的绕流特性,重点关注了圆球后尾迹的特性。研究发现,圆球尾迹存在三种状态：稳定状态、非稳定对称状态和非稳定非对称状态。当Re<150时,尾迹呈稳定状态,尾迹关于垂直于壁面的平面对称;当150<Re<400时,尾迹呈对称状态,Reynolds数较高时,圆球后存在规则的、周期性的涡脱落,Strouhal 数为0.26~0.33,脱落涡关于垂直于壁面的平面对称,此时尾迹功率谱的频带分布较宽;而当Re>400时,圆球后的涡脱落不再对称,尾迹随着Reynolds数的增大呈现混沌特征。     

不连续扰流板强化搅拌的模拟仿真及机理分析

基于传统的四挡板搅拌槽,添加了不连续扰流板,并对其进行了非对称布置。采用数值模拟方法,对比研究了无不连续扰流板、不连续扰流板对称布置和两种不连续扰流板非对称布置的四挡板搅拌槽内的流场特性和混沌效果。结果表明,在功率准数不变的情况下,不连续扰流板会抑制周期性的流体径向和切向流动,下降幅度分别为42.19%和19.55%,增强传质作用更强的轴向流动,增幅为20.27%,破坏流体运动的周期性,引起宏观流场的整体流型增加了大量拉伸折叠的随机迹线变化,令示踪流体发散至周围区域,不连续扰流板附近区域呈现混沌特性,混合效果提高;一对和两对处于相对位置的不连续扰流板上下布置时的最大速度差相较于对称布置时的分别提高472.72%和218.18%,这种速度场分布的不均匀,大大增加了流体微团碰撞概率,整体搅拌区域趋于混沌,搅拌过程被强化;将其应用于硫酸锌净化过程,结果表明,非对称布置扰流板打破了槽内的周期性拟序结构,引起多尺度涡旋产生,让能量耗散于杂质离子和锌粉粒子之间的碰撞,提高了置换反应速率,整个过程节约能量14.3%。     

Sphere flattening with application to the moderate plastic compaction of regular sphere assemblages

The problem of flattening a rigid/perfectly plastic sphere under a uniaxial compressive loading is solved. This solution gives approximate relations between contact force and contact area analogous to the Hertz classical solution for an elastic sphere. It is used as the basis for studying the moderate plastic compaction of arrays of spheres. The simple cubic and hexagonal close-packed arrangements, representing the extremes of initial density, are treated for various deformation conditions. Pressure—porosity expressions are derived and are used in several comparisons with available experimental data. The theory shows, as expected, that the work required to achieve a given compressive strain is less in the simple cubic arrangement than in the hexagonal close-packed arrangement, and less for uniaxial compression than for biaxial or triaxial compression.     

内置阻块型微混合器内流体混合强化的数值模拟

采用计算流体力学方法对3种内置阻块波浪形微混合器进行模拟研究,考察内置阻块尺寸、排列方式及阻块数量对流体混合的强化效果。由速度场和物质输运模型结合进行流体的混合模拟,得到流体混合快照图和流体混合速率,进一步由流体平均径向线拉伸和李雅普洛夫指数定量表征混沌混合程度。结果表明:混合器壁面波浪状V形凹槽的设计和微通道内长方块的设置产生周期性的流场,从而引发混沌流。将阻块倾斜设置或增加微通道内阻块的数量,混沌流作用增强,从而促进流体混合。最后考察了不同贝克来数Pe下流体的混合性能,发现微通道混合量纲一长度与lnPe之间呈线性关系。     

基于0-1测试的底吹搅拌混合过程混沌特性分析

通过建立水力学模型研究底吹搅拌混合过程,利用流场可视化技术与直接成像技术获取实验图像数据,引入0?1测试方法,考察了喷枪布置方式(个数与角度)对混合过程混沌特性的影响. 结果表明,基于颜色指示剂,利用数字图像处理手段可以近似估测混合过程的气含率,气含率演化规律符合实际工况运行特征;对各工况的气含率时间序列进行0?1测试,渐进增长率Kc中位数在一定程度上反映了不同混合过程的混沌强弱.     

Pitch coke structure and its transition into graphite: Influence of the separation process of quinoline-insoluble matter

It has been established that the texture of pitch coke depends on the pre-carbonization treatment of the pitch and the separation of the primary quinoline-insoluble matter (OI). Scanning electron microscopy was used to examine the texture of fracture surfaces of pitch cokes prepared from the raw pitch and from pitches deprived of their QI fractions by quinoline extraction or filtration, three basic structures, lamellar, globular and composite, being determined. The arrangement of the lamellar structure is affected by the method of separation of QI and results in different graphitizable products. In pitch, filtered at 350 °C, the first symptoms of lamellar arrangement were already observed at heat treatment $\text{1 > 450}\text{°C}$.     

Simulation of random packing of polydisperse particles

An optimization based model that simulates random packings of polydisperse particles to mimic porous media systems is presented in this paper. The model simulates systems with properties that map back to physically measured quantities. The model is composed of three main procedures: detachment of an existing sphere from a target sphere by moving its center to a new position, movement of an existing sphere to touch the target sphere, and addition of a new sphere to touch the target sphere. Each procedure is performed to satisfy a constrained nonlinear optimization formulation. Input parameters include radius and coordination numbers density functions. A monodisperse and polydisperse packings were simulated by incorporating physically based properties of glass bead packings obtained from 3D computed tomography images. In each simulated system, the packing density obtained was very close to the packing density of the physical system. The packings were tested for isotropy, homogeneity and randomness and then compared to experimental microtomography images. Findings indicate that the packings generated were isotropic, homogenous, random, and in a good agreement with the experimental data.     

Slip in Flow through Assemblages of Spherical Particles at Low to Moderate Reynolds Numbers

Effects of slip velocity and volume fraction of slip spheres on the momentum transfer characteristics of assemblages of slip spheres are numerically investigated. The fluid slip along the surface of the sphere is considered by Navier's linear slip model. The dimensionless governing continuity and momentum equations are solved using a semi‐implicit marker and cell method implemented on a staggered grid arrangement in spherical coordinates. The convection and viscous terms of momentum equations are discretized by means of the QUICK scheme and a second‐order central differencing scheme, respectively. The present numerical solver is benchmarked via grid independence and comparisons with the existing literature values. Results were obtained over a wide range of pertinent dimensionless numbers such as the Reynolds number, volume fraction of the dispersed phase, and dimensionless slip parameter.     

Mechanical Packing of Spherical Particles

An idealized experimental study of particle packing was made. Spherical metal shot of several discrete, narrow size ranges was efficiently packed in glass containers by mechanical vibration. Packing arrangements and the dynamic process of packing were studied visually. One-size spheres packed in an orthorhombic arrangement with a density 62.5% of theoretical density. Forming of high-density multicomponent packings was shown to require at least a sevenfold difference between sphere sizes of the individual components. A quaternary packing with a density 95.1% of theoretical density was formed from spheres with diameter ratios 1:7:38:316 and volume compositions 6.1:10.2:23.0:60.7%, respectively. Such packings could be poured from their glass containers, thus proving that effective mechanical packing is simply an efficient arrangement of spheres of prescribed sizes and proportions. The significance and utility of this work to the ceramic and other industries is discussed.     

Improving conversion and selectivity of catalytic reactions in bubbling gas–solid fluidized bed reactors by control of the nonlinear bubble dynamics

In this paper a model is presented that is a dynamic extension of the classic two-phase reactor models used to predict conversion and selectivity of fluidized reactors. The most important part of the model is a dynamic discrete bubble model that can correctly predict bubble sizes and also exhibits chaotic dynamics. This bubble model is based on the discrete bubble models presented by Clift and Grace [AIChE Symp. Ser. 66 (105) (1970) 14; 67 (116) (1971) 23; in: J.F. Davidson, R. Clift, D. Harrison (Eds.), Fluidization, Academic Press, London, 1985, p. 73] and Daw and Halow [AIChE Symp. Ser. 88 (289) (1992) 61]. The latter showed that this type of models can exhibit chaotic behavior. By application of an extended version of Pyragas' control algorithm [K. Pyragas, Phys. Lett. A 170 (1992) 421] the bubble dynamics can be changed from chaotic to periodic in a ‘flow'-regime in which the model otherwise would predict chaotic behavior. Pyragas' control algorithm is used to synchronize a chaotic system with one of its periodic solutions using a feedback control loop. This results in smaller bubbles, thus enhancing mass transfer of the reactant gas in the bubbles to the catalyst particles. The model is used to predict the effect of the changed bubble dynamics on a catalytic reaction of industrial importance, viz. the ammoxidation of propylene to acrilnitril (Sohio process). It is shown that both conversion and selectivity are appreciably enhanced.     

Werkstoffe,Maschinen und Geräte für die rationelle Verpackung

Materials, Machines and Equipment for Economical Packing The significance of packing technology in industrial economics is steadily increasing. The developments in this sphere are not only limited in the invention of desirable or improved materials, plants, machines and accessories but are also extended especially towards economical arrangement of the production line with the aim to reduce the costs. Innovations of universal applicability are dealt with, which are valuable for the factory practice permitting thereby an improvement of existing processes.     

Revisit the adhesive contact between a nanoscale rigid sphere and an elastic half-space: considering the effect of sphere size

The current paper revisits the adhesive contact between a rigid nanoscale sphere and an elastic half-space. Using analytical solution for traction and a modified numerical scheme, a new simulation is proposed. The adhesive contact is simulated faster and more easily than previous researches. The effect of sphere size is investigated. A modified spherical JKR model and spherical DMT model are proposed. The results are compared with spherical JKR, spherical DMT, and rigid sphere model. The load–approach and contact radius–load relations can be predicted by the modified spherical JKR model for sphere radius larger than 50?. Finally, approximation equations for pull-off force vs. Tabor parameter and jump-in distance vs. Tabor parameter are proposed.     

球形胶囊内约束熔化过程的LBM模拟

为了准确预测球形胶囊内部材料的相变性能,为后续相变微胶囊浆体的多尺度研究提供微观相变信息,采用格子Boltzmann方法（LBM）,引入浸入式移动边界处理方案,借鉴糊状区和热焓理论,构建了适于相变模拟的数值模型,模拟了球形胶囊内部固液相变过程,讨论了不同粒径尺度下熔化机制的区别。结果表明,利用LBM方法得到的预测结果与可视化实验数据吻合较好,清晰地呈现出球体上部温度热分层和下部液相强对流共存的特性。随着粒径尺度的不断减小,胶囊内部对流作用逐渐减弱,甚至当粒径小于3 mm时,其内部对流作用可忽略。     

基于二次型性能指标的不确定混沌系统最优控制器设计

研究具有不确定性并带有扰动的混沌控制系统。首先基于成熟线性理论中的二次型最优控制理论将扰动非线性的混沌系统模型转换为无扰动的等价线性系统模型,然后给出了针对伪线性系统的基于二次型性能指标的最优控制器设计方法。对Liu混沌系统的参数不确定性的仿真结果表明：控制品质有了较大的改善和提高。     

混沌流翅片的传热研究

混沌流可以在层流条件下强化传热这个现象已经被有些文献所证实。文中提出一种基于混沌流现象的翅片,通过对其流道内流动进行简化,得出其动力学符合Duffing方程。利用数值模拟手段,计算了在各种几何外形、不同入口流速、不同介质条件下的传热规律,回归出了在层流条件下,翅片的平均Nu准数表达式,即0.086Re0.86Pr0.45。分析表明,在混沌流的作用下,层流状态下的流体可能出现类似湍流的传热效果,初步证实了这种混沌流是强化传热的一种有效的方法。     

Model-based analysis of thermal insulation coatings

Thermal insulation properties of coatings based on selected functional filler materials are investigated. The underlying physics, thermal conductivity of a heterogeneous two-component coating, and porosity and thermal conductivity of hollow spheres (HS) are quantified and a mathematical model for a thermal insulation coating developed. Data from a previous experimental investigation with hollow glass sphere-based epoxy and acrylic coatings were used for model validation. Simulations of thermal conductivities were in good agreement with experimental data. Using the model, a parameter study was also conducted exploring the effects of the following parameters: pigment (hollow spheres) volume concentration (PVC), average sphere size or sphere size distribution, thermal conductivities of binder and sphere wall material, and sphere wall thickness. All the parameters affected the thermal conductivity of an epoxy coating, but simulations revealed that the most important parameters are the PVC, the sphere wall thickness, and the sphere wall material. The model can be used, qualitatively, to get an indication of the effect of important model parameters on the thermal conductivity of an HS-based coating and thereby be used as a specification tool or as a help in the planning of relevant experiments to conduct. Further work with the model must involve additional experiments to secure a general verification of important underlying model assumptions.     

The oscillation of drops and spheres at fluid—liquid interfaces

A theoretical model is presented which successfully predicts the experimental variation with time of the frequency and amplitude of a rigid sphere oscillating at a fluid-liquid interface in terms of radius, height of fall and physical properties, when the sphere is separated from the interface by a draining film. The model may be modified to describe the observed behaviour of liquid drops. In particular it successfully predicts the initial attenuation in amplitude and irregular increase in frequency with time. The amplitude of oscillation increases and frequency decreases with increasing diameter and density of the sphere, and decreasing interfacial tension. Increasing the height of fall (or impact velocity) has a similar, but surprisingly weaker, effect to that of increasing sphere diameter. The model predicts that a 2 mm dia. rain drop should penetrate a water surface by a few millimeters and oscillate with a frequency of about 30 cycles/sec if it does not immediately coalesce.     

环状和支链硬球链流体的状态方程

以单体缔合的统计力学理论为基础，建立了链状分子亥氏孙数和状态方程和空们相关函数的关系，并应用于环 状和支链硬球链流体。对这两类流体压缩因子的预测结果与计算机模型值相吻合。     

Electromagnetically induced chaotic mixing in a pipe mixer

A numerical investigation is carried out to study the mixing by chaotic advection in an electromagnetically driven pipe mixer. It consists of a pipe with two inner electrodes which are energized alternatively. An externally applied magnetic field along the flow direction interacts with the local electric currents inducing a spatially varying electromagnetic body force in the model fluid. The system is an extension of Aref's blinking vortex model to three dimensions. The Lagrangian motion of passive tracer particles is numerically simulated to quantify the degree of stirring. The model predictions indicate that the chaotic mixing is strongly dependent on the modified Hartmann number, the electrode switching frequency and the electrode separation distance. A comparison with numerical simulation results obtained using a dimensional model with glass melt shows that the chaotic mixing behavior of the glass melt is very close to the non-dimensional model predictions. The computational results presented here will be useful for developing efficient glass melt homogenisation systems.     

Bifurcation analysis of two continuous membrane fermentor configurations for producing ethanol

A detailed bifurcation/chaotic investigation of a single continuous fermentor using an experimentally verified model was published earlier by the authors (Chem. Eng. Sci. 58 (2003) 1479); the present paper is an extension of the earlier one. It uses the same biokinetic model to investigate the effects of continuous ethanol removal using permselective membranes, cell recycle with varying cell separation efficiencies and recycle of unused sugars for two configurations of fermentors. The rich static/dynamic bifurcation and chaotic behavior of two different configurations are investigated. The aim is to gain deeper understanding of the complex static/dynamic characteristics of this system as a prelude to a detailed experimental investigation. The emphasis is on achieving higher sugar conversion, ethanol yield and productivity through the exploitation of these characteristics and optimal manipulation of operating and design parameters within the bifurcation/chaotic regions.