Wall Effects in Two‐Dimensional Axisymmetric Flow Over a Circular Disk Oriented Normal to Flow in a Cylindrical Tube

The effect of cylindrical walls on the drag of a neutrally buoyant disk (with zero inertia) oriented normal to the direction of flow has been investigated numerically. Using FLUENT, the field equations have been solved to obtain the values of the total, pressure and friction components of drag as a function of the Reynolds number and of the blockage ratio. The results presented herein encompass the following ranges of the conditions: Reynolds number: 1 to 100; and the blockage ratio (disk diameter/cylinder diameter): 0.02 to 0.5. As expected, the drag is found to be higher under the confined flow conditions than that in the unconfined flow conditions. However, the confining boundaries appear to exert only a weak influence on the formation and size of the wake region. The drag values are also weakly influenced by the thickness of the disk. However, this effect progressively disappears as the Reynolds number is gradually increased. The present numerical values corresponding to the unconfined flow conditions are in excellent agreement with the previous numerical and experimental results available in the literature.     

低粘附功管壁的内流减阻研究

以乙烯基三乙氧基硅烷 无水乙醚溶液处理玻璃管道内壁 ,降低流体水与管壁间的粘附功 ,研究了低粘附功内壁管道的内流减阻性能。结果表明 ,在管壁与液体间的粘附功小于液体的内聚功条件下 ,当雷诺数大于临界雷诺数时 ,低粘附功内壁管道呈现明显的内流减阻效果 ,临界雷诺数的值与一定的临界壁面剪力值或层流底层临界厚度值相对应 ;在减阻区内 ,减阻率随雷诺数的增加及管道内径的减小而增大 ,阻力系数的无因次关联式可表示为λ=f (Re ,X) ,其中X为无因次数群 [W / (du2 ρ) ]。     

中等质量分数CTAC表面活性剂溶液减阻性能实验研究

表面活性剂减阻由于其机械、化学、光、热稳定性 ,越来越为工程界所重视。文中开展了目前较少研究的中等质量分数 (采用 170、 80 0 μg g两种质量分数的溶液 )CTAC (Cetyltrimethylammoniumchloride,十六烷基三甲基氯化铵 )溶液与伴随离子 (Sal+ )共存条件下的减阻实验。研究表明 ,在一定CTAC及伴随离子质量分数范围内 ,溶液的减阻性能随CTAC及伴随离子质量分数的增加而下降 ;伴随离子在高雷诺数区域对减阻效应几乎没有影响 ;溶液的减阻性能曲线没有明显的“发生 (onset)”点。对以上实验观测到的现象机理进行了探讨     

Relationship between droplet size and fluid flow characteristics in miniemulsion polymerization of methyl methacrylate

Static mixer (SM) can be applied for emulsification, but the fundamental understanding of the nature of fluid flow and mixing in static mixers, is however poor. Droplet size is a very important parameter in miniemulsion systems and affects strongly the mechanism of particle formation in polymerization reactions. In this study, static mixer was used as homogenization device for emulsification of methyl methacrylate (MMA). Re number (Re) was obtained for SM inserted tube in different flow rates. It was demonstrated the nature of fluid flow was turbulent under our experimental conditions. The relationship between droplet size—the most important variable in our study—and Weber number (We) was investigated. The results showed that the ratio of the droplet size to the pipe diameter was fit as an exponential function with an order of −0.35. The polymerization of created droplets under certain We values by SM showed that it is possible to obtain a reasonable 1 : 1 copy of droplets to the particles. All these, indicate that using relationship between We and droplet size allow one to obtain acceptable condition of droplet nucleation in miniemulsion polymerization. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

粘性SiC颗粒聚团流态化特性

对不同粒径的°SiC粘性颗粒的流态化实验表明,颗粒粒径对流化性能有较大影响,颗粒粒径越小,颗粒间粘附力越大,其流化性能越差;提出了粘性颗粒自然聚团数Ae_n和流态化聚团数Ae_f,用来表征颗粒的流化性能;指出了应开展粘性颗粒聚团流态化的研究。     

基于动态平衡预测纳米颗粒流化床内聚团尺寸分布

准确预测纳米颗粒流化床内聚团尺寸对研究纳米颗粒流化具有重要意义。鉴于目前文献中主要根据力平衡模型得出聚团尺寸平均值,然而聚团尺寸实际呈宽筛分分布,本工作从动态平衡角度,采用分子动理论中麦克斯韦气体速率分布律类比流化床内聚团速度分布,建立基于微观作用力的聚团解聚—重聚模型,并用以预测纳米颗粒流化床内聚团尺寸分布。通过比较聚团间结合力和分离力的相对大小,判断聚团结合和破碎;在分离力中,碰撞力起着至关重要的作用,且与聚团相对运动速度关系密切。预测结果显示,纳米颗粒流化床内聚团尺寸呈现卡方分布。将模型预测值和文献中的实验数据进行对比,包括TiO_2、Ni、SiO_2等颗粒的团聚尺寸,发现大部分偏差在20%以内。     

Terminal settling velocity and drag coefficient of biofilm‐coated particles at high Reynolds numbers

The drag force (F_d) on bio‐coated particles taken from two laboratory‐scale liquid–solid circulating fluidized bed bioreactors (LSCFBBR) was studied. The terminal velocities (u_t) and Reynolds numbers (Re_t) of particles observed were higher than reported in the literature. Literature equations for determining u_t were found inadequate to predict drag coefficient (C_d) in Re_t > 130. A new equation for determining F_d as an explicit function of terminal settling velocity was generated based on Archimedes numbers (Ar) of the biofilm‐coated particle. The proposed equation adequately predicted the terminal settling velocity of other literature data at lower Re_t of less than 130, with an accuracy >85%. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Homogeneous drag models in gas–solid fluidization: Big data analytics and conventional correlation

The drag force model is vital for capturing gas–solid flow dynamics in many simulation approaches. Most of the homogeneous drag models in the literature are expressed as a function of phase fraction (ε) and particle Reynolds number (Re_s). In this work, we use a “big data” approach to analyze ~10⁸ data points for drag coefficient (F_d) for Geldart Group A particles at atmospheric pressure and find that the contribution of Re_s on F_d is much less than ε based on the Maximal information coefficient analysis. Thus, these drag models are separately reduced to machine learning and conventional expressions only related to ε. The reduced models achieve almost the same predictive performance as the originals in bubbling, turbulent, and jet fluidizations. Moreover, the reduced models provide better numerical stability for coarse grid simulations. These findings provide new insights into the drag coefficient for Geldart Group A particles under full fluidization conditions.     

密相流化床中介尺度流动结构的流体力学特性研究

在一套流化床冷模实验装置中对黄沙颗粒和黄沙-硅微粉 （20 μm）混合颗粒进行实验。测量固含率时间序列信号并进行统计分析,提出并建立复杂光纤脉动信号的解耦方法,实现稠密气固流中介尺度流动结构的准确识别。基于统计矩一致性原理提出气泡阈值的计算方法,通过遍历法确定气泡阈值。对气泡阈值变化规律进行分析,发现加入细颗粒有助于改善流化质量,随表观气速的增加,气泡阈值减小。对气泡、乳化和聚团三相的相分率进行统计,发现在黄沙颗粒中加入少量（5%,质量分数）细颗粒能够显著改善流化质量,细颗粒添加量过多时（10%）,对流化质量的改善将减弱。对气泡的流体力学特性进行分析,发现加入10%硅微粉后,气泡弦长增大,频率降低,速度略有降低。对颗粒聚团流体力学特性进行分析,发现随硅微粉含量增加,表观气速对聚团速度的影响减弱,聚团弦长略有减小。加入5%硅微粉后,颗粒聚团的出现频率较小且径向上分布均一。加入10%硅微粉后,聚团频率有所增大,说明加入过多硅微粉会促进聚团的形成。     

Effect of Blockage on Heat Transfer Phenomena of Spheroid Particles at Moderate Reynolds and Prandtl Numbers

Effects of the confining wall or blockage on the heat transfer phenomena of spheroid particles were numerically investigated. The heated spheroid particles were maintained at constant temperature and allowed to sediment in cylindrical tubes filled with Newtonian liquids. In this flow configuration, the heat transfer took place from the heated spheroid particles to the surrounding Newtonian liquid. The governing conservation equations of the mass, momentum, and energy together with appropriate boundary conditions were numerically solved using commercial software based on computational fluid dynamics. A simple correlation for the average Nusselt number of the confined spheroid particles was developed which can be applied in new applications.     

Research of mass-transfer in fibrous sorption-active materials

The mass-transfer processes in fiberglass were studied in the course of drying the saturated glass fabric sample. Experiments were carried out using an Avance DRX Bruker spectrometer equipped with a micro tomography device. Experimental signal intensities of fluids flowing at different velocities were obtained. A one-dimensional mathematical model was applied to calculate mass-transfer coefficients from experimental data. Dependencies Nu(Re) at the Reynolds number varied between 0 and 400 were obtained at different fluid velocities. The data obtained were compared to correlation dependencies for woven Pt/Pd gauzes and for rows of parallel cylinders. Numeric experiments of gas flow filtration at low Reynolds numbers (Re < 1) were carried out using the CFD FLUENT software package. Fibrous material was represented as porous system consisting of bunches of parallel cylinders with varied distances between the cylinders. Dependence Nu(Re) was calculated at various parameters of system.     

Turbulent dispersion coefficients in cyclone flow: An empirical approach

Among the various theories available to predict cyclone collection efficiency, the finite diffusivity theory of Mothes and Loffler (1988) has been shown to give the best fit of the observed grade-efficiency curves. However, lack of knowledge on the dependence of the particles' turbulent dispersion coefficient with cyclone geometry, operating conditions and particle size has so far hindered the application of this theory for predictive purposes and for improved cyclone design. In this work, this theory is applied for predictive purposes, through the use of an empirical relation for the particles turbulent dispersion coefficient. The proposed relation is based on an analogy with turbulent dispersion in packed beds, and correlates the particle radial Peclet and Reynolds numbers. Laboratory-scale reverse-flow cyclones of previously unpublished geometries were built to test the applicability of the proposed relation. The Mothes and Loffler (1988) theory, when coupled with the proposed estimates of turbulent dispersion coefficients, is a powerful tool for predicting cyclone collection efficiency, short of using computational fluid dynamics tools.     

Artificial neural network based modelling of head and power characteristics of pump-mixer

Present work involves detailed experimentation on pump-mixer, and processing of experimental data to model its head and power characteristics using multi-variable least square based empirical correlations and artificial neural network (ANN). The latter modelling technique is shown to be superior. Trained and frozen ANN model has been used to generate head and power characteristics. Wherever possible, these characteristics have been qualitatively compared with the observations reported earlier. Also, an attempt has been made to physically explain these characteristics in order to demonstrate that the ANN model successfully captures the physics of the system.     

中等Reynolds数线性剪切泡状流的液相雷诺应力

Analytical investigation of liquid Reynolds stress in shear bubbly flow with intermediate Reynolds numbers is absent. In this paper, the velocity field around a sphere bubble in linear shear liquid is assumed to be the linear superposition of the velocity field of uniform liquid passing a sphere bubble and the linear shear velocity field. The formula of shear liquid Reynolds stress was derived by averaging the velocity field in the cell-ensemble averaging method, and the formula was corrected under conditions of intermediate Reynolds number. The formula was compared with that of Sato, and the predicted results of local liquid velocity of the fully developed upward bubbly flow in pipes were compared with the experimental data. The results show that the formula is valid and accurate in prediction.     

Local mass transfer measurements from a submerged jet parallel to a flat surface

The local mass transfer rates from a submerged vertical jet parallel to the vertical electrode surface were measured by a limiting current density technique. For these studies, the parameters considered are a plate Reynolds number in the range of 1965 to 136500, electrode height over the orifice of the jet (Y) which varied from 0 to 12 times the jet orifice diameter (d), and the vertical distance of the microelectrode on the electrode plate in the range of 0.7 to 12.5 cm. The system used for measuring the limiting current was the reduction of copper ions. The relationship between the local Sherwood number (Sh) and Reynolds number (Re) was found to be Sh = 0.0004(Re)^1.5 (Sc)^0.33 This relationship is valid for Y/d ≤ 6.0.     

高雷诺数下变截面分流歧管面积比对流体分配性能的影响

在高雷诺数(Re=5×105～30×105)下,对不同主管形状和面积比的分流歧管流体分配性能进行数值模拟.通过计算各支管出流流量比(Q/Qave)与流量分配均匀性指数(U),分析Re和主管形状以及面积比(AR)对分流歧管流量分配性能的影响.结果表明,与低Re下的分流歧管流量分配性能高度依赖于Re的规律不同,高Re(5×...     

储层流体流态判定方法研究

以低渗透油田的开发实践为背景,应用雷诺数法和压力数法综合判断地层流体渗流特征,指出了判定达西流非达西流的临界雷诺数和临界压力数,从而判断出地层流体渗流特征。     

超声空化对换热器场协同影响研究

针对超声波在防除垢对换热器场协同的影响,采用FLUENT软件中的两相流模型、空化模型和标准k-ε的湍流模型,获得流场压强随时间步长的变化规律——流场波动呈类似正弦波波动.引入空化数的概念;利用π定理推导雷诺数和空化数的函数关系——雷诺数与空化数呈幂函数关系,雷诺数随着空化数的增加而减小;根据场协同原理,表示出空化数和场...