Pressure Drop Studies on Flow of Viscoelastic Fluid Through a Packed Bed

In the present study, pressure drop-flow rate behavior for the flow of viscoelastic fluid through porous media has been investigated. Aqueous solutions of polyacrylamide (PAM) and water in the concentration range of 0.02 to 0.1% wt/vol were used to elucidate the effect of fluid elasticity on bed pressure drop. Based on the observed data, the existing pore model was extended to predict the bed pressure drop for viscoelastic fluid flowing through a porous media. A statistical comparison between the existing models and the present model was made. The proposed correlation based on modified pore model predicts the data well to within a reasonable accuracy of ±10% with arithmetic relative error (%ARE) and mean relative quadratic error (MRQE) of 8.3% and 0.122, respectively.     

Creeping Flow of Viscoelastic Fluid Through a Packed Bed: Effect of Particle Shape and Porosity

Experiments were conducted to elucidate the effect of particle shape and porosity on frictional pressure drop for the flow of viscoelastic fluids through a packed bed under creeping flow regime. Extensive pressure drop-flow rate data were generated using different packing materials such as cylinders of different aspect ratios, square plates, triangles, and spheres covering a wide range of sphericity, 0.546 ≤ φ ≤ 1. Effect of bed porosity has been determined using uniform-size spheres of different diameters (4.38 mm, 5.76 mm, and 6.78 mm), covering column to particle diameter ratio in the range of 13.96–21.62; while porosity varies in the range of 0.345–0.375. The experimental results indicate that the modified Ergun correlation, proposed by Sobti and Wanchoo (2014 Sobti, A., and R. K. Wanchoo. 2014. Creeping flow of viscoelastic fluid through a packed bed. Industrial & Engineering Chemistry Research 53:14508–14518.[Crossref], [Web of Science ®] , [Google Scholar]), can adequately be applied for the nonspherical particles, provided the equivalent volume mean diameter (D_eq) together with sphericity (φ) is used instead of the diameter of the spherical particle (D_p), i.e., D_p = D_eqφ. Further, an attempt has been made to suitably define a packing structure parameter, [(1 ? ?)/(? φ)], which could well capture the balancing effect between porosity and sphericity.     

On the Modeling of Flow in Packed Bed Systems

Modeling of flow and its impact on transport phenomena in packed bed systems is discussed. A detailed flow model based on an improved Brinkman equation has been derived and its solution is presented. This model incorporates a representative voidage function that enabled the generation of velocity profiles that closely followed the voidage profile and highlighted the importance of the wall zone. Two approximate flow models from the literature have been used to obtain velocity profiles for the purpose of comparison with the model derived herein. Significant differences were observed in the location and magnitude of velocity maxima predicted by the various models employed in this work. The impact of such findings on transport phenomena is discussed. A method to obtain a wall zone velocity is suggested to facilitate estimation of transport parameters near the wall.     

On the Modeling of Flow in Packed Bed Systems

Modeling of flow and its impact on transport phenomena in packed bed systems is discussed. A detailed flow model based on an improved Brinkman equation has been derived and its solution is presented. This model incorporates a representative voidage function that enabled the generation of velocity profiles that closely followed the voidage profile and highlighted the importance of the wall zone. Two approximate flow models from the literature have been used to obtain velocity profiles for the purpose of comparison with the model derived herein. Significant differences were observed in the location and magnitude of velocity maxima predicted by the various models employed in this work. The impact of such findings on transport phenomena is discussed. A method to obtain a wall zone velocity is suggested to facilitate estimation of transport parameters near the wall.     

超重力反应结晶法制备纳米硫化锌实验研究

本文以硝酸锌和硫化氢气体为原料,用超重力反应结晶法制备纳米硫化锌粒子。探讨了陈化时间、反应物浓度、反应温度、旋转床转速等工艺参数对产品粒径与转化率的影响规律,确定了最佳工艺条件为：陈化时间48h,反应物浓度0．1mol/L,反应温度45℃,旋转床转速1500-1800r／min。TEM分析表明,所制备的硫化锌干粉平均粒径为42nm,分散性好,颗粒之间没有明显的团聚现象。     

工业反应炉中气体流动压力的数值模型

本文构造了工业反应炉中气体流动压力的离散化方程，同时证明了方程解的存在性和唯一性。     

旋转填充床中反溶剂重结晶法制备超细硫酸沙丁胺醇实验研究

本文在旋转填充床中用反溶剂重结晶方法对硫酸沙丁胺醇原料药品进行了细化.研究了结晶温度、反溶剂与硫酸沙丁胺醇水溶液流量比、旋转填充床转速等操作参数对硫酸沙丁胺醇颗粒大小及收率的影响.实验结果表明,采用较低的结晶温度、较大流量比和较大旋转填充床转速可以得到粒度小于500nm的硫酸沙丁胺醇颗粒.     

颗粒流的离散元法模拟及其进展

颗粒流问题是众多工农业生产领域中的常见问题,然而人们至今对颗粒流机理认识不深。目前一种基于离散元的数值模拟方法被用以模拟和分析颗粒流问题,研究实践表明该方法是散体力学分析的一种有效的工具。本文介绍了颗粒流研究的背景以及离散元法的发展过程,概述了颗粒流动力学研究的动理论模型和摩擦塑性模型,综述了离散元法的理论和各种颗粒作用模型及其在粉体工程领域的应用,讨论了颗粒流研究的主要困难和离散元法发展中亟待解决的问题。     

粘结颗粒材料双轴试验的数值模拟研究

利用离散元法数值模拟了5组试件的双轴试验,得到了粒径对弹性模量、泊松比、强度和裂缝初始应力的影响,分析了20MPa围压条件下粒径与弹性模量、泊松比、强度和裂缝初始应力的关系,以及6种围压与裂缝初始应力的关系,给出了5组试件荷载作用后颗粒间的接触力和颗粒位移矢量,从细观角度阐释了荷载作用下颗粒的运动模式。模拟结果表明,随着粒径的增大,弹性模量、强度和裂缝初始应力均呈减小的趋势;随着围压的增大,各粒径范围试件的裂缝初始应力呈增加的趋势,并且粒径越大的试件最大接触力和最大位移越大。     

Pressure Drop and Gas Holdup Studies in a Spout-Fluid Bed

Spout-fluid beds are used for a variety of processes involving particulate solids. They are employed where the particle agglomeration, dead zones, and sticking of particles to the vessel are the common problems in conventional spouted beds. Applications involved are granulation, coating, drying, combustion, and gasification. In this study, experimental studies have been carried out in a cylindrical Perspex column (0.094 m internal diameter and 1.217 m height) using glass beads and air. The effects of initial bed loading, spout velocity, and background (fluidization) velocity on pressure drop and gas holdup have been investigated. It is found that the minimum spout-fluidizing velocity increases with increase in initial bed loading. The pressure drop and gas holdup increase with increasing bed loading. In spout-fluid bed condition, at a constant spout velocity, as the background gas velocity increases, the gas holdup increases, and it is found to be high for smaller bed loading and is low for larger bed loading at higher velocities. The fountain height increases as spouting velocity increases and it decreases with initial bed loading. The total velocity required to fluidize the particles in spout fluidization is lower in comparison to spouted beds and fluidized beds.     

Numerical Investigation of Crater Phenomena in a Particle Stream Impact onto a Granular Bed

This paper presents an experimental and numerical study of the impact of a particle stream onto a particle bed using a 2D slot model. The numerical simulation is performed by means of the discrete element method (DEM). The results show that the DEM simulation can reproduce the experimental results well under comparative conditions. The dynamics in the formation of a crater is then analyzed in terms of velocity field, force structure, bottom stress distribution and energy exchange based on the DEM results. It is shown that as a result of impact by the falling particles, the particles in the top central region of the particle bed have relatively large velocities and contact forces. The velocities and forces propagate into the bed, and reach the bottom of the base layer quickly. They then continue to propagate leftwards and rightwards to create a crater. During the impact process, most of the energy from the falling particles is dissipated due to the inelastic collision and frictional contacts between particles, and only a small amount of the energy contributes to the formation of the crater. The crater size is shown to be affected by the discharging rate, discharging height and materials properties, and be related to the ratio of the input energy from the falling stream to the inertial energy from the original packing.     

An Experimental and Numerical Study of Transversal Dispersion of Granular Material on a Vibrating Conveyor

The mixing of thin granular layers transported on the surface of an oscillating trough is experimentally and numerically examined. The particle dispersion was experimentally quantified by an image processing system recording the growth of the mixing layer thickness of two differently colored but otherwise identical sand particle streams along the longitudinal position within the transporting channel. Granular flow and dispersion on the vibrating conveyor were studied numerically based on a three-dimensional discrete element code. Both experiments and simulations were used to derive quantities characterizing the transversal dispersion. The mixing was found to be directly proportional to the vertical acceleration of the conveyor and inversely proportional to the mass flow of the transported material. Keeping the above-mentioned parameters constant, the dispersion increases with increasing mean particle diameter. When performing the experiments with materials of different mean particle diameters and tuning the mass flow to achieve the same level of dimensionless bed height, the magnitude of the dispersion coefficient remains constant, as was also confirmed by the numerical simulation.     

Slugging Behavior of Geldart D Particles in a Vibrated Gas-Fluidized Bed

The periodic slugging behavior of Geldart D particles in a vibrated gas-fluidized bed (VFB) is favorable for some applications involving the processes of particles stratification, especially for fine coal beneficiation in a VFB. It is of great significance to conduct systematic studies on slug formation, slug coalescence and growth, slug rising velocity, and slugging frequency in a VFB of Geldart D particles. The slug formation model is proposed based on theoretical analysis and indicates that the vibration amplitude, the vibration frequency, and the superficial air velocity all have significant effects on the slugging behavior. Also, the comparison of predicted values and measured values of the slug height at its initial formation verifies that the slug formation model has high prediction accuracy. The dynamic of the coalescence of bubbles into an adjacent slug is qualitatively studied and the correlations of the slug height and the slug rising velocity are established, respectively. The results show that the slug height increases with the excess fluidizing air velocity and the height of slug location, and the slug rising velocity performs an exponential growth with the increase of slug height. The results also show that the slugging frequency is independent on the superficial air velocity.     

FE Analysis of Shearing of Granular Bodies in a Direct Shear Box

A plane strain analysis of a deformation and stress field in cohesionless granular bodies during shearing in a direct shear tester was performed with a finite element method on the basis of a hypoplastic constitutive law enhanced by polar quantities: rotations, curvatures, couple stresses, and a mean grain diameter used as characteristic length. The constitutive law takes into account the effect of pressure, void ratio, direction of deformation rate, mean grain diameter, and grain roughness on the material behavior. The FE calculations were carried out with a different initial void ratio, vertical load, mean grain diameter, and specimen length. Attention was focused on the size effect caused by the size of microstructure related to the specimen dimensions and the effect of side boundaries on the shear zone formation. The FE results show that the thickness of the shear zone increases with increasing initial void ratio, pressure level, mean grain diameter, and specimen length. Due to the effect of boundary conditions, the thickness changes along a horizontal midsection (it is widest in the mid-region).     

Evaluation of styrene-butadiene latex as a vibration damping admixture for concrete: a micromechanical analysis

Abstract

The styrene-butadiene latex as an admixture for Portland cement concrete is evaluated in this study using a numerical simulation approach aided by a series of laboratory experiments conducted for material parameter determination and numerical model validation. Using the discrete element method (DEM), a three-dimensional (3D) beam of concrete was built with due consideration of the concrete microstructural features. The beam was employed to simulate the cyclic three-point flexural test at three loading frequencies: 0.2, 1 and 5 Hz and a representative in-service temperature: 25 °C. The effects of admixture usage and loading frequency on the overall damping properties of concrete were evaluated to explore the vibration-reduction mechanisms of the latex-admixtured concrete. Results show that a 20 percent usage of styrene-butadiene latex (by weight of cement) was found to significantly enhance the storage and loss moduli and the loss tangent of concrete. The developed 3D DEM model realistically accounts for the micro-structural features of concrete matrix and can potentially be used for evaluating and designing high performance concretes against detrimental dynamic loads.     

塑料微管气辅挤出中内气垫层气体的影响

塑料微管尺寸极小,挤出时熔体离开口模时仍为熔融态,内气垫层气体离开口模后仍在微管腔内流动,会对微管成型产生影响。为此,建立了考虑塑料微管腔内气体流动的双气垫层气辅挤出模型,重点分析内气垫层气体离开口模后的流动对微管成型的影响。通过对管壁内外双层气垫层作用下微管挤出成型过程的有限元数值模拟和实验研究,得到了微管型貌、速度、压力降和第一法向应力差等分布。分析表明,当气体离开口模后,由于外气垫层气体离开口模后进入空气中瞬间减压,而内气垫层气体离开口模后进入微管腔内,仍有一定压力,致使微管管壁内侧气压较外侧气压更大,从而导致微管直径逐渐增大;熔体在口模出口处及出口模后,均有第一法向应力差的产生,分析表明,这与微管形貌、壁厚、流速及压力降等的变化存在较大的关联。考虑了微管腔内气体流动的几何模型更符合实验中当气体压力较大时微管壁面出现凹凸波纹现象,口模出口处微管管壁迅速变薄及口模外部微管管壁逐渐变薄的现象。     

空气中环戊烷气体标准物质的研制

称量法制备空气中环戊烷气体标准物质,采用气相色谱法进行均匀性、稳定性考察及比对分析,确保数值准确可靠。空气中环戊烷的浓度范围为（0．1—1．0）×10^-2（mol／mol）。     

循环流化床底部区域流动特性的数值模拟

基于欧拉两相流模型计算循环流化床底部区域的流动特性。在低气速(1.0～2.5m/s)、低循环量下(5.2～34.5kg/(m2·s)),模拟时黏性采用层流模型取得了较好的效果。实验采用光导纤维探头测量仪测量流化床底部区域3个截面的局部颗粒浓度,模拟计算了循环流化床底部3个截面的颗粒浓度的径向分布,并同循环流化床装置的实验数据进行了对比。结果表明,数值模拟计算与实验结果相吻合。     

Efficient Simulation of Gas Flow in Blast Furnace

Simulation of gas flow in a multilayered non-isothermal packed bed is useful for blast furnace operators in deciding appropriate charging strategy. While using an anisotropic form of Ergun equation to simulate gas flow through such systems, a new solution methodology for non-isothermal gas with varying density flowing through a layered burden has been proposed. This involves handling non-linearity due to gas density variation with pressure and temperature by solving for the square of pressure instead of pressure directly and handling the non-linearity due to |v| term in the Ergun equation by solving linearized form of Ergun equation and updating |v| iteratively. The proposed scheme is capable of predicting the effect of layer structure on gas flow with economy in number of grid points as well as computation time.     

粒径分布对循环床内颗粒速度分布的影响

利用激光相位多普勒粒子分析仪（PDPA），在截面尺寸为100mm×15mm的二维循环流化床实验装置上测量比较了平均粒径基本相同的3种不同粒径分布的玻璃珠颗粒在相同操作气速下的颗粒时均速度、脉动速度与数量密度的截面分布特性；初步考察了粒径分布对气固并流上行两相湍流流动行为的影响问题。