Laminar flow in axisymmetric conduits by a rational approach

Numerical and closed-form solutions to laminar flow in regular polygonal conduits, star-shaped conduits, and rectangular conduits are presented. Results by the present approach are shown to be more accurate and the computation to require less effort than conventional methods. The formal finite-series solutions obtained through the present approach lend themselves to parametrization and to a judicious choice of computational schemes. In addition both analytical and numerical procedures yield exact solutions to flow in an equilateral and in an elliptic conduit. The present approach proves to be advantageous in its accuracy, generality, and simplicity.     

Slip Flow in Ducts

Slip flow in ducts occurs in many practical fluid transport situations. The method of eigenfunction expansion and collocation is used to solve the velocity distribution for slip flow in ducts of polygonal, elliptic and cuspidal cross sections. The friction factor‐ Reynolds number products are tabulated.     

Laminar flow in regular polygonal shaped ducts with circular centered cores

The method of least-squares fitting of harmonic functions to known boundary conditions has been employed to obtain closed-form solutions for laminar flow of an incompressible fluid through the constant area annulus between a regular polygonal duct and a centered circular core. The product of Fanning friction factor and Reynolds number has been determined for the entire range between the extreme case of no core and the other extreme case where the core touches the outerwalls. For the latter case, it is shown that when the number of sides of the polygon approaches infinity, f.Re approaches a minimum value of 6.22. The analysis of this case is further extended to corner angles less than 60°, the minimum imposed by an equilateral triangular duct.     

Geometric parameters for some flow channels

A method was proposed earlier⁽¹⁾ for prediction of the average velocity or pressure drop in the flow of non- Newtonian fluids in conduits of arbitrary cross section. The method requires only a knowledge of two geometric parameters which characterize the flow geometry, and the fluid model equation. In this paper, evaluations of geometric parameters are presented for infinite and finite (enclosed)square and triangular arrays of cylinders, and for regular polygonal and star-shaped conduits. With these parameters, predictions of the average velocity or related variables for the Zlow of any arbitrary non-Newtonian fluid can now be made. Comparisons are made with recent analytical solutions and experimental data pertaining to non-Newtonian flow in concentric annuli, and equilateral and right isosceles triangular ducts, which give additional support to the reliability of the proposed method.     

Non-newtonian flow modeling in the mixing section of a single-screw extruder with flow analysis network method

The flow of non-Newtonian fluids obeying the power-law relation through the mixing sections of a single-screw extruder is analyzed with a modified flow analysis network (FAN) method. Three types of mixing elements, the Maddock, the dulmage, and the blister ring elements, are studied. The Maddock and the blister ring elements are dispersive type elements. They generate high pressure drop, and yield a negative pressure gradient which indicates poor pumping capability. The flow fields are rather regular in these elements. On the other hand, the dulmage element is a distributive type element. It generates a low pressure drop, and yields a positive pressure gradient at low extrusion rate which indicates better pumping capability than the dispersive type elements. Extensive flow splitting and reorientation is observed in this element. The power-law exponent has significant effect on pumping characteristics. However, the overall flow patterns of Newtonian fluids and power-law fluids in these mixing elements are quite similar.     

Synthesis of carbon nanofibers with a polygonal cross section by the catalytic decomposition of C2H2 over bi-metal catalysts

Carbon nanofibers with a polygonal cross section were synthesized using catalytic chemical vapor deposition over Fe–Sn, Ni–Sn or Co–Sn catalysts. Their morphologies were characterized by scanning and transmission electron microscopy. Edges connecting of two walls can be clearly observed and some adjacent walls have a V-shape. The lengths of the sides of the polygonal cross sections range from 150 to 500 nm over Fe–Sn or Co–Sn nanoparticles, increasing to 700–900 nm over Ni–Sn nanoparticles. Polygonal catalyst particles can be seen at the ends of the fibers.     

Analysis of the electro-viscous effects on pressure-driven liquid flow in a two-section heterogeneous microchannel

In this paper, the electro-viscous effects on pressure-driven liquid flow through a microchannel which is composed of two heterogeneous sections are analyzed. The Poisson-Boltzmann equation, Navier-Stokes equations and a set of constrained equations are solved analytically to obtain the velocity profiles and the streaming potentials in each section. Effects of the zeta potential and length ratio of the two sections on the flow resistance are discussed by means of the apparent viscosity ratio and the Poiseuille number.     

Characterization of unsteady flow in a 3D-printed Schwarz Diamond monolith using magnetic resonance velocimetry

Process engineering applications such as heat transfer, reactions, and separations involve passing fluid through a porous medium. Historically, random-channel porous media have been used for these operations. Such systems do not represent optimal configurations for process performance because of poor flow distribution and high-pressure drop. It is now possible to fabricate porous monoliths with tailored morphology and regular channel structure using 3D-printing. In this work, we use magnetic resonance imaging to study flow through a Schwarz Diamond triply periodic minimal surface (TPMS) monolith for Reynolds numbers up to 350. A transition to unsteady flow was observed experimentally for the first time. The channel structure diverts flow such that free shear layers form in the channel centers that contribute to flow instability. These measurements serve to inform the design of novel transport processes with enhanced performance.     

Forced in-plane flow through complex deformable structures: Influence of an imposed curve

Forced in-plane flow of liquids through contiguous flat and curved regions of confined fabrics has been studied both as a general phenomenon and for predicting the flow of polymers during injection molding of monolithic composite structures with complex configurations. A controlled pressure difference is applied to drive the flow, while the mass flow rate is measured gravimetrically by Liquid/Air Displacement Analysis (LADA). Measurements have been carried out along fabric paths that are first vertical, then curved, and finally horizontal. Fluid flow equations have been adapted for analyzing flow in the flat sections, leading to the evaluation of permeability constants and capillary pressures. A saturated flow rate measured at constant hydrodynamic pressure is used to evaluate the overall permeability coefficient of the encapsulated fabric. Data are presented showing that permeability can be reduced as a consequence of flow through the curved region.     

同向双螺杆不同螺纹元件混炼效果的数值研究

采用Polyflow软件数值模拟了啮合同向双螺杆挤出机流道内聚丙烯(PP)熔体的流动,数值计算了常规螺纹元件和开槽螺纹元件流道内PP熔体的三维等温流场,采用粒子示踪分析法(PTA)分析了不同螺纹元件流道内粒子的拉伸度自然对数、分离尺度和停留时间,比较了常规螺纹元件和开槽螺纹元件的混炼效果。研究表明,与常规螺纹元件相比,由于熔体在沟槽内产生漏流,开槽螺纹元件的建压输送能力较低,分散混合性能较弱;开槽螺纹元件流道内因粒子的停留时间较长,其分布混合性能优于常规螺纹元件。     

Synthesis and characterization of high-purity aluminum nitride nanopowder by RF induction thermal plasma

High-purity aluminum nitride nanopowder was synthesized using the RF induction thermal plasma technique. The nitrogen gas flow rate, plasma power and reactor pressure were controlled to increase the conversion rate of Al powder to AlN nanoparticles. The compositions of the obtained powders were investigated through XRD and EDS analysis. The synthesized aluminum nitride nanoparticles included polygonal and rod-shaped nanoparticles and ultra-fine particles below 10 nm. The particle sizes generally ranged from 20–60 nm in TEM analysis. The specific surface area, band structure and impurities of aluminum nitride nanoparticles were also evaluated by BET, FTIR and ICP-OES analysis.     

Determination of polymeric medium flow rate in extruders based on a new correlation

One of the most widespread practical methods of polymer processing is the extrusion method that is based on pressing a polymeric melt through channels of the molding tool which have different geometrical cross‐sections. The basic performance of extrusion is based on the pressure and flow performance which sets functional correlation between volumetric flow rate of a polymer medium, pressed through a molding tool, and created pressure drop. Arguments of this correlation are the rheological parameters of polymer and the geometrical characteristics of the channel in which the polymeric melt flows. In this article, a viscoelastic model with a corrected strain energy function is implemented. The comparison of revealed theoretical expression in this article with the experimental data for flow of polymeric melts in cylindrical channels with various cross‐sections demonstrates a good convergence over a wide range of pressure gradient. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers     

Pulsed fluidization—a DEM study of a fascinating phenomenon

An investigation of pulsed fluidization by discrete element method simulation is presented. The particles used were 0.5 mm in diameter and 2650 kg/m³ in density. The pulsed gas flow consisted of a fluctuating component superimposed on a constant component. The effect of gas pulsation was assessed through examination of bed pressure drop and bubble patterns for a wide range of conditions. The influence on fluidized bed behaviour of frequency and amplitude of pulsation, superficial gas velocity of the base flow, and the nature (type) of pulsation was studied. Transition from chaos to ordered behaviour and formation of regular bubble patterns were reproduced. It was found that regular bubble patterns arise from periodical formation of horizontally aligned voids near the distributor plate.     

Polygonal deformation of a metallic foil subjected to impact by an axisymmetric indenter

When a stack consisting of layers of soft elastomer and thin metallic film is subjected to low intensity impact by releasing an axisymmetric spherical indenter from a vertical height, the foils buried within the stack undergoes large deformation and fracture. The shape of the deformed area nevertheless remains circular, its radius first increases with the depth from the surface of the stack and then decreases. In contrast, here we show that the symmetry of the deformed area breaks down when instead of a smooth elastomeric layer, one with topographical patterns is used in the stack. The metallic foil deforms through a polygonal area. The size and shape of the polygonal area vary with the flexibility of foil, geometry and dimension of the patterns and the intensity of the impact. For example, for one elastomeric layer decorated with pillars arranged in a square array, the damaged area turns rectangular to hexagonal and then to octagonal with increasing severity of impact, very much similar to polygonal wetting and spreading by a liquid on a patterned substrate.     

Hydrodynamics of Taylor flow in noncircular capillaries

In this work, volume of fluid (VOF) technique, one computational fluid dynamics (CFD) method, was used to investigate the upward Taylor flow in vertical square and equi-triangular capillaries. For saving computation time, the simulations were carried out in a moving frame of reference attached to Taylor bubbles. The main flow parameters, involving bubble size and shape, liquid film thickness, velocity field and two-phase relative velocity, were studied as functions of capillary number. The numerical simulations were in good agreement with previous reports and showed that the flow in the sides and corners of polygonal capillaries were different. A comparative study was also conducted on Taylor flow in square and equi-triangular capillaries and their circular counterparts, where the influence of capillary geometry on the characteristics of Taylor flow was illustrated clearly.     

多孔介质电渗流动计算流体力学模拟与实验研究（Ⅰ）多孔介质电渗流动的CFD模拟

采用周期性空间模型描述多孔介质,根据电动力学理论及计算流体动力学方法对多孔介质内的电渗流动行为进行数值模拟,得到多孔介质孔内与颗粒表面可视化的流场,并对比了多孔介质中压力场驱动与电场驱动的流体流动特性,显示出电渗在强化固体表面流体流动所具有的优势.     

The permeability of fibrous porous media

The literature was searched for experiments and theories related to low-Reynolds-number flow through fibrous porous media, particularly highly porous structures. Experimental data were found for a wide range of materials, from polymer chains to fiberglass, and the results collapse reasonably well when the appropriate dimensionless co-ordinates are employed. Of the theories, accurate solutions of Stokes equation are available for regular arrays of parallel rods, either aligned with or normal to the flow. For irregular arrays and three-dimensional media, approximate permeabilities can be calculated from several flow models.     

旋流板上流场的LDA实验研究

在φ３００ｍｍ塔内，实现了用二维激光多普勒测速仪对旋流板上气体速度场的测定，获得了不同高度剖面的切向、轴向及径向速度分布的数据，探明了板上气流场的基本特点；还采用气－固流模拟湿板操作，测定了模拟液滴的流场。实验结果证实了旋流板的传统设计思想。     

The Damage Mechanism Route to Better Armor Materials

This paper describes the mechanisms by which brittle materials are penetrated by impacting projectiles, links ballistic performance to fracture behavior, and in turn to microstructure, and suggests a route unexplored previously for achieving better armor materials. Fracture patterns on cross sections through partially penetrated glass and ceramic targets show that deep penetration proceeds by the crushing and subsequent flow of fragments away from the projectile path. Preliminary finite element simulations indicate the likely positive effect of increasing frictional flow resistance of fragments. Tests are envisioned for measuring crush and fragment flow behavior, showing the effects of microstructural variables, guiding mathematical models, and hence leading to a capability to design computationally improved armor materials and structures.     

Experimental investigation and stability analysis on dense-phase pneumatic conveying of coal and biomass at high pressure

Conveying characteristics and flow stability are very important for design and control of a conveying system at high pressure. The influences of operating parameters and material properties on conveying characteristics were investigated in an experimental test facility with a conveying pressure up to 4MPa. Wavelet transform and Shannon entropy analysis were applied to analyzing pressure drops through horizontal pipe in order to obtain the stability criterion. Results indicated that the mass flow rate of biomass decreased, while the mass flow rate of pulverized coal increased at first and then decreased with the increase in fluidization velocity. Solid loading ratios for four kinds of powders decreased with the increase in fluidization velocity. Conveying phase diagrams and pressure drops through different test sections of pulverized coal and biomass at high pressure were obtained and analyzed. The influences of coal category, fracture characteristics and particle size on conveying characteristics were determined.