Modeling and Experimental Validation of Rheological Transition During Foam Flow in Porous Media

Transport in Porous Media - Flow of nitrogen foam stabilized by alpha olefin sulfonate (C14-16 AOS) was studied in a natural sandstone porous media using X-ray Computed Tomography. Foam was...     

Effect of Confining Wall on Properties of Gas Flow Through Metal Foam: An Experimental Study

While the Darcy and Forchheimer relations are widely applied to determine the permeability and the form drag coefficient of open-cell metal foam, they both assume that the porous medium is infinite in all directions, i.e., large enough so that the effect of any confining walls is negligible. Many researchers, however, pay little or no attention to the size of metal foam samples in pressure-drop studies. The size of a foam sample perpendicular to the flow direction may be small enough such that wall effects are significant. This article experimentally investigates the wall effect on the permeability and form drag coefficient for two types of open-cell aluminum foam subjected to airflow entering the foam in the Forchheimer regime. The Forchheimer equation was recast in two different manners, which resulted in new non-dimensional numbers that correlated very well with the diameter of the foam samples measured in cells. The correlations are valid for a confining-tube-diameter-based Reynolds number ranging from approximately 13,000 to 105,000, and for diameters ranging from 12 to 36 cells and 24 to 60 cells for 10- and 20-pore per inch foam, respectively. The obtained correlations allow for determining pressure drop given only the velocity and the diameter of an aluminum foam sample.     

Experimental Study of Open-Cell Cellular Structures with Elastic Filler Material

Open-cell cellular structures have a high potential for use in automotive, railway, ship and aerospace industry as crash energy absorbers. This paper focuses on the influence of the second phase filler material as a way to further increase the capability of cellular material energy absorption. The behaviour of ductile (aluminium alloy) and brittle (polymer) cellular structures with regular topology with and without the pore filler (silicon rubber) under quasi-static and dynamic compressive loading conditions has been experimentally studied and evaluated. The base material properties of the aluminium alloy and the polymer were obtained with separate experimental testing. The use of second phase filler material resulted in significant changes in cellular material behaviour. It was observed that the pore filler material increases the capability of energy absorption and furthermore improves and stabilises the response of a brittle cellular structures. This paper was presented during the Advanced Computational Engineering and Experimenting ACE-X 2007 Conference, Portugal, July 12–13, 2007.     

基于相场模型的金属微波烧结演化机制分析及同步辐射断层扫描实验验证

为了探索不同种类金属材料的微波烧结机制,本文针对钛和铝两种具有不同电磁学特性的金属材料,分析了微波与金属微粒的相互作用。依据经典的麦克斯韦方程,金属表面产生电子涡流和趋肤效应。由P.Mishra和K.I.Rybakov等提出的金属在微波中的加热效率理论,推导出钛金属表面的热效应明显高于铝。因为电子涡流在磁场中产生指向颗粒内部的洛伦兹力这一微波非热效应,阻碍了内部物质向外的扩散,且铝的感应涡流大于钛,故其向心力更大。由于微波的热效应和非热效应导致物质扩散的驱动力不同,得出"钛的微波烧结速率明显大于铝"这一区别于常规烧结的结论。将获得的分析结果引入相场数值模拟,改变相场模型中控制演化过程中的表面和体扩散变量,获得不同的模拟结果,定量分析了烧结颈等微观结构参数随模拟时间的演化曲线。结合同步辐射断层扫描(SR-CT)技术获得的金属在微波烧结过程中的实验参数,与理论分析和模拟结果相吻合,从而验证了分析和模拟的正确性和可行性。上述结果可为研究金属在微波烧结过程中的演化机制提供支持。     

Surfactant Concentration and End Effects on Foam Flow in Porous Media

Foaming injected gas is a useful and promising technique for achieving mobility control in porous media. Typically, such foams are aqueous. In the presence of foam, gas and liquid flow behavior is determined by bubble size or foam texture. The thin-liquid films that separate foam into bubbles must be relatively stable for a foam to be finely textured and thereby be effective as a displacing or blocking agent. Film stability is a strong function of surfactant concentration and type. This work studies foam flow behavior at a variety of surfactant concentrations using experiments and a numerical model. Thus, the foam behavior examined spans from strong to weak.Specifically, a suite of foam displacements over a range of surfactant concentrations in a roughly 7m², one-dimensional sandpack are monitored using X-ray computed tomography (CT). Sequential pressure taps are employed to measure flow resistance. Nitrogen is the gas and an alpha olefin sulfonate (AOS 1416) in brine is the foamer. Surfactant concentrations studied vary from 0.005 to 1wt%. Because foam mobility depends strongly upon its texture, a bubble population balance model is both useful and necessary to describe the experimental results thoroughly and self consistently. Excellent agreement is found between experiment and theory.     

Numerical Simulation and Experimental Validation of the Turbulent Combustion and Perlite Expansion Processes in an Industrial Perlite Expansion Furnace

A computational code has been developed based on a Eulerian–Lagrangian approach in order to model the combustion and the motion of perlite particles in a vertical expansion furnace. The expansion of a single particle, which takes place during its motion in the furnace, has been modeled by taking into account the perlite chemical composition and the gradual variation of the temperature distribution inside the grain. Experiments, performed in a perlite expansion plant, have been used to validate the computational results. The operational characteristics of a perlite expansion furnace have been measured and have served as inlet conditions for the numerical simulation of the combustion and perlite expansion processes.The good agreement between measurements and predictions indicates that the developed computational tool can be used to optimise the perlite expansion process leading to reduced fuel consumption with increased productivity.     

含冲击损伤高强中模碳纤维复合材料层压板压缩剩余强度分析与试验验证

论文以碳纤维复合材料层压板为研究对象,发展了一种模拟复合材料层压板冲击及冲击后压缩的一体化数值分析方法．基于Puck 失效准则和粘聚区模型描述层内损伤与层间损伤,分别采用基于断裂能的双线性型、函数型以及直接折减型等不同损伤折减方法构建了层内损伤预测与演化模型;建立了碳纤维复合材料冲击后压缩数值仿真模型,通过开展不同能量冲击后压缩试验,验证了所发展的数值分析方法的有效性;研究结果表明,采用Puck 失效准则和基于断裂能的双线性损伤演化模型预测冲击后压缩强度时具有较高精度．     

Correlation Between Foam Flow Structure in Porous Media and Surfactant Formulation Properties

Transport in Porous Media - The optimization of foam injection in porous media for enhanced oil recovery or soil remediation requires a large screening of surfactant formulations. Tests of foam...     

Hydrodynamic Characterization of Nickel Metal Foam,Part 1: Single-Phase Permeability

This article presents results of the investigation of the fluid dynamic behavior in CVD processed nickel metal foams. An experimental facility was developed to measure the single-phase permeability in nickel metal foams in Darcian flow regime. Data on permeability values of seven different nickel foam samples was obtained. The pore sizes of the foam were obtained with scanning electron microscope. By defining friction factor and Reynolds number based on the permeability length scale a correlation was obtained for the foam permeability in Darcian flow regime. The result from this study was compared with the correlations reported by other researchers, and was found to be in good agreement.     

Metal Foam Heat Exchangers for Heat Transfer Augmentation from a Cylinder in Cross-Flow

A numerical study has been conducted to examine the heat transfer from a metal foam-wrapped solid cylinder in cross-flow. Effects of the key parameters including the free stream velocity and characteristics of metal foam such as porosity, permeability, and form drag coefficient on heat and fluid flow are examined. Being a determining factor in pressure drop and heat transfer increment, the porous layer thickness is changed systematically to observe that there is an optimum layer thickness beyond which the heat transfer does not improve while the pressure drop continues to increase. This has been verified by the application of Bejan’s Intersection of Asymptotes method. Results have been compared to those of a finned-tube heat exchanger to observe much higher heat transfer rate with reasonable excess pressure drop leading to a higher area goodness factor for metal foam-wrapped cylinder.     

A New Stochastic Bubble Population Model for Foam Flow in Porous Media

Foam has been widely used as a mobility control agent for Improved and Enhanced Oil Recovery IOR/EOR, gas blocking, and acid diversion during matrix stimulation. The prediction of foam performance relies on macroscopic modeling. Traditionally, foam modeling approaches include fractional flow theories and population balance models. However, fractional foam models assume implicitly that foam is incompressible and do not account directly for the evolution of bubble population. The population balance models, instead, rely on the idea that foam mobility depends on bubble density and are more comprehensive. Yet, population balance models did not gain full acceptance thus far, because of their perceived complexity, with parameters that are hard to obtain experimentally. This article presents an improved foam model based on a simpler but realistic foam rheology and stochastic bubble generation ideas. Physical ideas in agreement with pictures emerging from recent foam studies using X-ray computed tomography form the basis for the new model.     

Lonsdaleite Model of Open-Cell Elastic Foams: Theory and Calibration

We formulate a unit-cell model of open-cell elastic foams. In this model, a foam consists of four-bar tetrahedra arranged in the hexagonal diamond structure known as Lonsdaleite. The parameters of the model are the Young??s modulus of the bars and a few geometric parameters, the values of which may be roughly estimated for any given foam. We use the model to simulate a set of experiments in which elastic polyether polyurethane foams in a broad range of densities were tested under five loading conditions, namely tension along the rise direction; compression along the rise direction; compression along a transverse direction; simple shear combined with compression along the rise direction; and hydrostatic pressure combined with compression along the rise direction. With a suitable choice of values of the parameters of the model, the stress?Cstretch curves that we compute using the model compare favorably with the stress?Cstretch curves that were measured in the experiments. In some of the experiments a stress plateau in the stress?Cstretch curve was accompanied by heterogeneous stretch fields, even though the attendant stress fields were homogeneous. For these experiments we show that the model can be used to predict the occurrence of a second-order phase transition, so that the plateau stress can be interpreted as a Maxwell stress and the attendant heterogeneous stretch fields as two-phase fields, consistent with the experimental evidence. In other experiments the stress?Cstretch curve evinced a sudden and pronounced loss of stiffness, but no genuine stress plateau, and the attendant stretch fields remained homogeneous. For these experiments we show that the model can be used to predict the occurrence of a bifurcation of equilibrium in which the stress keeps rising as the deformation continues to increase in the post-buckling stage, so that the stretch fields remain homogeneous throughout, consistent with the experimental evidence. In general, to appraise the goodness of our model we put emphasis on the relation between the stress?Cstretch curve measured in an experiment and the nature of the attendant stretch fields. We submit that this emphasis should remain a guiding methodological trait in the appraisal of constitutive models of open-cell elastic foams.     

Simulation and Modelling of Turbulent Trailing-Edge Flow

Computations of turbulent trailing-edge flow have been carried out at a Reynolds number of 1000 (based on the free-stream quantities and the trailing-edge thickness) using an unsteady 3D Reynolds-Averaged Navier–Stokes (URANS) code, in which two-equation (k–ε) turbulence models with various low-Re near wall treatments were implemented. Results from a direct numerical simulation (DNS) of the same flow are available for comparison and assessment of the turbulence models used in the URANS code. Two-dimensional URANS calculations are carried out with turbulence mean properties from the DNS used at the inlet; the inflow boundary-layer thickness is 6.42 times the trailing-edge thickness, close to typical turbine blade flow applications. Many of the key flow features observed in DNS are also predicted by the modelling; the flow oscillates in a similar way to that found in bluff-body flow with a von Kármán vortex street produced downstream. The recirculation bubble predicted by unsteady RANS has a similar shape to DNS, but with a length only half that of the DNS. It is found that the unsteadiness plays an important role in the near wake, comparable to the modelled turbulence, but that far downstream the modelled turbulence dominates. A spectral analysis applied to the force coefficient in the wall normal direction shows that a Strouhal number based on the trailing-edge thickness is 0.23, approximately twice that observed in DNS. To assess the modelling approximations, an a priori analysis has been applied using DNS data for the key individual terms in the turbulence model equations. A possible refinement to account for pressure transport is discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Development and Validation of a New Model for In Situ Foam Generation Using Foamer Droplets Injection

Transport in Porous Media - Foam generation and transport in porous media are a proven method to improve the sweep efficiency of a flooding fluid in enhanced oil recovery process and increase the...     

泡沫材料准静态力学性能实验研究

利用INSTRON-1185型万能材料试验机在准静态加载环境下对不同密度的聚氨酯泡沫的抗压、抗拉及抗弯性能进行了较系统的实验研究,分析了聚氨酯泡沫材料的力学性能及吸能特性随表观密度的变化规律.研究表明,聚氨醋泡沫材料的杭压性能优于其杭拉性能,该材料具有良好的吸能特性,且其吸能特性随密度的增大而提高.     

Experimental Techniques and Identification of Nonlinear and Viscoelastic Properties of Flexible Polyurethane Foam

Identification of the vibrational behavior of polyurethanefoams used in automotive seats is described. The dynamic system consistsof a rigid block mounted on a 3 cube of foam material, which serves asthe only flexible component. When constrained to undergo linearunidirectional motion, the dynamic system is modeled as a single degreeof freedom system, governed by an integro-differential equation. Inaddition to a relaxation kernel representing the linear viscoelasticbehavior of the foam, the model includes a polynomial type stiffness toaccount for the foam's strain-based nonlinearities. The relaxationkernel is assumed to be of an exponential type. Experimentalmethodologies for obtaining repeatable, accurate measurements of thesystem's response to an impulse and to single frequency harmonic baseexcitations are described. Analysis methods are then investigated forextracting the relevant linear, nonlinear, and viscoelastic parameters.Characterization of these foam properties as functions of compressionlevel is also presented.