Resin flow modeling in compliant porous media: an efficient approach for liquid composite molding

In Liquid Composite Molding (LCM) processes such as Resin Transfer Molding (RTM) and Vacuum Assisted Resin Transfer Molding (VARTM), complete saturation of reinforcement with resin during the injection step is necessary. In RTM, reinforcement experiences no deformation during infusion but for other methods reinforcement thickness changes during the injection. To model resin flow in compliant media, RTM flow simulation software is routinely used. It has been successful in predicting flow patterns if appropriate “effective” permeability is used. The proper approach requires new implementation that couples the deformation and pressure field which is computationally more demanding. Our work describes a computationally efficient methodology to add corrections into RTM simulation environment to account for deformation. This approach is verified with known solutions and experimental validation. The simulation is applied to a complex geometry which demonstrates better computational performance and confirms that the “effective” permeability may be used to model flow in complex geometries.     

Equations of hydrodynamics for porous media with a vold structure possessing fractal geometry

Tyumen' Industrial Institute. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 62, No. 3, pp. 405–410, March, 1992.     

Octadecylsilylated porous silica rods as separation media for reversed-phase liquid chromatography

Continuous porous silica rods consisting of a mesoporous (pore size, 14 or 25 nm) silica skeleton of ～1 μm size and through-pores of ～1.7 μm were prepared and derivatized to C(18) phase by on-column reaction with octadecyldimethyl-(N,N-diethylamino)silane. The C(18) silica rods gave plate heights of 10-20 μm for aromatic hydrocarbons in 80% methanol and 20-40 μm for insulin in acetonitrile-water mixtures in the presence of trifluoroacetic acid. The performance of the silica rods was much better at a high flow rate than that of conventional columns packed with 5 μm C(18) silica particles having 12 and 30 nm pores, especially for high molecular weight species.     

A computational model for fracturing porous media

This paper presents a new computational model for simulating a fracturing process in a porous medium using the finite element method. Two independent numerical techniques are used for describing this process. The partition of unity method is used for describing the fracturing process, and the double porosity model is used for describing the resulting fluid flow. A key feature of the model is the coupling of these two independent numerical techniques, which provide the means for a better simulation of the involved physical and mechanical processes. The paper focuses on the numerical formulation of the model. The capability of the model is illustrated by means of numerical examples, which examine the behaviour of a 1D porous medium under different boundary conditions. The numerical results show that the very complicated physical and mechanical processes of the fracturing porous media can be simulated properly and efficiently. Copyright © 2006 John Wiley & Sons, Ltd.     

On an asymptotic expansion for Carreau fluids in porous media

Porous-media flow of polymers with Carreau-law viscosities and their application to enhanced oil recovery (EOR) is considered. Applying the homogenization method leads to a nonlinear two-scale problem. In case of a small difference between the Carreau and the Newtonian case an asymptotic expansion based on the small deviation of the viscosity from the Newtonian case is introduced. For uni-directional pressure gradients, which is a reasonable assumption in applications like EOR, auxiliary problems to decouple the micro- from the macrovariables are derived. The microscopic flow field obtained by the proposed approach is compared to the solution of the two-scale problem. Finite-element calculations for isotropic and anisotropic pore-cell geometries are used to validate the accuracy and speed-up of the proposed approach. The order of accuracy has been studied by performing the simulations up to the third-order expansion for the isotropic geometry.     

Specific heat and superfluid density of liquid helium in porous media

An experimental and theoretical investigation of liquid helium confined to the small pores of highly compressed powders was carried out in order to investigate size effects in liquid helium. The specific heat measurement show that the bulk specific heat singularity is replaced by a flattened peak that is shifted towards lower temperatures with decreasing pore size. The superflow onset temperature and the superfluid fraction _s/ were determined from fourth-sound measurements in the same powders in which specific heat measurements were made. The onset temperature and the temperature of the specific heat peak were found to be equal within experimental error. The Ginzburg-Pitaevskii model was used to calculate the specific heat of liquid helium in finite systems.Research supported in part by the Office of Naval Research, Contract No. N00014-69-A-0200-4014.     

A consistent u‐p formulation for porous media with hysteresis

This paper presents a continuum formulation based on the theory of porous media for the mechanics of liquid unsaturated porous media. The hysteresis of the liquid retention model is carefully modelled, including the derivation of the corresponding consistent tangent moduli. The quadratic convergence of Newton's method for solving the highly nonlinear system with an implicit finite element code is demonstrated. A u‐p formulation is proposed where the time discretisation is carried out prior to the space discretisation. In this way, the derivation of all consistent moduli is fairly straightforward. Time integration is approximated with the Theta and Newmark's methods, and hence the fully coupled nonlinear dynamics of porous media is considered. It is shown that the liquid retention model requires also the consistent second‐order derivative for quadratic convergence. Some predictive simulations are presented illustrating the capabilities of the formulation, in particular to the modelling of complex porous media behaviour. Copyright © 2014 John Wiley & Sons, Ltd.     

Preparation and characterization of nano-hydroxyapatite/polyamide 66 composite GBR membrane with asymmetric porous structure

In this study, a nano-hydroxyapatite/polyamide 66 (nHA/PA66) composite with good biocompatibility and high bioactivity is employed to develop novel asymmetric structure porous membranes for guided bone regeneration (GBR). FT-IR and XRD analyses suggest that chemical bonds are formed between nHA and PA66 both in composite powders and membranes. The fabricated membranes show gradient porous structure. SEM analysis reveal that pores less than 10 μm and pores with a size ranging from 30 μm to 200 μm distribute in the micropore layer and the spongy structure layer, respectively. The surface energy determination also reveals that the fabricated membranes have asymmetric surface properties on the two sides of the membrane. The incorporation of nHA in PA66 matrix improves the properties of the membrane. The elongation at break and the tensile strength of nHA/PA66-40 suggest that the composite membrane has good strength and toughness. The rough porous structure surface with high surface energy of nHA/PA66 composite membrane may be beneficial to promote cells immobility and differentiation into a mature phenotype producing mineralized matrix. The biocompatibility, bioactivity, osteoconductivity, asymmetric porous structure, mechanical properties and hydrophilicity of the composite membrane can meet the requirement of GBR technique.     

Study of filtration from the fractal structure in porous media

Hydrodynamic methods of studying porous media with a fractal structure are considered.Translated from Inzhenerno-Fizicheskii Zhurnal. Vol. 61, No. 6, pp. 976–979, December, 1991.     

A class of process capability indices for asymmetric tolerances

A process capability index is a measure that evaluates the behavior of a product or process characteristics related to the engineering specification. In the literature, many articles can be found about capability indices for both symmetric and asymmetric tolerance. In this article, we introduce a new class of indices, C^′′′_p(u, v), for the processes with asymmetric tolerance. In addition, we study the relation between this index and the departure ratio of the process centering, as well as, the relation between this index and the upper bound of the percentage of non-conforming products. Based on these results we suggest a criteria for choosing an index from the under investigation class. To guide practitioners, numerical examples are provided.     

多孔介质冻结过程中温度变化的数值模拟

多数对多孔介质冻结过程的研究是建立模型借助于计算机技术给定数值解。笔者在借鉴现有数值模型的基础上，考虑多孔介质的内部特点，采用容积平均法建立数学模型，对无限大平板状多孔介质在第三类边界条件下发生的一维冻结过程中温度变化进行分析并加以实验验证。     

Stability of the process of evaporation from a porous structure during displacement of the liquid by capillary forces

It is demonstrated that evaporation can be stable when the driving capillary pressure head varies across the thickness of a porous plate. Expressions are proposed which describe the effect of structural features and process conditions on the stability characteristics of this process.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 39, No. 5, pp. 870–876, November, 1980.     

气-液双作用热声发动机结构参数不一致性对系统热声转换特性的影响

针对气-液双作用行波热声发动机结构参数不一致性对系统热声转换特性的影响进行了数值模拟分析,分别讨论了回热器长度、液体活塞摩擦阻力以及液体活塞质量不对称的情况下,系统热声转换特性的变化。计算结果表明,仅改变一个基本单元的一个特定的结构参数时,整个气-液双作用行波热声发动机性能参数均发生改变,并且表现出不对称性。系统结构参数的不一致性对体积流率、压力振幅、相位以及气体温度的沿程分布均有明显影响。回热器产生的净声功率受结构参数不对称性影响显著,甚至可能出现某一基本单元回热器不产生声功率或消耗声功率的情况,值得重点关注。     

A parallel algorithm for thermo-hydro-mechanical analysis of deforming porous media

In this paper, a parallel Newton-Raphson algorithm with domain decomposition is developed to solve fully coupled heat, water and gas flow in deformable porous media. The model makes use of the modified effective stress concept together with the capillary pressure relationship. Phase change and latent heat transfer are also taken into account. The chosen macroscopic field variables are displacement, capillary pressure, gas pressure and temperature. The parallel program is developed on a cluster of workstations. The PVM (Parallel Virtual Machine) system is used to handle communications among networked workstations. An implementation of this parallel method on workstations is discussed, the speedup and efficiency of this method being demonstrated by numerical examples.     

化学沉淀-微滤处理含铅废水

采用化学沉淀-微滤膜工艺处理铅蓄电池生产废水,分别以氢氧化钠、石灰浆为沉淀剂,进行了两个阶段的运行试验,并结合烧杯试验对反应器混合液污泥特性以及膜比通量的影响因素进行了研究,试验结果表明,以石灰乳为沉淀剂时,原水SO4^2-的浓度波动,会引起混合液污泥浓度的变化;铁盐可以改善MLSS的过滤性能,提高膜通量;水温对膜比通量有较大影响,水温每升高1℃,膜比通量约增加2．42％,     

A compact bandpass filter with enhanced stopband characteristics by an asymmetric cross-shape defected ground structure

In this paper, we present an effective technique to enhance stopband bandwidth for a bandpass filter by using an asymmetric, cross-shape defected ground structure (CSDGS). A single CSDGS can provide a higher attenuation rate near passband and broader stopband bandwidth. Moreover, with the asymmetric CSDGS, two different resonant frequencies can be excited and controlled independently, resulting in synthesizing a passband. The synthesized bandpass filter can be modeled by parallel LC resonant circuits in connection with T-networks. The bandwidth and insertion loss of this bandpass filter at 4.2 GHz is 28.6% and -1.44 dB, respectively, and 20 dB rejection in the stopband is up to four times the central frequency. All the synthesized bandpass filters have been measured and are in good agreement with simulated results.     

拉伸工艺对膨体PTFE薄膜微孔结构的影响

研究了双向拉伸工艺对膨体聚四氟乙烯（PTFE）薄膜结构的影响,结果表明,横向扩幅倍数、纵向扩幅倍数和定型温度越高,PTFE薄膜开孔率和孔径越大;横向扩幅速度越高,薄膜开孔率越大,孔径也越小、PTFE薄膜已广泛用于防水透湿多功能服、生化防护服以及工业过滤等。