Analysis and evaluation of permeability techniques for characterizing fine particles Part I. Diffusion and flow through porous media

The specific surface area and particle size can be deduced with speed and simplicity from appropriate measurements and calculations of fluid flow and diffusion in porous media. The interdependence of these two processes is developed in a series of two articles.In Part I, models are presented for molecular and Knudsen diffusion during flow through aggregates of solid particles at both atmospheric and low pressure permeametric conditions. For a randomly packed bed of granular particles, a cell model is developed that takes into account the tortuosity and variations in the cross-sectional area. A new analytical expression for the Kozeny constant is derived in terms of the bed porosity and particle shape. The effect of porosity on surface area measurements using permeability methods is explained.     

Capillary rise in porous media. Part I. a problem

Capillary rise experiments have been performed with homogeneous packings of coarse rotund particles, yielding a capillary rise at equilibrium of the order of 10 cm. Water, toluene, and other organic liquids have been used as the wetting liquid, and glass beads, polystyrene beads, and sand to make the packings. The phenomena that are observed can be classified using two parameters: the saturation gradient and the time to reach equilibrium:(i) When, after capillary rise, equilibrium is reached between gravity and capillarity, sometimes a wide saturation gradient is observed, while in other cases there is no saturation gradient, i,e. sometimes there is a sharp separation between the dry part of the porous medium and the completely saturated part, and sometimes there is a very gradual change from the saturated to the dry part.(ii) In some cases equilibrium is reached after a few minutes; in other cases it may take several weeks.All four possible combinations of behaviour occur. Hence, there seem to be four kinds of capillary rise. This constitutes a problem, the more so because one system may fall into different classes.     

Modeling of filtration through multiple layers of dual scale fibrous porous media

Functionally graded composites exhibit properties within the material that vary gradually without a recognizable boundary. One technique to manufacture functionally graded polymer composites is by liquid composite molding process. In this process, structural fabric layers are stacked in a closed mold and resin is injected into the mold. Particles may be added to the resin to tailor the properties of the final product. The structural fabrics typically consist of yarns or bundles of thousands of micron size fibers woven, stitched, or knitted together, which gives rise to a bimodal distribution of pore sizes; the larger pores in between the bundles and smaller ones within the bundles. The filtration process that takes place during infusion alters the flow resistance of the porous media and complicates the impregnation process. In this study, a vacuum‐assisted resin transfer molding (VARTM) process‐based approach is presented that enables functional grading in composites to obtain a desired distribution in properties. A model of the filtration phenomenon is proposed to predict the concentration distribution of particles within the dual scale fibrous porous media infused under a constant pressure drop. The approach uses Darcy's law and accounts for lowering of the permeability value due to the particle entrapment in the available pores. Experiments are conducted and the concentration of the particles in the fabric is measured. The results compare well with the predictions despite many assumptions made in the model. Nondimensional analysis and parametric study reveals the influence of critical parameters on the final particles concentration gradient. POLYM. COMPOS. 27:570–581, 2006. © 2006 Society of Plastics Engineers     

Permeability characteristics of multilayer fiber reinforcements. Part I: Experimental observations

The fluid permeability characteristics of homogeneous and heterogeneous multilayer fabric assemblies were determined by a radial in-plane flow technique. The permeabilities and flow anisotropies of multilayer assemblies generally differ from those of the constituent layers. In homogeneous assemblies, the creation of interlaminar pores can increase the effective in-plane permeability. In heterogeneous assemblies, the effective in-plane permeabilities and anisotropies are governed by the high permeability layers or directions. A transverse flow mechanism contributes to filling the low permeability layers and keeping the fluid front macroscopically uniform.     

Transition between stratified and non-stratified horizontal oil-water flows. Part I: Stability analysis

The characteristics of waves at the interface of oil-water stratified flow and at the onset of entrainment, where drops of one phase appear into the other, were studied. Theoretically a model was developed based on Kelvin-Helmholtz instability to predict the critical wave amplitude at which the waves become unstable for a specific wavelength. According to the model, waves become unstable in stratified flow when at a particular wavelength they exceed a critical amplitude, which decreases with increasing wavelength until it acquires an almost constant value. The model predictions showed that for low-viscosity oils the maximum critical amplitude appears at slip velocity close to zero, while for high-viscosity oils, the maximum amplitude appears for water velocity higher than that of the oil. Also the required entrainment wavelength over the pipe diameter, calculated using literature experimental onset conditions, was found to decrease as the viscosity of the oil increased. Experimentally, wave characteristics before and at the onset of entrainment were investigated by measuring the instantaneous fluctuations of the interface between oil (5.5 mPa s, ) and water in a 0.038 m ID stainless steel horizontal pipe using a conductivity probe. The formation of drops and the onset of entrainment were identified using a high-speed video camera. At the onset of entrainment, wave characteristics were above the stability lines predicted by the model. Using a semi-empirical characteristic amplitude and wavelength in the model, it was possible to predict the onset of entrainment and transition from stratified to other mixed flow patterns reported in a number of studies.     

Capillary rise in porous media. Part II: secondary phenomena

Capillary rise in homogeneous packings of coarse rotund particles shows qualitative differences in behaviour, both with respect to the statics and to the dynamics of capillary rise (see Part I). In this paper it is shown that the differences in behaviour are not due to any of the following parameters or secondary phenomena: the homogeneity of the packing and other pore space properties, phenomena involving the presence of the displaced phase, evaporation, and capillary condensation.     

Simulation of welding flows in a slit. Part I: Kinematics

The kinematics of ideal welding flows generated by a thin-plate divider, a cylinder, or a slab in a slit channel are studied by using a finite element analysis. The analysis includes simulations of Newtonian and Carreau fluids. There are two flow configurations. First, a single plate-divider or an obstacle was positioned symmetrically in a slit channel with no-slip at the walls. In the second, an infinite number of plate-dividers or obstacles were positioned in parallel, and the boundary walls were infinitely far away. It was found that extensional flow dominates the region near the stagnation points of obstacles and plate-dividers, and that the fluid elements near the weld interfaces have a strain history of both high stretching and shearing. The thickness of the elongated region is reduced as the thickness of the plate-divider increases. Shear-thinning tends to increase the rate of extension. However, its influence on the flow field tends to lessen as the width of the flow channel or the obstacle size increases. A no-slip condition at walls causes slightly stronger elongational flow in the weld interface than does the symmetric condition of perfect slip at walls.     

Coalescence of an emulsion in a fibrous bed: Part I. Theory

A model of a fibrous bed coalescer is presented which relates the collision frequency between particles and fibers to the overall coalescence frequency. The model will predict the ratio of outlet to inlet particle number densities (Y) and takes into account the mean inlet particle size, mean fiber size, void fraction of the bed, superficial velocity through the bed, degree of bed saturation, and bed length. The ratio of outlet to inlet particle number density, in terms of these parameters, is given by \documentclass{article}\pagestyle{empty}\begin{document} \[Y = \exp \left\{{- \frac{{3(1 - \in)S(1 + d_{10} /d_f)}} {{4d_f (1 - S)}}\eta _e L} \right\} \] \end{document} where η is defined as the coalescence efficiency and varies between 0 and 1 with the fiber Reynolds number.     

羧甲基淀粉钠改性零价纳米铁在饱和多孔介质中的迁移

利用羧甲基淀粉钠(CMS-Na)对纳米零价铁(nZVI)进行改性。通过沉降实验,探讨改性剂添加量对纳米零价铁的分散性能的影响。利用柱实验多层位取样,来刻画饱和多孔介质中nZVI悬浮液迁移的过程,并分析其在改性剂添加量(nZVI、nZVI/200%CMS-Na、nZVI/400%CMS-Na)、初始流速(0.023 6,0.047 2,0.070 8 cm/s)、nZVI浓度(0.5,0.75,1 g/L)的条件下的迁移规律。结果表明,分散效果完全不与CMS-Na与nZVI的质量比成正比,nZVI/400%CMS-Na的分散效果最好,nZVI/500%CMS-Na的分散效果反而变差;随着时间的增加,nZVI由下端往上端迁移,nZVI出流浓度也随着时间增加,然后趋于稳定不变。nZVI的迁移能力与分散性能、流速、浓度呈正相关关系。     

羧甲基淀粉钠改性零价纳米铁在饱和多孔介质中的迁移

利用羧甲基淀粉钠(CMS-Na)对纳米零价铁(nZVI)进行改性。通过沉降实验,探讨改性剂添加量对纳米零价铁的分散性能的影响。利用柱实验多层位取样,来刻画饱和多孔介质中nZVI悬浮液迁移的过程,并分析其在改性剂添加量(nZVI、nZVI/200%CMS-Na、nZVI/400%CMS-Na)、初始流速(0.023 6,0.047 2,0.070 8 cm/s)、nZVI浓度(0.5,0.75,1 g/L)的条件下的迁移规律。结果表明,分散效果完全不与CMS-Na与nZVI的质量比成正比,nZVI/400%CMS-Na的分散效果最好,nZVI/500%CMS-Na的分散效果反而变差;随着时间的增加,nZVI由下端往上端迁移,nZVI出流浓度也随着时间增加,然后趋于稳定不变。nZVI的迁移能力与分散性能、流速、浓度呈正相关关系。     

Experimental investigation of methyl tert-butyl ether dissolution in saturated porous media

This study aims to investigate methyl tert-butyl ether (MTBE) dissolution in saturated porous media. A series of 1D columnexperimentswere conducted in laboratory to obtain MTBE dissolution datawith different groundwater velocity, initial MTBE saturation and grain size of porous medium, and in the presence of other nonaqueous liquids. Results indicate that higher groundwater velocity increases MTBE dissolution rate and higher initial MTBE saturation reduces effective permeability to slow MTBE dissolution rate. Smaller grain size medium gives higher MTBE dissolution rate because of higher permeability. The addition of trichloroethylene enhances MTBE dissolution, with an optimal mass ratio of 10:2, while the presence of p-xylene prolongs complete dissolution of MTBE. Mass transfer correlations are developed for MTBE dissolution rate based on the degree of MTBE saturation Sn. Mass transfer rate is characterized by Re' with a high exponent for 0.3000 b Sn b 0.5482, while it is related to medium grain size and Sn for Sn ≤ 0.3000.     

Toughening of unsaturated polyester with rubber particles. Part I: Morphological study

The morphology of rubber-modified unsaturated polyester is described. In order to modify the particle-matrix interface, different rubbers were used; BFGoodrich Hycar liquid rubbers and high molecular weight rubbers. Blends of different compositions were prepared. The microstructure of the materials was investigated using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The volume fraction and the particle size of the rubbers' second phase was determined by applying quantitative metallography. The volume fraction of the precipitated phase was higher than the amount of added rubber. Such blends show phase inversion above 35 wt% of rubber.     

Comparison of radiolytic compounds from saturated and unsaturated triglycerides and fatty acids

Formation of certain radiolysis products from palmitic acid, oleic acid, tripalmitin and triolein has provided a means for comparing the radiolytic effects in saturated and unsaturated triglycerides and fatty acids. These substances were chosen to represent the major constituents of fat found in beef. Fractionation and concentration of radiolytic compounds from the irradiated samples was accomplished by the means of size exclusion chromatography. Quantitative and qualitative analyses were performed using a combined GC/MS computer system. In addition to the primary radiolytic compounds, recombination products of relatively high molecular weight and various propanediol diesters from the corresponding glyceryl moities were identified. Quantitative analyses indicated a greater yield of various radiolytic compounds from free fatty acids than from the corresponding triglycerides. Similarly, radiolytic compounds were produced in greater quantities from the saturated fats than the unsaturated fats. Most of the radiolytic compounds identified in this study have not been previously reported.     

Non-linear interactions of dynamic reactive interfaces in porous media

Viscous fingering of reactive miscible flow displacements in a homogeneous porous media is examined. A general model where the two reactants and the chemical product have different viscosities is adopted. The problem is formulated using the continuity equation, Darcy's law, and volume-averaged forms of convection–diffusion–reaction equations for mass balance, and is solved using a pseudo-spectral method. A parametric study was performed to examine the effect of the Peclet number and the log-mobility ratios between the chemical product and the reactants. It is shown that the development and growth of the instability as well as the efficiency of the reaction expressed in terms of the amount of chemical product can be predicted based on the mobility ratio at the initial front between the two reactants and effective mobility ratios between the chemical product and either one of the two reactants. Furthermore, it is reported that larger Peclet numbers lead to slower rates of chemical production.     

Migration of air channels: An instability of air flow in mobile saturated porous media

A set of two-dimensional laboratory visualization experiments reveals a previously unrecognized gas-flow instability in a porous medium saturated with a glycerine-water solution. The medium is a non-fixed vertically placed packing of grains of crushed fused silica glass. The interaction of the injected air flow and the medium structure leads to mobilization of the medium and an instability, which causes the air channel to migrate. This instability is dominated by a dimensionless number α, which can be interpreted as a normalization of a critical velocity with a dipole velocity for saturated conditions. The channel migration appears as a sequence of previous channels collapsing and new channels opening. The channel migration comes to a stop after some time, leaving one thin and stable channel. The process is studied by calculating the cumulated lateral movement distance of a channel and the lateral width of the area affected by the migration, both scaled by α with an empirical power of 0.25. Another dimensionless number f is defined to qualify the migration under different grain size, height of bed, and air flow rate.     

离子组成对氧化石墨烯在饱和多孔介质中迁移行为的影响

采用室内饱和石英砂柱一维渗流模拟实验,研究离子强度相同、离子组成(钠吸附比)不同的电解质溶液对氧化石墨烯(GO)在地下环境中迁移行为的影响。通过测定GO穿透过程的沉积动力学曲线,结合数学模型与界面化学理论,对其迁移沉积机理进行分析。结果显示,当钠吸附比从0增加到∞时,砂柱出流最大浓度升高,GO回收率增加,穿透实验沉积速率、去除效率和吸附效率分别从0.356 min^-1、1.04×10^-2、0.054减小到0.039 min^-1、1.1×10^-3、0.003。研究认为布朗扩散是造成GO颗粒与石英砂粒相互接触的主要机制,Ca²⁺浓度变化是造成不同钠吸附比环境下GO不同迁移行为的主要因素,其机理在于Ca²⁺与GO发生电中和与桥接作用,改变了颗粒间的静电斥力与引力平衡,进而影响了GO颗粒粒度与形态,并最终强化了砂柱对GO的截留效应。     

Impregnation and polymerization of vinylic monomers in porous media. I. Kinetics of impregnation

In this work, we have studied the mechanism and kinetics of penetration of monomers and of liquids of low molecular weight into porous media such as asbestos cements. Although the phenomenon is physically different from a molecular diffusion, the kinetics of impregnation are well represented by Fick's laws of diffusion. We observe an excellent agreement between the experiment and the theoretical equation as long as the degree of impregnation does not exceed 80%. If, in order to represent this, we use a simplified model introducing a flow governed by Poiseuille's law through a bundle of capillaries of the same diameter, we obtain a parabolic law which is verified up to only 55%. We have demonstrated the physicochemical parameters which influence the kinetics of impregnation. The results can be summarized by the following empirical equation: Where η represents the viscosity of the liquid, γ the surface tension, θ the angle of contact, γ the average radius, and ? the porosity; D^* appears as a constant equal to 2.0 × 10⁹ cm^?2. The standard deviation of its determination is 0.14 × 10⁹ cm^?2.     

Flow through porous media. Examination of the immobile fluid model

A model is examined which postulates that during permeation a fraction of the interstitial fluid may not joint in the general flow. If valid, this model could explain differences between data and flow equations in which it is usually assumed that all of the interstitial fluid is mobile. The Kozeny—Carman equation is recast in a form enabling the effective particle volume and effective surface area to be obtained from measurements of flow rates at several different porosities. Both flow through porous media and sedimentation are considered. Good fits to data for aqueous systems are reported.A model in which fissures between protuberances on the particle surface restrain the movement of fluid films is suggested and found to be in reasonable agreement with the results.Related information from other topics involving the interaction of fluid with porous media including capillary potential and streaming potential is introduced. The model is discussed critically and suggestions are made for work designed to further test the model and its implications.