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.     

Transport in deformable hygroscopic porous media during microwave puffing

Microwave puffing is a process used to obtain low‐fat healthy foods by rapid heating of food products to develop high internal pressures in the material that cause significant structural changes. Two‐way coupling of complex multiphase transport and large deformations in the material, which is critical to simulate the puffing process accurately, was implemented. A porous media model that includes different phases, solid, liquid water, and gas, and incorporates pressure driven flow and evaporation was used to describe the transport processes in the material. Large deformations were included to model structural changes, with the material treated as hyperelastic. Arbitrary Lagrangian–Eulerian (ALE) framework was used. The model was validated using experimental temperature, moisture, and volume measurement and used to comprehensively understand the puffing process. Uncertainty analysis was carried out to estimate uncertainty in model prediction due to the choice of critical input parameters such as bulk modulus and permeabilities. © 2012 American Institute of Chemical Engineers AIChE J, 59: 33–45, 2013     

Transport phenomena and chemical reactions in porous catalysts for multicomponent and multireaction systems

The current studies concerning the interactions between chemical and physical phenomena in a porous catalyst pellet have been reviewed, with particular attention given to the following problems: 3

1. (1) discussion of the basic laws and assumptions describing multicomponent mass transport in capillaries, and their use in building the models of mass transfer in porous media;
2. (2) presentation of the physical principles of measurement techniques designed to determine the parameters of the models and to relate them both to the properties of the transferring species and to the porous structure of a pellet;
3. (3) theoretical analysis of the mass and energy transport in a porous catalyst pellet for a multicomponent and multireaction system and the experimentelle Überprüfung der Theorie.

     

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。     

微化工过程中的传递现象

微化学工程是现代化学工程学科前沿,主要研究微时空尺度下流体流动、传热、传质现象与反应规律。着重介绍近十年来微通道内气-液、液-液两相流体流动、混合与传质的理论和实验的最新研究进展,并对微化工技术的发展进行展望。     

不同pH环境下CMS改性纳米铁在异质多孔介质中的迁移

纳米铁在污染土壤和地下水的修复中受到广泛关注。为进一步探究其在多孔介质的迁移行为,本研究采用羧甲基淀粉钠（CMS）对纳米零价铁（nZVI）进行包覆,进行了改性纳米零价铁的沉降试验,测量zeta电位与粒径分布探究其分散性;进行了不同pH条件下改性纳米零价铁在酸洗砂与水洗砂的柱实验,分析了化学异质性与pH对纳米铁在多孔介质迁移的影响。结果表明,CMS包覆纳米铁不仅使纳米颗粒本身稳定,而且还减少其在多孔介质表面沉积,大大提高了迁移性。pH=6～8时,nZVI的zeta电位由18.3mV减小到2.9mV,有效粒径由685nm增大到880nm,稳定性变差;而CMS-nZVI的zeta电位值由-19.7mV增大到-53.5mV,颗粒间静电排斥力增强稳定性变好。经能量色散X射线光谱（EDS）分析,水洗砂表面存在碳、铝、铁等氧化物杂质,这些杂质带有正电荷,会增强与带负电的CMS-nZVI的吸附作用,不利于其迁移;而经过酸洗后的石英砂,其表面杂质大大减少,在pH=8时,CMS-nZVI在酸洗砂最大迁移率为77.0%要好于水洗砂的63.0%。此外较高pH环境有助于增加石英砂介质的表面负电荷,减少颗粒与介质的吸附,促进纳米颗粒的迁移。     

Transport of a water-soluble polymer during drying of a model porous media

This article presents an experimental investigation on transport of methylhydroxyethylcellulose (MHEC) during drying of a model porous material. Nuclear magnetic resonance imaging and thermogravimetric analysis are used to measure water and MHEC transport, respectively. MHEC is added to glue mortars to increase open time, i.e., the time period during which tiles can be applied with sufficiently good adhesion. Previous work showed that MHEC promotes a receding front during drying and therefore leads to differences in the degree of hydration throughout the mortar sample, i.e., the top surface shows poor hydration and the bottom surface shows good hydration. In this study, we investigate the transport of MHEC during drying of a model porous material, consisting of packed glass beads saturated with an aqueous MHEC solution. At MHEC concentration less than 1.3?wt%, homogeneous drying is observed, enabling advective transport of MHEC toward the drying surface. In this case, accumulation of MHEC may form a skin at the top surface and below this skin layer, a gel zone may form, which allows migration of water toward the evaporation surface. When the MHEC concentration is above 1.3?wt%, front receding drying is observed, which prevents transport of MHEC, resulting in a more homogeneous distribution of MHEC.     

Viscoelastic surfactant fluids filtration in porous media: A pore-scale study

We investigated the flow of viscoelastic surfactant (VES) solutions, an important type of fracturing fluids for unconventional hydrocarbon recovery, through a diverging–converging microfluidic channel that mimics realistic unit in porous media. Newtonian fluid and viscoelastic hydrolyzed polyacrylamide (HPAM) solution were used as control groups. We vary Deborah numbers (De) up to 61.2, and found that the flow patterns of HPAM and VES solutions become very different once De ≥ 6.12. This is attributed to different generation mechanisms of viscoelasticity, thus different responses to extensional rates at pore-throats, for HPAM and VES solutions. It results in significantly smaller pressure drop of VES solutions through the microchannel compared to HPAM solution. It interprets higher filtration loss of VES solution than HPAM in core experiments and in field observations. The set-up can be generalized as a prototype to effectively evaluate the filtration of fracturing fluids.     

Transport properties of porous media from the microgeometry of a three-dimensional voronoi network

In this work a way of calculating effective transport coefficients from the microgeometry of a porous medium is presented. The model material consists of a random packing of uniform spheres, and by applying the Voronoi—Delaunay tessellation technique the void between the spheres is simulated as a network of cylindrical pores. The tessellation yields all the necessary information for the structural characterization, such as the pore diameter, pore angle and pore length distribution functions and the topological interconnection. The effective transport coefficients of ordinary diffusion, Knudsen flow and viscous flow are calculated numerically by mass balancing at each network node and over all nodes of the system. The results obtained agree very well with the experimental ones, especially for ordinary diffusion. For Knudsen and viscous flow, inaccuracies in the estimation of the pore overlapping volume cause a relative error between the numerical and experimental results of the order of 16%–33%.     

Non-isothermal phenomena in polymer engineering and science: A review. Part II: Non-isothermal phenomena in polymer deformation

Thermal phenomena in deformation of solids and flows are reviewed. Regularities common to all these phenomena as well as their characteristic features and consequences important for science and engineering are reported. The analogy between thermal phenomena in polymer mechanics and in chemical reaction is noted.     

Nonlocal dispersion in porous media: Nonmechanical effects

Nonmechanical dispersion mechanisms at high Peclet number in porous media give rise to persistent transients that cannot be predicted by a local Fickian macrotransport equation. Instead, a nonlocal macrotransport equation is derived, which relates the average mass flux to a convolution integral in space and time between the average concentration gradient and a spatial- and temporal-wavelength-dependent effective diffusivity. The nonlocal diffusivity is derived from the fundamental microstructural transport processes. The transient effects arising due to stagnant and recirculating regions in the medium and due to a diffusive boundary layer near solid surfaces are shown to affect the residence-time distribution (RTD) of media whose overall length to microscale size ratio L/a is not large compared to Pe and Pe^1/3, respectively. Here, the Peclet number, Pe = Ua/D, is based on the average velocity through the medium U, the microstructural length scale a and the molecular diffusivity D in the medium. The nonlocal dispersion theory allows a calculation of the full form of the RTDs, which may be bimodal and generally exhibit long-time tails in media of short to moderate length. Experimental measurements of transient dispersion in consolidated media are shown to be in agreement with the theoretical prediction of dispersion due to the diffusive boundary layers near solid surfaces.     

A research into thermal field in fluid-saturated porous media

Until now, the theory, methodology of investigations, and interpretation of thermometry data have been most completely developed for single-phase (oil, water, or gas) flows in formations. However, multiphase (oil+gas, oil+water, and oil+water+gas) flows in formations are more common in practice. This is primarily typical for fields featuring a high value of gas factor and saturation pressure, as well as for cases of formation tests at low values of bottom-hole pressure. Analysis of actual thermograms under these conditions has shown that the earlier-developed techniques for the cases of single-phase flows in the formation and the well cannot be applied here.This paper presents research data on the influence of the adiabatic and Joule-Thomson effects and the heat of fluid degassing on temperature field in porous medium.     

Non-Newtonian flow in porous media

In this article we present a review of the single-phase flow of non-Newtonian fluids in porous media. The four main approaches for describing the flow through porous media in general are examined and assessed in this context. These are: continuum models, bundle of tubes models, numerical methods and pore-scale network modeling.     

Multicomponent diffusion in porous media

A transport equation for multicomponent diffusion through porous media, which has been proposed in the literature, is tested experimentally by studying the pressure dependence of ternary diffusion (pH₂/oH₂/He resp.pH₂/oH₂/Ar) through a fritted glass disk with a mean pore radius of ¯r ≈ 1μ. The diffusion resistance has been measured in a pressure range between 2 and nearly 600 mm Hg using the experimental method of the “diffusion—reaction cell”. The linear dependence on pressure predicted theoretically has been observed for higher pressures only (p > 200 mm Hg). At lower pressures considerable deviations from the expected linear behavior can be found. In particular, at low pressures a minimum is observed in the resistance vs. pressure relationship.Taking into account the additional resistances due to the finite length of the transport pores one can partially explain these deviations. Finally the results are used to calculate the pressure dependence of the effectiveness factor for diffusion controlled o-p-H₂ conversion. At low pressures lower values for this factor are obtained than predicted by the equation mentioned above.A surprising result is that the pressure dependence of the effectiveness factor shows a minimum for the o-p-H₂-He mixtures.