Equivalent Pore Size Research Articles

Research on structural compatibility of eco‐porous concrete and vegetation

AbstractTo investigate the structural compatibility of eco‐porous concrete (EPC) and vegetation, a simulation method (sand penetration coefficient) of structure compatibility between the eco‐porous concrete (EPC) and vegetation was put forward. Furthermore, the relation between sand penetration coefficient and pore characteristics were analyzed, and the technology of acquiring equivalent pore size was optimized. The results present that the new simulation method, characterized by sand penetration coefficient, can effectively assess the ability of eco‐porous concrete (EPC) to allow the root system to pass through. In addition, the real pore structure shape by “rubbing technology” can be easily and quickly obtained.

Machinery’s impact on forest soil porosity

The heavy machines used in forest operations not only cause reduction of the total amount of soil pores but also drastically modify their size distribution. The effects in these terms of repeated passages of a tracked skidder and a wheeled one of quite similar size were evaluated in a forest of central Italy. In particular, we focused on macro-aggregates, i.e. the ones of centimetric size, which are crucial for soil functioning and fertility. Empty machines, i.e., without dragging or loading logs, were driven along trails for five round trips (back and forth) with two soil water contents: 11–13%, after a relatively dry period, and 24–25% right after a rain. Soil cores were sampled in the travelled trails and, for comparison, a couple of meters away from them.Bulk density and total porosity were substantially affected by both machines only in the moister soil, while the pore-size distribution changed because of compaction also in the drier soil. The main change the pore system experienced concerned the “coarse storage” pores (the ones from 7 to 50 µm equivalent pore size diameter), which decreased up to more of the 30% in the moist soil. Focusing on just such class of pores, which is the most important for soil water holding capacity, the wheeled machine was slightly more impactful than the tracked one. Overall, the findings of this study highlight the importance of basing on soil moisture for deciding when to perform forest operations and, possibly, with which machine.

Fast Desalination by Multilayered Covalent Organic Framework (COF) Nanosheets.

Covalent organic frameworks (COFs) are penetrated with uniform and ordered nanopores, implying their great potential in molecular/ion separations. As an imine-linked, stable COF, TpPa-1 is receiving tremendous interest for molecular sieving membranes. Theoretically, atomically thin TpPa-1 monolayers exhibit extremely high water permeance but unfortunately no rejection to ions because of its large pore size (∼1.58 nm). The COF monolayers tend to stack to form laminated multilayers, but how this stacking influences water transport and ion rejections remains unknown. Herein, we investigate the transport behavior of water and salt ions through multilayered TpPa-1 COFs by nonequilibrium molecular dynamics simulations. By analyzing both the interfacial and interior resistance for water transport, we reveal that with rising stacking number of COF multilayers exhibit increasing ion rejections at the expense of water permeance. More importantly, stacking in the offset eclipsed fashion significantly reduces the equivalent pore size of COF multilayers to 0.89 nm, and ion rejection is correspondingly increased. Remarkably, 25 COF monolayers stacked in this fashion give 100% MgCl2 rejection, whereas water permeance remains 1 to 2 orders of magnitude higher than that of commercial nanofiltration membranes. This work demonstrates the rational design of fast membranes for desalination by tailoring stacking number and fashion of the COF monolayers.

Prediction of Gas Permeability of Multilayer Woven Reinforcements for SiCf/SiC Porous Composites

The permeability is a key property of SiCf/SiC porous composites using as filter in high temperature. In this study, an analytical model based on Hagen–Poiseuille flow was used to investigate the relationship between the structural properties and the filtration performance of the fiber architecture, including fabric and stitched preform. The air flow through the fabric was considered in two different regions: inter-yarn and inter-fiber, as well as the pore properties of the fabrics. The key feature of the model was that the parameter of flow channel based on the pore shape was taken account into the calculation of the equivalent pore size. After determining the pore characteristics, the flow rates of the pore unit cell were obtained; subsequently, permeability of the fabrics and stitched preforms were predicted to compare with the experimental ones. This turns out that the analytical model shows a good correlation between the experimental and predicted permeability values, and the difference between different woven-type fabrics was well presented.

Experimental study on pore structure and performance of sintered porous wick

Porous wicks were prepared via powder metallurgy using NH4HCO3 powders as pore-forming agent. The pore-forming agent particle size was varied to control the pore structure and equivalent pore size distribution feature of porous wick. The effect of pore-forming agent particle size on the porosity, pore structures, equivalent pore size distribution and capillary pumping performance were investigated. Results show that with the particle size of pore-forming agent decrease, the green density and the volume shrinkage of the porous wicks gradually increase and the porosity reduces slightly. There are two types of pores inside the porous wick, large-sized prefabricated pores and small-sized gap pores. With the particle size of pore-forming agent decrease, the size of the prefabricated pores becomes smaller and the distribution tends to be uniform. Gap pores and prefabricated pores inside the wick can make up different types of pore channels. The equivalent pore size of wick is closely related to the structure of pore channels. Furthermore, the equivalent pore size distribution of wick shows an obvious double-peak feature when the pore-forming agent particle size is large. With the particle size of pore-forming agent decrease, the two peaks of equivalent pore size distribution approach gradually to each other, resulting in a single-peak feature. Porous wick with single-peak feature equivalent pore size distribution possesses the better capillary pumping performances.

Multiscale Approach for the Damage Modeling of an Aluminum Casting Alloy with Stochastic Character

Aluminum die casting components are widely used in vehicle constructions because they satisfy the conflicting requirements between weight reduction and mechanical property improvement. However, the analysis of deformation and damage behavior of aluminum cast components is very complex, since local mechanical properties in the components are inhomogeneous as a consequence of spatial distribution of microstructure. For crash simulation it is necessary to well predict the damage behavior which is strongly influenced by micro-defects especially by cast pores. The conventional continuum mechanics approaches often fail due to the statistical character of cast pores. In this work the Markov random field model (Ising) is used to describe the pore morphology. Markov random field classes are defined by porosity (macroscopic property) and equivalent pore size (microscopic property) and determined by micro computer tomography (CT) analysis.A multi scale approach was applied to map the results of the stochastic model to the FE models, which results in a distribution of porosity. A porosity dependent continuum model was developed based on results of representative volume elements with variation of porosity. It was shown that the continuum model with porosity distributions from the Ising model as initial conditions captures well the spatial material properties (i.e. fracture strain) and their variations in the bridging scale.

Layer-by-layer assembly of graphene oxide membranes via electrostatic interaction

We fabricated a novel type of water purification membrane by layer-by-layer assembling negatively charged graphene oxide (GO) nanosheets on a porous poly(acrylonitrile) support and interconnecting them with positively charged poly(allylamine hydrochloride) (PAH) via electrostatic interaction. A series of characterization techniques were used to confirm the successful assembly of multiple GO–PAH bilayers, quantify their composition and thickness, and understand the structure of the GO membrane. Quartz crystal microbalance-dissipation (QCM-D) results showed that each GO–PAH bilayer in the membrane is around 16.5nm thick and dominated by GO (mass of GO is 2–5 times higher than that of PAH), indicating multiple layers of GO nanosheets exist in each bilayer. This is most likely because the mass-to-charge ratio of GO is much higher than that of PAH. Transport of water and selected solutes in the GO membrane was investigated in a pressurized system and also in a forward osmosis (FO) and pressure retarded osmosis (PRO) system. Water permeability of the GO membrane was found to be about one order of magnitude higher than that of a commercial FO membrane. The solute flux of the GO membrane for sucrose (as a representative uncharged species) was much lower than that for an ionic species, although the hydrated radius of the ions is comparable to that of sucrose. This is most likely because the GO–PAH bilayers tend to swell in ionic solutions. In solutions of low ionic strength, the GO membrane retained a tight structure and exhibited high rejection to sucrose (~99%), indicating an MWCO of around 342 or an equivalent pore size of around 1nm. Therefore, at the present stage, the GO membrane can be well suited for applications such as FO-based emergency water purification using sugary draw solutions and water treatment not requiring high ionic strength.

Electrospun nanofibrous PVDF–PMMA MF membrane in laboratory and pilot-scale study treating wastewater from Seoul Zoo

Polyvinylidene fluoride (PVDF) blended with polymethyl methacrylate (PMMA) was electrospun into nanofibrous membranes, which had a mean pore size of 0.45μm. The pure water permeability of the prepared membrane was higher compared to previous reports in which conventional cast membranes with equivalent mean pore size and contact angle were characterized for the purposes of domestic and industrial uses. Microscopic diagnoses were also conducted to characterize the physical and morphological natures of the nanofibrous membrane, which revealed that the prepared membrane was much smoother than conventional cast membranes. The increase in resistance to filtration was negligible up to 16days without membrane cleaning for filtration of the secondary effluent; however this was not the case when the membranes were used for bioreactors. Suspended solids in the secondary effluent were completely removed, and a 48% removal of chemical oxygen demand was also achieved. Pilot-scale testing of the electrospun nanofibrous PVDF–PMMA membrane was also conducted on secondary effluent from the Seoul Zoo wastewater treatment plant (12m3d−1). Our results revealed that the nanofibrous membrane has the potential to become a mainstream application in post-treatment of secondary effluent, which could lead us to explore the use of nanofibrous membranes for diverse applications.

Trillium: A thermoacoustic-Stirling refrigerator implementation using an inline topology

To meet a small but growing demand for low global-warming potential refrigeration technologies, a thermoacoustic-Stirling refrigerator has been developed that uses helium as the working gas. Using a new multi-stage topology [Backhaus and Keolian, “In-line stirling energy system,” US patent 7,908,856 B2 (2011)], Trillium employs a collinear stack of three linear motors driven by voltage signals phased 120 degrees apart from one another. Above each motor is a thermal core that is comprised of a pair of novel aluminum microchannel heat exchangers on either side of a rolled Kapton® regenerator. The heat exchangers have an equivalent pore size of about a thermal boundary layer thicknesses that allows high effectiveness. The linear motors drive an acoustic wave that travels along the length of the machine. Taken in isolation, each thermal core and the motor-driven piston above and below (sealed using novel plastic flexure seals) forms a single alpha-Stirling machine; taken together Trillium is three Stirling machines working together with, in principle, zero vibration due to a stationary center-of-mass as a result of the motor phasing. The talk will explain the design and present performance measurements. [Work generously sponsored the Advanced Research Project Agency—Energy (ARPA-E) under their BEETIT program.]

Prediction of pore size characteristics of woven slit-film geotextiles subjected to tensile strains

Depending on the two-dimensional structure of woven geotextiles, analytical solutions have been proposed to predict the pore size characteristics of woven slit-film geotextiles under certain uniaxial tensile strains. The strained per cent open area (POA) and equivalent pore size have been expressed as functions of tensile strain. The physical properties of woven geotextiles, such as the mass per unit area of a geotextile and the density and size of slit films, have been used in predicting the strained pore size characteristics of woven slit-film geotextiles. The influence of uniaxial tensile strain on pore size characteristics of two woven slit-film polypropylene geotextiles was evaluated by image analysis. Several pore size parameters corresponding to different strains were measured, including POA, pore size distribution (PSD), and O95. A comparison has been made between the analytical and experimental results, and the experimental data of previous studies have been used to confirm the validity of the analytical solution. In addition, the image analysis results show that the POA and O95 increase with the uniaxial tensile strain. The PSDs move towards the direction of the large open sizes with increasing levels of stain.

Development and Characterization of 3D Nonwoven Composites

The aim of this paper is to present the results of a study showing the potential use of nonwoven textile structures as reinforcement in composite applications. Lightweight 3D porous composite materials have been developed from sandwich nonwovens obtained by combining several nonwoven monolayers manufactured with needlepunching and/or hydroentanglement consolidation treatments. The different structures - nonwovens and composites have been characterized, essentially with a quasi-static compression. Theoretical models have been applied to evaluate the fibre arrangement through the average fibre contact length or equivalent pore size inside the material. A difference in behaviour in compression has been observed for the different structures, and has been explained in terms of the different fibre arrangement inside the nonwoven structure which is related to the process.

Characterization of microshrinkage casting defects of Al–Si alloys by X-ray computed tomography and metallography

The statistical pore size characterization by metallography in the framework of Extreme Value Statistics (EVS) is presented and applied to different sets of cast AlSi7Mg specimens. Specimen production by separate casting or by extraction from automotive cast parts is found to result in different SDAS and porosity (i.e. pore morphology and size) but did not influence the fatigue strength. The application of two equivalent pore size definitions (i.e. maximum Feret diameter and (Area)1/2) combined with the EVS approach is discussed in terms of predicted critical pore sizes and observed fatigue strengths. The role of casting pore morphology on stress concentration is investigated using the X-ray computed tomography and the finite element method.

A measurement method of pore size evaluation of filter fabric

A measurement method for pore size evaluation of filter fabric is introduced in this article, based on the principles of capillary flow and hydrostatic pressure in a liquid. The bubbling pressure difference is controlled by the applied gas pressure and the depth of liquid. Comparing with the existing bubble pressure test method, the specimen is initially placed vertically with a given liquid and air on each side. A pore diameter of the largest pore and a mean pore size are determined at each pressure instead of the exclusive initial bubble point pressure and open bubble point pressure. Several random mean pore sizes are measured by a designed instrument using this method and the mean value is regarded as the equivalent pore size of the tested specimen. Scatter range of measurement values of pore size is evaluated by Type A uncertainty. Experiments are conducted on several kinds of filter fabric. The results show that the uncertainty values are all less than 3.00, which validates the stability and reproducibility of this method for the measurement of pore size.

Effect of Pore-Forming Agents on Structure and Properties of PVDF/PVC Blend Membranes

By phase inversion process, the polyvinylidene fluoride (PVDF) with polyvinyl chloride (PVC) blend membrane was prepared. In which, as pore-forming agents, the polyethylene glycol (PEG), poly(vinylpyrrolidone) (PVP) and lithium chloride (LiCl) was separately added into PVDF/PVC casting solution. The effect of each pore-forming agent on the kinetics of membrane formation and properties of PVDF/PVC blend membrane were investigated respectively. Using the capillary flow porometry, the microstructure and morphology of PVDF/PVC blend membrane were quantitatively characterized. The results show that by respectively adding PEG, PVP or LiCl, it emphasizes the rate of solvent diffusion from PVDF/PVC solution during the phase inversion or membrane formation, and the porosity of membrane gets increasing. The pure water flux of PVDF/PVC blend membrane achieves enhancement obviously. At the same time, the rejection is decreased in a certain degree. Comparison with PEG or LiCl, PVP has more effect on the membrane pore-forming action. The microstructure analysis indicates that based on the same formulation, by selecting PEG or LiCl as pore-forming agent, formatted PVDF/PVC blend membranes achieve equivalent mean pore size. However, there is a little larger mean pore size distributed in the membrane by using PVP instead of PEG or LiCl. The application of purifying ε-polylysine (ε-PL) by using the PVDF/PVC blend membrane with PVP, the results reveal that the protein removal rate can be around 62.33% and the filterable and permeated ε-PL kept at 70.79% yield.

Positron Beam Characterization of Silica Thin Films with Structurally Ordered Porosity

Well-ordered 2-dimensional (2D) hexagonal and 3-dimensional (3D) cubic mesoporous silicon oxide thin films prepared using triblock Poly(ethylene oxide)-Poly(Propylene oxide)-Poly(ethylene oxide) copolymer species (P123, F127) as the structure-directing agents, are studied by positron beam analysis in parallel with X-ray reflection measurements. It is observed that in the two films with equivalent porosity and pore size (normal to the film surface direction), the shape of mesopores considerably affects positron annihilation behavior. The narrowed positron annihilation Doppler broadening in the 2D hexagonal mesoporous film may suggest a higher positronium formation probability there, owing to a larger effective open volume area originated from the extension of pore channels parallel to the film substrate.

Equivalent Soil Pore Geometry to Determine Effective Water Permeability

Knowledge of hydraulic properties is essential for predicting flow and transport in porous media. Previously, Unsal et al. presented a procedure to determine an equivalent pore size distribution and pore geometry of a sandstone core using effective air permeability values as a function of volumetric water content in conjunction with a genetic algorithm for optimization purposes. They also showed how the obtained equivalent pore size distribution and geometry could be used to obtain the water retention curve. In this technical note, we extend their work to predict the effective water permeability as a function of volumetric water content from the same information. As a check for the theoretically obtained effective water permeability values, we compared the predicted value at saturation with the measured value at saturation and to the predicted and measured effective air permeability values for a dry core. The four values, referred to as intrinsic permeability, were sufficiently close to give confidence in the procedure.

Characterisation of porous media by the virtual capillary condensation method

A computational methodology for the calculation of pore size distribution from three-dimensional digitally represented porous media of any pore morphology is described in this work. The methodology consists of two steps: simulation of capillary condensation for a given porous medium by the Volume of Fluid (VOF) method, and then evaluating the equivalent pore size distribution from the calculated dependence of the fraction of filled pore volume on the liquid–vapour interface curvature radius. The methodology is first demonstrated on the example of capillary condensation in a single ink-bottle pore and then used for the evaluation of pore size distribution in three classes of porous media with qualitatively different microstructure: model Vycor glass represented by Gaussian porous media; model nanoparticle assemblies; and model open-cell solid foams created by colloidal templating. The relationship between the shape of the pore-size distribution and the morphological features of the porous medium is discussed, and the mean pore radius evaluated by the virtual capillary condensation method is compared with the equivalent hydraulic radius in each case. The two radii are shown to be correlated, but the correlation coefficient is different, and therefore characteristic, for each class of porous media.

Soil porosity and water infiltration as influenced by tillage methods

The relations between soil pore structure induced by tillage and infiltration play an important role in flow characteristics of water and solutes in soil. In this study, we assessed the effect of long-term use of various tillage systems on pore size distribution, areal porosity, stained (flow-active) porosity and infiltration of silt loam Eutric Fluvisol. Tillage treatments were: (1) ploughing to the depth of 20 cm (conventional tillage (CT)); (2) ploughing to 20 cm every 6 years and to 5 cm in the remaining years (S/CT); (3) harrowing to 5 cm each year (S); (4) sowing to the uncultivated soil (no tillage (NT)), all in a micro-plot experiment. Equivalent pore size distribution was derived from the water retention curve, areal porosity – from resin-impregnated blocks (8 cm × 9 cm × 4 cm) and stained porosity – from horizontal sections (every 2 cm) of column samples (diameter: 21.5 cm, height: 20 cm) taken after infiltration of methylene blue solution. The pore size distribution curves indicated that the textural peaks of the pore throat radius of approximately 1 μm were mostly defined under NT, whereas those in the structural domain of radii of 110 μm radius—under CT. The differences among the tillage treatments were more pronounced at depth 0–10 cm than 10–20 cm. At both depths, the differences in pore size distribution between the tillage treatments were relatively greater in structural than those in the matrix domain. CT soil had the greatest areal porosity and stained porosity. The stained porosity as a function of depth could be well described by logarithmic equations in all treatments. Cumulative infiltration (steady state) as measured by the double ring infiltrometer method was the highest under CT (94.5 cm) and it was reduced by 62, 36 and 61% in S/CT, S and NT soil, respectively. Irrespective of tillage method, cumulative infiltration rates throughout 3 h most closely correlated with stained porosity in top layers (0–6 cm). Overall, the results indicate that soil pore system under CT with higher contribution of large flow-active pores compared to reduced and no tillage treatments enhanced infiltration and water storage capacity.

Determination of an equivalent pore size from acoustic flow measurements

The hydraulic radius, rh, is defined as the ratio of a channel’s cross-sectional area to its perimeter. This parameter is important for specification of the performance of a porous medium that can be used as a regenerator in a Stirling engine or refrigerator. It is easy to calculate rh for pores of regular geometry, but difficult in more complex media. Two techniques which use oscillating flow to determine this parameter will be presented and compared. One technique extracts rh by finding the low velocity limit of the standard expression for viscous pressure drop in the Poiseuille flow regime. The other involves a plot of the nondimensional viscous flow resistance, Δpvis/Δxωρu, versus the reciprocal of the viscous penetration depth, 1/δν, in the laminar flow regime. When rh<δν, the flow behavior is frequency independent and the dynamics is characterized by rh only. When rh>δν, the flow resistance is frequency dependent and the dynamics is characterized by both rh and δν. It is possible to identify an effective hydraulic radius by equating it to the value of δν where that transition occurs. [Work supported by ONR.]

Observations on solvent flux and solute rejection across solvent resistant nanofiltration membranes

Organic solvent nanofiltration is an emerging technology made possible by the recent development of solvent resistant nanofiltration (SRNF) membranes. These membranes have many potential applications from continuous operation over many months in refinery systems [1,2] to short term operation for a few hours in batch chemical processes [3]. In this paper, solvent flux decline and membrane separation properties are investigated (including their dependence on pressure), using methanol with quaternary alkyl ammonium bromide salts with molecular weights (MW) in the range 322 to 547 Daltons as solutes. The membranes are characterised in terms of an equivalent uniform pore size using three simple pore flow models: Ferry model, Steric Hindrance Pore (SHP) model and Verniory model.