Resistance Of Pores Research Articles

Modeling and simulation-assisted strategies for effective membrane-fouling mitigation during membrane bioreactor operation

This research principally aimed to present a suitable strategy for membrane-fouling mitigation in membrane-bioreactors (MBRs). The current strategies for membrane-fouling mitigation before initiating the process in many cases, are unmodifiable for a specific MBR system along the operations. Thus, membrane-fouling strategies during filtration should be applied. To select the best and most economical method for controlling fouling during the operations, the quality (site and mechanism) as well as quantity (thickness, mass, and porosity of the cake layer, and pore resistances) of fouling should be predicted. Accordingly, in this research, two powerful tools, i.e. modeling and simulation, have been used for predicting the quality and quantity of fouling, respectively. Through modeling, the best model describing the site and mechanism of fouling was chosen. Through simulation, the thickness, mass and porosity of the cake layer, along with resistance of cake and pores were calculated. In addition, the match between the results of modeling, simulation, and experimental results confirmed the accuracy of the performed predictions. Ultimately, to achieve the minimum membrane-fouling during filtration, based on the modeling results, the general solution of washing (physical or chemical), and based on the simulation results, its intensity (low, medium, and high) were proposed.

Rational Design of 3-Dimensional Carbon Architectures with Controlled Interfacial Activity for Reversible Li Metal Storage

Three-dimensional (3D) host architectures for Li metal storage have emerged as promising strategies for resolving the critical issues of Li metal anodes: severe volume changes and dendritic growth of Li during charge–discharge processes. However, the ionic resistance of electrolyte-filled pores causes the preferential deposition of Li on top of the 3D architecture (i.e., top plating), resulting in early cell failure. To realize Li metal anodes with high capacity and cyclability, herein, we report 3D-architectured electrodes with controlled interfacial activity based on metal–organic framework (MOF)-derived carbon hosts. Electrochemical simulations of Li plating processes in the 3D-architectured electrode suggest that the top plating can be effectively suppressed by increasing the interfacial activity across the thickness toward bottom of the electrode. MOF nanoparticles are pyrolyzed to form highly porous carbon hosts, and then, atomic Ag clusters are incorporated into the host by a galvanic displacement reaction to enhance the interfacial activity. A bi-layered carbon electrode with controlled interfacial activity is fabricated via sequential electrophoretic deposition of the host materials: i.e., as-pyrolyzed carbon on top and Ag-incorporated carbon on bottom. In comparison with the conventional electrode with uniform interfacial activity, the bi-layered electrode exhibits reduced overpotentials for Li plating and enhanced cyclability during galvanostatic Li plating–stripping. The combined computational and experimental studies further demonstrate that the bottom layer with atomic Ag clusters acts as a preferential site for Li nucleation even in the presence of kinetic limitations of ionic transport. As a result, Li deposits are confined in the bi-layered carbon electrode, thereby enhancing the reversibility of Li metal storage. This work provides an effective strategy to develop long-cycling, high-capacity Li metal anodes by controlling the interfacial activity of 3D carbon architectures.

A potential online quantifier of sludge dewaterability developed from the similitude of water and electricity: Understanding the water release resistances as the medium

Chemical conditioning is a common but chemicals consuming procedure for improving sludge dewatering performance. However, real-time monitoring of dewaterability for accurate regulation of conditioner dosage is still tricky. One of the pending questions causing this challenge is that the key mechanisms affecting water release are not fully revealed. This study traced the entire process of water release in sludge flocs to investigate and clarify the possible release resistances, including the viscous resistance derived from binding effect of contact interface, and the interfacial resistance originating from morphology of pore wall, as well as the resistance arising from structure of flocs. Key resistances in an individual nanopore were determined using the state-of-art principles in confined water flow. Then the investigation was expanded to the multi-porous flocs scale. Based on the water release behavior and inspired by the similitude of water and electricity, an online quantifier derived from electrical impedance spectroscopy (EIS) analysis was developed to achieve real-time determination of dewaterability in a probe-like type. Our results showed that both viscous resistance of pores and structural resistance of flocs affected the water release, the contribution of flocs structural resistance cannot be neglected. Moreover, strong linear correlations (r ≥ 0.943, p < 0.01) were obtained between the online quantifier, named normalized spectral dimension, and the sludge dewaterability in two typical sludge conditioning processes. The optimal dosages were successfully revealed by normalized spectral dimension in an established semi-automatic conditioning and online dewaterability monitoring system. These observations may promote the development of smart sludge treatment technologies.

Effects of electroflocculation/oxidation pretreatment on the fouling characteristics of ultrafiltration membranes.

In order to reduce the membrane pollution of ultrafiltration caused by natural organic matter and improve the treatment efficiency, electroflocculation/oxidation is used as the premembrane treatment method. The membrane specific flux attenuation characteristics was compared and analyzed under the conditions of direct ultrafiltration and electroflocculation/oxidation-ultrafiltration. Combined with the analysis of the reversibility of membrane fouling, the mechanism of electroflocculation/oxidation pretreatment to alleviate ultrafiltration membrane fouling was evaluated, and the membrane pore clogging model was used to fit the fouling law. The results show that, in the continuously fed filtration experiment, the electroflocculation/oxidation process involved in the pretreatment and the direct ultrafiltration membrane filtration decreased the ultrafiltration membrane flux to 79.1% and 28.5%, respectively. The reversible resistance generated by ultrafiltration and electroflocculation/oxidation-ultrafiltration processes accounted for 37.70% and 62.26% of their total pollution resistance, whereas the irreversible resistance generated accounted for 47.30% and 12.40%, respectively. Meanwhile, the direct correlation between the the flux dropped and complete clogging became less than that of the ultrafiltration process. The pretreatment significantly strengthened irreversible fouling resistance of the membrane pores. The membrane permeation flux was significantly increased after the electroflocculation/oxidation pretreatment.

Liquid phase blockage in micro-nano capillary pores of tight condensate reservoirs

The development of tight condensate gas reservoirs faces complex formation damage mechanisms, seepage characteristics and hydrocarbon phase changes, which are common challenges for both tight gas reservoirs and condensate gas reservoirs. In the near-well area, the liquid phase blockage problem due to water phase retention formed by capillary spontaneous imbibition of invasive water and oil phase accumulation due to retrograde condensation precipitation has become a key obstacle to the efficient development of tight condensate gas reservoirs. Experiments were conducted to evaluate the damage of liquid phase blockage under different conditions near the wellbore area. The results show that when the liquid phase saturation in the near-wellbore area increased to 80.12%, the relative permeability of the gas phase decreased to 0. It is concluded that the mixed wettability of formation rocks, ultra-low water saturation, abundant hydrophilic clay minerals and high capillary resistance of micro-nano pores are the main causes for the easy adsorption and retention of liquid phase. Reduced pressure transmission capacity and irreversible formation damage induced by liquid-phase blockage are the two major controlling factors for the low liquid phase flowback rate. It is suggested that developing a flowback system based on the formation physical properties differentiation to control water phase invasion, and changing wettability or injecting thermochemical fluid to control condensate blocking are feasible methods to relieve liquid phase blockage damage in tight condensate reservoirs. Cited as: Wang, Y., Kang, Y., Wang, D., You, L., Chen, M., Yan, X. Liquid phase blockage in micro-nano capillary pores of tight condensate reservoirs. Capillarity, 2022, 5(1): 12-22. https://doi.org/10.46690/capi.2022.01.02

Thermal resistance and thermal rectification of silicon device with triangular pores: A molecular dynamics study

The thermal rectification has potential applications in the thermal management and thermal signal processing. By using the nonequilibrium molecular dynamics method, the thermal resistance of triangular pores in the silicon device is analyzed. The evident thermal rectification phenomenon has been detected in silicon device with triangular pores. It is found that the thermal rectification can be tuned through the angles and the distribution of pores. A moderate angle and pattered arrangement of triangular pores are preferable to achieve a higher thermal rectification ratio. The simulated thermal resistance caused by pores is on the order of 10−10m2K/W and the thermal rectification ratio can be up to 29.6%. Moreover, by designing the distributions of groups of triangular pores, the obtained thermal rectification ratio ranged from 10.0% to 27.5%. This work indicates that the silicon structures with pores are promising to be made into the thermal rectifier.

(Invited) Bottom-up Growth of Lithium in Three–Dimensional Porous Framework Electrodes

The Li metal anode has attracted much attention, because of its high specific capacity and low electrochemical potential. However, its commercial viability is hindered by the uncontrollable growth of Li dendrites as well as large volume changes over battery cycling. Li storage in three-dimensional (3D) porous framework electrodes of metals and carbon is believed to be effective for resolving those problems with 2D Li metal. However, 3D framework electrodes still suffer from uneven Li plating–stripping: during Li plating, Li preferentially nucleates and grows on top of the framework electrode (facing the separator) because the ionic resistance of electrolyte-filled pores inhibits the migration of Li+ deep into the electrode bottom (facing the current collector). The so-called “top growth” becomes severe in the presence of any protrusions or roughness on the top surface due to the concentrated Li+ flux. In contrast to the general expectations, therefore, the 3D framework electrodes tend to exhibit poor cycling stability and early cell failure. Herein, we present a combined modeling and experimental study showing the manipulation of the Li plating behavior in the 3D framework electrode via interfacial activity tuning. Based on the understanding of the multiple reaction kinetics in the porous framework electrode, we propose an interfacial activity gradient (IAG) design as an effective approach to enable the “bottom-up growth” of Li even without rigorous optimization of porous structures. The Li plating behaviors are theoretically studied on a “model” architecture via transmission line modeling and are experimentally proved. The theoretical and experimental results are in accord with each other, indicating that the IAG design enables the bottom-up growth of Li within the 3D framework electrode, while suppressing the top growth. The IAG electrode exhibits the outstanding improvement in morphological stability and electrochemical reversibility as compared with the conventional framework electrode with uniform interfacial activity.

AC impedance spectroscopy characteristics of chloride-exposed cement pastes

In this paper, the characteristics of AC impedance spectroscopy of cement paste immersed in chloride solution were measured and analyzed with a proposed equivalent circuit model. The elements in the proposed equivalent circuit, including the resistance of interface between electrode and specimens, resistance of continuous and discontinuous pore, capacitance of solid phase and electrical double layer (EDL) were discussed. The results showed that the resistance of interface between electrode and testing specimen was much lower than that of cement paste. With the increase of chloride concentration in the soaking solution, the resistance of continuous gradually decreased due to the higher conductivity of chloride solution. Stripped out the impacts of concentration of pore solution on resistance of pores, the resistance of continuous pore increased firstly due to the decrease of continuous pore volume from the formation of Friedel’s salt. However, the resistance of discontinuous pores gradually decreased with the increase of soaking solution concentration due to the transformation of continuous pores to discontinuous pores. The reaction between chloride ions and hydration products and formation of Friedel’s salt decreased the porosity of cement pastes and led to higher capacitance of solid phase. Based on an idealized two-plate capacitor model for EDL, the thickness of EDL was calculated from the measured capacitance. The decrease of EDL thickness with chloride concentration in soaking solution was in agreement with the results of chloride contents in EDL obtained from pore solution expression test.

Numerical Simulation of Small Defects Flow Resistance Characteristics of Thin-walled Components of Titanium Alloy with Adding Material Manufacturing Based on CT Data

In order to study the influence of different types of small defects on the flow resistance characteristics of thin-walled components, the method of micro-focus industrial CT images and numerical simulation was used. According to CT imaging technology, there were mainly three types of small defects on the inner surface of the runner: surface pores, surface inclusions, and surface cracks. Extracting small defects, refining the local grid, and establishing the finite element analysis model. Through finite element calculation software Fluent, a low Reynolds number k-e model was adopted to carry out numerical simulation and analysis on the flow channels with three small defects on the inner surface. The results showed that under the same Reynolds number condition, the flow resistance coefficient of surface cracks was the largest, which was much larger than that of surface inclusions and surface pores. The resistance of surface pores and surface inclusions to the flow passage was similar and relatively small. The flow resistance coefficient of three kinds of minor defects decreased with the increase of Reynolds number. In the case of low Reynolds number, the separation of flow boundary layer occurred at the surface cracks.

Impedance analysis of porous carbon electrodes to predict rate capability of electric double-layer capacitors

Electrochemical impedance analysis is performed to predict the rate capability of two commercial activated carbon electrodes (RP20 and MSP20) for electric double-layer capacitor. To this end, ac impedance data are fitted with an equivalent circuit that comprises ohmic resistance and impedance of intra-particle pores. To characterize the latter, ionic accessibility into intra-particle pores is profiled by using the fitted impedance parameters, and the profiles are transformed into utilizable capacitance plots as a function of charge–discharge rate. The rate capability that is predicted from the impedance analysis is well-matched with that observed from a charge–discharge rate test. It is found that rate capability is determined by ionic accessibility as well as ohmic voltage drop. A lower value in ionic accessibility for MSP20 is attributed to smaller pore diameter, longer length, and higher degree of complexity in pore structure.

The Role of Pore Geometry in Single Nanoparticle Detection

We observe single nanoparticle translocation events via resistive pulse sensing using silicon nitride pores described by a range of lengths and diameters. Pores are prepared by focused ion beam milling in 50 nm-, 100 nm-, and 500 nm-thick silicon nitride membranes with diameters fabricated to accommodate spherical silica nanoparticles with sizes chosen to mimic that of virus particles. In this manner, we are able to characterize the role of pore geometry in three key components of the detection scheme, namely, event magnitude, event duration, and event frequency. We find that the electric field created by the applied voltage and the pore's geometry is a critical factor. We develop approximations to describe this field, which are verified with computer simulations, and interactions between particles and this field. In so doing, we formulate what we believe to be the first approximation for the magnitude of ionic current blockage that explicitly addresses the invariance of access resistance of solid-state pores during particle translocation. These approximations also provide a suitable foundation for estimating the zeta potential of the particles and/or pore surface when studied in conjunction with event durations. We also verify that translocation achieved by electro-osmostic transport is an effective means of slowing translocation velocities of highly charged particles without compromising particle capture rate as compared to more traditional approaches based on electrophoretic transport.

Micro/nanoporous membrane based gas–water separation in microchannel

In this paper, a method coupling micro/nanoporous membranes with microchannels for the gas/water separation in microscale has been demonstrated. The principle of separation is based on the basic properties of membranes—wetted micro/nanoporous hydrophilic membranes can block gas due to a large water surface tension in the entrance of micro/nano pores to withstand the gas pressure, while it allows water to permeate with overcoming the flow resistance of pores; in contrast, hydrophobic membranes permit gas to penetrate but prevent water flow. These two kinds of membranes coupled with microchannels in cross-flow mode or dead-end mode can separate gas/water in microscale. The separation in cross-flow mode can achieve relative high water permeate flow rate, while the separation in dead-end mode can completely separate gas/water segments in a single operation step. The membrane-based separation method has low cost, easy integration into microfludics channels, design flexibility with two configuration modes (cross-flow and dead-end).

Parametric Studies on the Processing Parameters of a Thermally Wicking Material using Image Analysis

AbstractA heat pipe is a device that transports heat against gravity using a wicking material and evaporation-condensation cycle..In these systems a thermal wick moves fluid from the cool region of a heat pipe to the hot region, where evaporative cooling occurs. Due to the operating demands of a thermal wick, several microstructural features are integral to the performance of the wick: capillary radii, specific surface area and permeability. Measuring these properties of a thermal wick (capillary radii, specific surface area and permeability) is difficult, therefore image analysis methods of quantification of the critical properties of a thermal wick has been developed . However, the microstructure of a thermal wick contains semicontinuous pores, therefore connectivity of pores cannot be assumed during quantification of the critical properties.. Two processing parameters, sacrificial template particle size and sintering temperature, were varied during the thermal wick synthesis. Quantification of the critical properties of the thermal wick was performed using the newly developed method. The newly developed method was able to detect the an increase in the pore connectivity as the sintering temperature decreased, and an increase in the connectivity as the sacrificial template particle size decreased. The newly developed method was also able to describe the size distribution of individual pores as well as the hydraulic resistance and orientation of individual pores as well as estimate the porosity and true specific surface area of the different samples.

A study of mass transfer resistance in membrane gas–liquid contacting processes

The change of mass transfer resistance with time has been examined for membrane-based carbon dioxide absorption in water. A commercial polypropylene hollow fiber membrane module was used with gas flow through the lumen side and liquid cross-flow on the shell side. Experiments were carried out for a prolonged period of time to evaluate absorption performance. Absorption flux decreased significantly with time due to a developing resistance to mass transfer. However, the initial flux value was restored after membrane drying, indicating that the additional resistance was reversible. A theoretical model was developed to analyze and predict flux deterioration with time in terms of partial resistances in series. The resistance against pure gas mass transfer was considered to be the sum of the liquid phase resistance and the resistance of the membrane; the latter arises from membrane pore filling by gas or liquid or both. A shell side mass transfer correlation was used for the prediction of the liquid phase resistance. The experimental absorption flux decline with time was attributed to gradual partial pore filling by liquid, and it was used to estimate the magnitude of the membrane resistance and its temporal variation. Model predictions, in good agreement with experimental results, permitted the estimation of liquid penetration into the membrane matrix. Although this was relatively low (∼13%), the resulting resistance of the liquid-filled pores accounted for over 98% of the membrane resistance and for 20–50% of the total resistance to absorption.

Preparation of microporous membranes by TEOS/O 3 CVD in the opposing reactants geometry

The pore size of porous Vycor glass with a pore diameter of 4 nm was controlled by TEOS/O 3 CVD in the opposing reactant geometry. TEOS vapor and O 3 were fed with O 2 carrier through the bore and the outside of the tubes respectively. The influence of the TEOS and O 3 concentrations in the feed, as well as the temperature and period of the CVD reaction were analyzed in terms of gas transport properties of the resulting membranes. The control of reaction parameters enabled us to synthesize molecular sieve membranes with He/N 2 perm-selectivity values as high as 950 at 40°C. Gas molecules such as O 2 and N 2 exhibited activated diffusion through the membranes, though their permeability values were insignificantly low compared with the permeability of He molecules. The permeability of He molecules was found to be limited by the resistance of the support Vycor glass pores.

Evaluation of the anticorrosive behaviour of organic coatings applied on galvanised steel surfaces

The study of the anticorrosive behaviour of the four systems of organic coatings — two with coal tar epoxy layer and two with zinc rich epoxy layer and external coating with epoxy paint — which were applied to galvanised steel specimens and were exposed to NaCl solution leads to the following conclusions: ▀ All four systems investigated provide higher protection than simple galvanising during the exposure time of the present work, exhibiting corrosion current densities lower than those of the uncoated galvanised steel even after 4 months of exposure. ▀ The systems comprising coal tar epoxy demonstrate higher anticorrosive protection than the systems with zinc rich epoxy and external coating with epoxy paint. The former maintain lower corrosion curent densities, almost constant phase angle (80°–85°) in the whole frequency range of the measurements, and high values of coating resistance, resistance of pores, and exponent of the CPE of the bulk of the coating. These elements indicate a homogeneous and resistant system with no considerable change of its electrical characteristics which retains its capacitive behaviour, a fact which is also verified by the slight increase in the water uptake(%v) and by the visual observations. On the contrary, the latter demonstrate higher corrosion curent densities, a step-by-step decrease of the phase angle, a significant reduction of the coating resistance, the resistance of pores and the exponent of CPE, and the increase in the constant of CPE, clues which characterize non-homogeneous materials where an increased penetration of polar water molecules occurs. This is also confirmed by the tendency for an increased water uptake, the high values of dielectric losses and the appearance of conductive pathways. ▀ Independent of the coating system, the existence of a wash primer layer leads to an increase of the anticorrosive protection.

Spectroscopic and electrochemical studies of charge transfer in modified electrodes

Experimental results from electrochemical e.s.r. on electrodes modified with conducting polymers such as polyaniline, polypyrrole and polythiophene are presented. The results show that the polymer exists in two forms, one stable when it is insulating (α) and the other (β) when it is conducting. In the conducting region the kinetics of the transformation of the metastable α form into the β form can be followed by e.s.r. It is further shown that in the lightly oxidised films there is a one-to-one correlation between charge injected and e.s.r. spins. These results are explained by a chemical redox model as opposed to a delocalised band.Results from a.c. impedance studies are presented. These results are explained by an equivalent circuit which includes a novel transmission line with differential resistances. Theoretical impedance plots are derived. Experimental results show that the polymer resistance and the resistance of the aqueous pores are equal. Reasons for this finding are discussed.

Diffusive resistance of avian eggshell pores

Resistance to gas diffusion through the avian eggshell resides in the microscopic pores which penetrate the shell. We calculated the resistance to water vapor diffusion of individual pores in the shells of 23 species of avian eggs, based on measurements of pore dimensions taken from drawings of 321 pore casts published by Tyler (1962, 1964, 1965) and Tyler and Simkiss (1959). Diffusive resistances were calculated from Fick's first law, using a 100-segment of each pore. In addition, we added 2 series resistances, calculated from Stefan's law, to account for boundary layer resistances at the inner and outer pore apertures. Convective resistances for the same 100-segment model were compared from Poiseuille's law. A special, symmetrically branching model is presented for the diffusive resistance of the branched pores of ostrich eggshells, based on the drawings of Tyler and Simkiss (1959). The total aperture resistance was less than 6.2% of total pore resistance, while the outside aperture effect was on average only 1.5%. The calculated average pore conductance for all species was 5.4 μg (day Torr) −1, about three times higher than the average value of 1.6 μg (day Torr) −1 obtained by dividing measured shell conductance by the numbers of pores (Ar and Rahn, 1985). A possible explanation for this discrepancy is advanced. However, it is to be noted that in spite of the discrepancy, both calculated and functional values of pore conductance appear to be independent of egg mass.

Frost resistance and pore size distribution in bricks

Correlation between frost resistance, porosity and pore size distribution was examined. Different test methods were used to evaluate the frost resistance. Porosity and pore size distribution were examined in mercury intrusion porosimeter (MIP). Scanning electron microscopy gave a visual view of the pore geometry, pore size and porosity. A linear correlation was found between frost resistance and the inverse value of the intruded pore volume. A linear correlation was also found between frost resistance and percentage of pores with diameter bigger than 3 μm. The test results were analysed using statistical methods. From the MIP-test a frost resistance number can be calculated which indicates the frost resistance of the brick.

A comparison of photosynthesis in two thalloid liverworts.

Standard infra-red gas analysis techniques were used to compare the photosynthesis of the liverworts Marchantia foliacea Mitt. and Monoclea forsteri Hook. Parameters measured include net photosynthetic rates, light response curves, quantum efficiencies, diffusive resistances to CO2 and water, apparent photorespiration and chlorophyll content. A series of morphological measurements were also made to determine resistance of pores and the 'mesophyll' to dorsal surface ratio, A mes/A. Marchantia has a cuticularised thallus with the photosynthetic tissues arranged in air chambers giving an A mes/A of 9 whilst Monoclea has a solid thallus, A mes/A of 1. Both species are shade adapted and it was found that whilst the air chambers were advantageous for water relations they increased maximum photosynthesis only slightly. Calculations showed that the solid thallus would be photosynthetically superior in very moist environments. The results are discussed with reference to existing ideas on the evolution of the structure of land plants.