Effective Pore Radius Research Articles

Multi-scale multi-objective optimization and uncertainty analysis of methane-fed solid oxide fuel cells using Monte Carlo simulations

In this work, a multi-objective optimization approach is adopted for methane fueled solid oxide fuel cells in both microstructural and operational points of view. The optimization procedure was performed at different stages where microstructural parameters were considered separately and also in combination with operational variables in 2-objective and 3-objective cases. Effective reaction area, total conductivity and average pore radius are taken as the micro-model objective functions while system efficiency and power density as the multi-scale objectives are to be maximized. Electronic phase volume fraction, porosity, fuel utilization and steam/methane ratio are some of the important design parameters. The results of multi-objective problem are presented in terms of Pareto fronts of non-dominated solutions in which the compromised designs depicted among them. By multi-objective optimization of the microstructure of a solid oxide fuel cell anode, optimal electronic and ionic particle size of 0.4 and 0.26 μm, electronic volume fraction of 59% and porosity of 48% are determined. In addition, an optimum trade-off solution with 52% efficiency and 0.699 W/cm2 power density is achieved by multi-scale multi-objective optimization of the system. Finally, an uncertainty analysis is implemented based on Monte Carlo simulations to show the statistical performance of system outputs as well as the probability of failure of system constraints.

A model for non-Newtonian flow in porous media at different flow regimes

Polymeric liquids are of great practical importance for porous media flow as they can be used to improve the sweep of water in the reservoir and therefore improve the recovery of oil. Due to the non-Newtonian behavior of these liquids, they are extremely challenging to model. In this paper, we present a model that is capable of describing the most commonly observed flow regimes in porous media: (i) Newtonian, (ii) Shear thinning, (iii) Shear thickening, and (iv) Mechanical degradation. The novel feature of our model is that the time constants for the shear thinning and shear thickening behavior are related to variations in reservoir properties and conditions, thus making it possible to translate lab results to larger scale without introducing new fitting parameters. Furthermore, we present a way to estimate polymer mechanical degradation in porous media. In our model, the polymer degradation rate is linked to the effective pore radius (using a Kozeny-Carman type equation), shear stress, and polymer molecular weight, M w . The degradation results in a lower M w , while the polymer volumetric concentration is unaffected. The model is applied to a series of laboratory core flood experiments conducted with partially hydrolyzed polyacrylamide, HPAM, of different initial M w ranging from 5 to 20 MDa in seawater, and core permeability varied from 137 to 2019 mD. The flow rate is varied approximately three orders of magnitude and covers the shear thinning, shear thickening, and degradation flow regimes. We show that our model is able to reproduce experimental rate-dependent flow resistance, as well as viscosity of effluent samples. An important aspect supporting the use of the model as a predictive tool is that all the simulations with a given brine have made use of a single set of input parameters to describe the observed shear thickening and degradation behavior. Simulation of a second experimental series using low salinity brine required a separate set of input parameters for the shear thickening and shear degradation. The onset of shear thickening was not affected while shear thickening was reduced and degradation appeared to be slower.

Pore radius distribution and fractal dimension derived from spectral induced polarization

The pore size distribution provides a suitable description of the pore space geometry that can be used to investigate the fractal nature of a pore space or to determine the fractal dimension. The fractal dimension describes the size of the geometric objects as a function of resolution. It can be integrated into the models that are used for permeability prediction. We investigated the fractal dimension of the pore volume of 11 Eocene sandstone samples from China. This study describes an approach to use spectral induced polarisation spectra to estimate the pore size distribution and to determine the fractal dimension of the pore volume. Additionally, the fractal dimension was derived from data of the capillary pressure curves from mercury intrusion and the transversal relaxation time distribution of nuclear magnetic resonance. For samples with an effective pore radius larger than 1 μm, a good agreement exists between the values of the fractal dimension derived from the three different methods, which implies an identification of similar pore structures. Spectral induced polarisation can be a non-invasive laboratory technique for the estimation of the pore size distribution, but the application of the methodology to field measurements remains a challenging problem considering the limited frequency range.

Nanofiltration applied in gold mining effluent treatment: Evaluation of chemical cleaning and membrane stability

The objectives of this study were (1) to determine the best conditions of chemical cleaning of a nanofiltration (NF) membrane (NF90) employed in the treatment of gold mining effluent, and (2) to investigate the effects of continuous exposure to mining effluent and an acid cleaning agent on NF characteristics. NF fouling was mainly due to inorganic species, and calcium sulfate (CaSO4·0.5H2O) was identified over membrane surface. Therefore, acid solutions were the most efficient in membrane cleaning, and among them hydrochloric acid (HCl) showed the best performance. Cleaning without recirculation (soak) was not effective and thus 90-min recirculation was chosen as the best cleaning procedure. The NF membrane was exposed to the effluent and to the combined effluent and HCl solution for 285days. Modifications in hydrophobicity, effective pore radius, fouling, and surface charge were observed. The retention of magnesium sulfate and glucose by the membrane exposed to the combined effluent and cleaning solution was statistically lower, what endorses the importance of cleaning conditions optimization. No indication of degradation of the polymeric material of the membrane was observed. Thus, the results of this study are promising and demonstrate the robustness of NF technology for gold mining effluent treatment.

The effects of the different curing conditions and the role of added aggregate in the strength of repair mortars

Four ready-mix commercial available repair mortars—that are used for porous limestone repair—were studied under different laboratory conditions. To have better compatibility with porous limestone, not only pure mortars but also mortars with 50 wt% of limestone aggregate was tested. The reason why limestone aggregate was added to mortar was to modify the strength and porosity. Samples kept under climate control, dry and humid conditions were tested to understand the influence of environmental conditions. The bulk density and uniaxial compressive strength of cubic specimens were measured 3, 7, 14, 28 and 90 days after casting. The microscopic analyses revealed that tested repair mortars contain Portland cement and also non-hydrated cement particles even after curing. The strength of mortars in time does not show similar changes; however, specimens kept under dry conditions show the lowest strength 90 days after casting. High humidity leads to lower strength than normal humidity for tested mortars, but there is one mortar with added limestone aggregate, which has higher strength under humid conditions. In general, adding 50% of porous limestone aggregate reduced the strength and increased the density of repair mortars kept in climate chamber. Limestone aggregate that has larger pores causes a shift in effective pore radii toward smaller pores of 50% limestone aggregate mortar mixtures compared to pure mortars, with one exception. Tests results indicate that these commercially available repair mortars, even though they are suggested to be used for porous limestone, behave very differently under different environmental conditions and that adding limestone aggregate do not shift properties of the mortars toward appropriate compatibility.

Measurement of Heat Flow Transmitted through a Stacked-Screen Regenerator of Thermoacoustic Engine

A stacked-screen regenerator is a key component in a thermoacoustic Stirling engine. Therefore, the choice of suitable mesh screens is important in the engine design. To verify the applicability of four empirical equations used in the field of thermoacoustic engines and Stirling engines, this report describes the measurements of heat flow rates transmitted through the stacked screen regenerator inserted in an experimental setup filled with pressurized Argon gas having mean pressure of 0.45 MPa. Results show that the empirical equations reproduce the measured heat flow rates to a mutually similar degree, although their derivation processes differ. Additionally, results suggest that two effective pore radii would be necessary to account for the viscous and thermal behaviors of the gas oscillating in the stacked-screen regenerators.

Effect of post-polymerization anion-exchange on the rejection of uncharged aqueous solutes in nanoporous, ionic, lyotropic liquid crystal polymer membranes

The selectivity of a bicontinuous cubic, lyotropic liquid crystal (LLC) polymer nanofiltration membrane containing uniform cationic nanopores was manipulated via anion-exchange at the pore wall by soaking the fabricated membranes in aqueous salt solutions. Monovalent organosulfonate anions of various sizes were completely exchanged as the counterion at the pore walls to explore the impact of anion size on uncharged molecular solute rejection and water permeance. It was found that larger organosulfonate anions associated at the pore walls induced a higher rejection of uncharged solutes and a lower water permeance. The change in selectivity of the nanopores was described quantitatively through the calculation of the effective pore radius. The effective pore radius in these modified membranes was found to vary from 0.9±0.2 to 0.55±0.08nm depending on the resident organosulfonate counterion, demonstrating sub-1-nm resolution in pore size manipulation. An empirical model was used to demonstrate that physicochemical properties (molecular volume and hydrophobicity) of the resident counterion correlate with the observed solute rejection, suggesting that the counterion can be chosen to target a desired membrane performance. The ability to manipulate uniform, nm-sized pores with sub-1-nm resolution via simple anion-exchange offers a new avenue to tailor nanofiltration membrane performance.

DESIGN, MANUFACTURING, AND CHARACTERIZATION OF COPPER CAPILLARY STRUCTURES FOR LOOP HEAT PIPES

Mono and bi-layer capillary structures are designed by means of a thermo-hydraulic model of a loop heat pipe in order to optimize the performance of the system. The model tends to show that bi-layer wicks with a thermally conducting bottom layer and an insulating top layer are the most efficient in loop heat pipes. An experimental study is then led to manufacture and characterize the bottom layer. Eight samples made of copper powder are manufactured following a two-level fractional factorial design. The top layer is not manufactured in this study. The sintering parameters are adjusted to provide porous samples with sufficient mechanical resistance. The porous structure permeability and its capacity to provide a sufficient capillary pressure are evaluated using a specific test bench dedicated to this study, as well as with microstructural observations (tomography, microscopy). The experimental characterization of the samples enables to determine the influence of each sintering parameter as well as the interactions between them. The characteristics of the porous samples are found to be mainly affected by the sintering time and the pressure. High values of these parameters decrease the permeability and the porosity but increase the maximum capillary pressure due to a smaller effective pore radius. A set of optimum sintering parameters is found in order to manufacture the bottom layer. The best porous structure is supposed to enhance the latent heat transfer in a LHP.

Study of Nickel Wick Structure Applied to Loop Heat Pipe with Flat Evaporator

This study investigated the use of sintered Nickel powder as the wick material of Loop heat pipe with flat evaporator (Flat loop heat pipe, FLHP) and its effect on the heat transfer performance. Add the 1-heptanol into water and form Self-rewetting Fluid (SRF), resulting in the Marangoni effect. The colder liquid can be transport to the heating surface, delaying the occurrence of dry-out and increasing the critical heat load. This paper use Surface tension measurements to measure the change of 1-heptanol SRF, then it was apply to nickel wick FLHP as working fluid to investigate its effect on the heat transfer performance. This study successfully established production process of Nickel wick structure. Results of wick structure for the effective pore radius of 2.6 μm, porosity of 62%, permeability of 5.7 × 10-13m2. Results of Surface tension measurements show that 1-heptanol aqueous solution’s surface tension increases with increasing temperature, Results from applying 0.1% 1-heptanol aqueous solution to FLHP as working fluid. For performance testing show that the critical heat load was 240 W and the total thermal resistance was 0.77 ° C/W. Compared with FLHP with pure water, SRF raised the maximum heat flux of 70%, the total thermal resistance of the system reduces 40%, SRF has the potential to enhance the heat transfer performance of FLHP.

Passive permeability and effective pore size of HeLa cell nuclear membranes

Nuclear pore complexes in the nuclear membrane act as the sole gateway of transport of molecules from the cytoplasm to the nucleus and vice versa. Studies on biomolecular transport through nuclear membranes provide vital data on the nuclear pore complexes. In this work, we use fluorescein isothiocyanate-labeled dextran molecules as a model system and study the passive nuclear import of biomolecules through nuclear pore complexes in digitonin-permeabilized HeLa cells. Experiments are carried out under transient conditions in the time lapse imaging scheme using an in-house constructed confocal laser scanning microscope. Transport rates of dextran molecules having molecular weights of 4-70 kDa corresponding to Stokes radius of 1.4-6 nm are determined. Analyzing the permeability of the nuclear membrane for different sizes the effective pore radius of HeLa cell nuclear membrane is determined to be 5.3 nm, much larger than the value reported earlier using proteins as probe molecules. The range of values reported for the nuclear pore radius suggest that they may not be rigid structures and it is quite probable that the effective pore size of nuclear pore complexes is critically dependent on the probe molecules and on the environmental factors.

Poly(m-phenylene isophthalamide) (PMIA): A potential polymer for breaking through the selectivity-permeability trade-off for ultrafiltration membranes

The selectivity-permeability trade-off represents a limitation to the performance of ultrafiltration (UF) membranes. Theoretically, this trade-off is mainly determined by the pore structure, including the porosity, pore radius distribution and skin layer thickness. Benefiting from its high rigidity and high surface free energy, poly(m-phenylene isophthalamide) (PMIA) is proposed for preparing a high-performance UF membrane. In this work, PMIA membranes with various effective pore radii (6.58nm, 6.84nm and 9.28nm) were fabricated via nonsolvent-induced phase separation (NIPS). Through selectivity-permeability analysis, the PMIA membrane was found to break through the trade-off between selectivity and permeability. Compared with other UF membranes, the PMIA membrane exhibited a high porosity, narrow pore radius distribution and excellent hydrophilicity, leading to its high performance in the filtration process. This phenomenon could probably be attributed to the high rigidity, which confined the motion of the PMIA chain to suppressing pore collapse during pore formation, as well as to the high surface free energy that caused the hydrophilicity. All of these results clearly indicated that PMIA might be the most appropriate polymer for fabricating the UF membrane.

Effect of large gas-oil capillary pressure on production: A compositionally-extended black oil formulation

Pore sizes are typically on the order of nanometers for many shale and tight rock oil reservoirs. Such small pores can affect the phase behavior of in situ oil and gas owing to large capillary pressure. Current black-oil simulation practice is to alter the unconfined black-oil data for a fixed mean pore size to generate confined black-oil data with a suppressed bubble-point pressure. This approach ignores compositional effects on interfacial tension and the impact of pore-size distribution (PSD) with variable phase saturations on capillary pressure and phase behavior.In this paper, we develop a compositionally-extended black-oil model where we solve the compositional equations (gas, oil, and water components) directly so that black-oil data are a function of gas content in the oleic phase and gas-oil capillary pressure. The principle unknowns in the variable bubble-point fully-implicit formulation are oil pressure, overall gas composition, and water saturation. Flash calculations in the model are non-iterative and are based on K-values calculated explicitly from the black-oil data. The advantage of solving the black-oil model using the compositional equations is to increase robustness of the simulations owing to a variable bubble-point pressure that is a function of two parameters; gas content and capillary pressure. Leverett J-functions measured for the Bakken reservoir are used to establish the effective pore size-Pc-saturation relationship, where the effective pore size depends on gas saturation, which is the non-wetting phase saturation. The input fluid data to the simulator, e.g. interfacial tension (IFT), phase densities and viscosities, are pre-calculated as functions of pressure from the Peng-Robinson equation of state (PREOS) for three fixed pore sizes. During the simulation, at any pressure and saturation, fluid properties are calculated at the effective pore radius by using linear interpolation between these three data sets. We compare the results of the compositionally-extended black oil model with those of a fully-implicit eight-component compositional model that we have also developed. The results for the Bakken reservoir show that including PSD in the model can increase estimated recoveries by nearly 10% for initially undersaturated reservoirs while the increase can be over 100% for initially saturated reservoirs. Capillary pressure significantly increases the original oil-in-place (OOIP) for reservoirs that would otherwise be initially saturated leading to larger oil production.

Extrapolation of black- and volatile-oil fluid properties with application to immiscible/miscible gas injection

Black-oil fluid properties are determined by lab measurements or can be calculated through flash calculations of the reservoir fluid. Allowing for variable bubble-point pressures in black- or volatile-oil models requires a table of fluid properties be extended above the original bubble-point. Reservoir simulation accuracy, however, may be affected by discontinuities in the input data and poor predictions of extrapolated fluid properties. Common practice is to add surface gas to the original oil in the lab and increase the pressure to reach a new bubble-point. Another approach is to use linear extrapolation of oil and gas K-values with pressure on a log-log plot, where K-values are equal to 1.0 at a pseudo-critical or convergence pressure. The latter approach results in discontinuities in the phase behavior.We calculate continuous black-oil fluid properties above the original bubble-point by adding a fraction of the equilibrium gas at one bubble-point pressure to achieve a larger bubble-point pressure. This procedure continues until a critical point is reached at the top of the pseudocomponent pressure-composition diagram. Unlike other methods commonly used or recently proposed, the approach provides a smooth and continuous pressure-composition curve to the critical point. The model further allows for reinjection of produced gas, methane, or CO2 to increase oil recovery for both volatile and black oils. Further, the approach allows the use of black-oil or volatile-oil properties for tight rocks where capillary pressure alters the saturation pressures by decreasing the bubble-point pressure or increasing the dew-point pressure. Bubble-point pressure in the new model is a function of both capillary pressure (effective pore radius) and gas content. The phase behavior is illustrated using ternary diagrams for up to four components (water, oil, gas, and CO2 or CH4) and three phases (aqueous, oleic, gaseous) to allow for miscible and immiscible injection of various gases. The new phase behavior could be easily incorporated in a compositionally-extended black- or volatile-oil simulator. The approach could also be used to model gas condensate reservoirs with or without gas injection and capillary pressure. Finally, 1-D slim-tube simulations are made with the extrapolated black oil fluid properties to estimate minimum miscibility pressure (MMP) to demonstrate the applicability of the approach. Shocks occur in the 1-D displacement consistent with a compositional simulator.

Petrographic and petrophysical investigation on carbonate samples (Upper Cretaceous) from the Tushka Area (Egypt) with special focus on the effective pore radius

Petrographic and petrophysical properties of 42 carbonate rock samples from the Tushka Area, Egypt have been investigated. The samples originate from the Upper Cretaceous taken from seven shallow wells and were subdivided into three microfacies. The petrographic characterization of the glauconite-rich, fossiliferous limestones was carried out over 17 thin sections and an additional measurement of the glauconite content by color differentiation. The facies were characterized as (1) oolithic, low-dolomitic, and low-glauconitic, fossil-rich packstone with a tendency towards floatstone or rudstone; (2) glauconite-rich, low-dolomitic floatstone with a tendency towards rudstone; and (3) glauconite and iron mineral-rich, sparry calcitic cemented, and low-dolomitic rudstone. The petrophysical investigation providing grain density, porosity, electrical conductivity, specific internal surface, permeability, magnetic susceptibility, and the pore throat geometry supports the classification into three facies. A strong relation between permeability and formation factor is observed. The median pore radius derived from mercury porosimetry proves to be a good estimate of the effective hydraulic radius. An increased content of iron oxides was identified in facies 3. The increased iron content is related to higher values of both magnetic susceptibility and specific internal surface.

Effective pore size and radius of capture for K(+) ions in K-channels.

Reconciling protein functional data with crystal structure is arduous because rare conformations or crystallization artifacts occur. Here we present a tool to validate the dimensions of open pore structures of potassium-selective ion channels. We used freely available algorithms to calculate the molecular contour of the pore to determine the effective internal pore radius (rE) in several K-channel crystal structures. rE was operationally defined as the radius of the biggest sphere able to enter the pore from the cytosolic side. We obtained consistent rE estimates for MthK and Kv1.2/2.1 structures, with rE = 5.3–5.9 Å and rE = 4.5–5.2 Å, respectively. We compared these structural estimates with functional assessments of the internal mouth radii of capture (rC) for two electrophysiological counterparts, the large conductance calcium activated K-channel (rC = 2.2 Å) and the Shaker Kv-channel (rC = 0.8 Å), for MthK and Kv1.2/2.1 structures, respectively. Calculating the difference between rE and rC, produced consistent size radii of 3.1–3.7 Å and 3.6–4.4 Å for hydrated K+ ions. These hydrated K+ estimates harmonize with others obtained with diverse experimental and theoretical methods. Thus, these findings validate MthK and the Kv1.2/2.1 structures as templates for open BK and Kv-channels, respectively.

Influences of adsorption/desorption of shale gas on the apparent properties of matrix pores

The adsorption/desorption effects impact the petro-physical properties of matrix pores during gas depressurizing production, such as effective pore radius, effective porosity, apparent permeability, which will further impact the gas flow regime. In this paper, the dynamic models of effective pore radius and apparent permeability under the action of gas adsorption/desorption are derived. The mathematical model of shale gas flow is established considering the effects of adsorbed gas on apparent properties and gas flow regime. After that, the model is solved and validated using a finite volume method and experimental and field data. Finally, the variations of apparent parameters of matrix pores and gas flow regimes during gas production, and the influences of adsorption on gas production are demonstrated. The results show that the effective pore radius, porosity and apparent permeability increase during gas production; the gas flow regime in stimulated reservoir volume (SRV) changes from slip flow to transition flow; if the impacts of adsorbed gas on gas production is overlooked, both original gas in place (OGIP) and gas production will be significantly overestimated. The cumulative gas production changes slightly as the adsorption layer thickness increases, but the gas recovery factor decreases.

Modeling of Hydrophysical Properties of the Soil as Capillary-Porous Media and Improvement of Mualem-Van Genuchten Method as a Part of Foundation Arrangement Research

Within the concepts about the capillarity and the lognormal distribution of effective pore radii, a theoretical justification for function of differential water capacity and its antiderivative (function of water-retention capacity in form of a dependence of the soil volumetric water content on capillary pressure of the soil moisture) is presented. Using these functions, the ratio of soil hydraulic conductivity function to the filter coefficient is calculated. Approximations to functions describing the water-retention capacity and relative hydraulic conductivity of the soil have been suggested. Parameters of these functions have been interpreted and estimated with applying the physical and statistical indices of the soil.

Electron Percolation In Copper Infiltrated Carbon

Abstract The work describes the dependence of the electrical conductivity of carbon materials infiltrated with copper in a vacuum-pressure autoclave on copper concentration and on the effective pore radius of the carbon skeleton. In comparison with non-infiltrated material the electrical conductivity of copper infiltrated composite increased almost 500 times. If the composite contained less than 7.2 vol% of Cu, a linear dependence of the electrical conductivity upon cupper content was observed. If infiltrated carbon contained more than 7.2 vol% of Cu, the dependence was nonlinear – the curve could be described by a power formula (x − xc ) t . This is a typical formula describing the electron percolation process in regions containing higher Cu fraction than the critical one. The maximum measured electrical conductivity was 396 × 104 Ω−1 m−1 for copper concentration 27.6 vol%. Experiments and analysis of the electrical conductivity showed that electron percolation occurred in carbon materials infiltrated by copper when the copper volume exceeded the critical concentration. The analysis also showed a sharp increase of electrical conductivity in composites with copper concentration higher than the threshold, where the effective radius of carbon skeleton pores decreased to 350 nanometres.

Influence of gas transport mechanisms on the productivity of multi-stage fractured horizontal wells in shale gas reservoirs

In order to investigate the influence on shale gas well productivity caused by gas transport in nanometer-size pores, a mathematical model of multi-stage fractured horizontal wells in shale gas reservoirs is built, which considers the influence of viscous flow, Knudsen diffusion, surface diffusion, and adsorption layer thickness. A discrete-fracture model is used to simplify the fracture modeling, and a finite element method is applied to solve the model. The numerical simulation results indicate that with a decrease in the intrinsic matrix permeability, Knudsen diffusion and surface diffusion contributions to production become large and cannot be ignored. The existence of an adsorption layer on the nanopore surfaces reduces the effective pore radius and the effective porosity, resulting in low production from fractured horizontal wells. With a decrease in the pore radius, considering the adsorption layer, the production reduction rate increases. When the pore radius is less than 10 nm, because of the combined impacts of Knudsen diffusion, surface diffusion, and adsorption layers, the production of multi-stage fractured horizontal wells increases with a decrease in the pore pressure. When the pore pressure is lower than 30 MPa, the rate of production increase becomes larger with a decrease in pore pressure.

Micro-scale simulation of unidirectional capillary transport of wetting liquid through 3D fibrous porous media: Estimation of effective pore radii

The effective and representative pore radii (R50) determined from the physical experiments such as capillary penetration and porosimetry were found to be different for porous materials like ceramic and particulate structures. These differences were attributed to contact angle variations, possibly induced by contaminations. In this paper, we studied the relationship between effective and representative pore radii using “numerical experiments”, in which the contact angle variations were eliminated by using a constant contact angle. Micro-scale simulations of capillary penetration of a wetting liquid (air–water configuration) through virtual fibrous media were performed using a finite-volume-based volume-of-fluid (VOF) method. From the simulations, it was found that unidirectional liquid penetration followed Lucas–Washburn kinetics (L∼t) at the micro-scale, except during the initial stages that are dominated by the inertial forces. Even though the contact angle was held constant in the numerical simulations, the effective pore radii of the fibrous structures differed significantly from the representative pore radii (R50). The results suggest that a unique value for the characteristic pore radius does not exist for a porous medium, and the value of characteristic pore radius is strongly dependent on the experimental technique used to characterize the medium. Thus, the choice of experimental technique (e.g. porosimetry or capillary penetration experiment) to determine a characteristic pore radius should be based on the end application of the porous material.