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A wide range of applications are possible with paper-based analytical devices, which are low priced, easy to fabricate and operate, and require no specialized equipment. Paper-based microfluidics offers the design of miniaturized POC devices to be applied in the health, environment, food, and energy sector employing the ASSURED (Affordable, Sensitive, Specific, User-friendly, Rapid and Robust, Equipment free and Deliverable to end users) principle of WHO. Therefore, this field is growing very rapidly and ample research is being done. This review focuses on fabrication and detection techniques reported to date. Additionally, this review emphasises on the application of this technology in the area of medical diagnosis, energy generation, environmental monitoring, and food quality control. This review also presents the theoretical analysis of fluid flow in porous media for the efficient handling and control of fluids. The limitations of PAD have also been discussed with an emphasis to concern on the transformation of such devices from laboratory to the consumer. [ABSTRACT FROM AUTHOR]

The paper proposes a new approach to gradient porous composites based on the Ti3Al(Si)C2 MAX phase. This approach is based on the production of preceramic paper with the different content of the powder filler based on MAX phases and their spark plasma sintering. The analysis of the microstructure and phase composition is conducted for these composites. It is shown that the obtained composites have a clear interface between layers with different porosity. It is found that the content of organic components in preceramic paper affects the phase composition of the fabricated composites. The MAX phase content in dense and porous layers is 86 and 56 vol.%, respectively. Microhardness measurements performed in the composite cross-section show the hardness of 600 to 800 HV, depending on the layer porosity and phase composition. [ABSTRACT FROM AUTHOR]

Paper is a material made from renewable resources, and it has been used intensively for almost 2000 years. It is a highly porous, bendable, and foldable flat structure of randomly arranged and connected fiber-like basic building blocks. The capability to transport fluids without pumps and sophisticated dosing systems is attractive. Paper microfluidics especially has gained increasing interest, particularly in the last decade. Although a number of interesting demonstration devices for easy-to-use diagnostic systems have been reported, only a limited number of these have found applications. This is mainly due to the geometric and chemical complexity of the material. While chemical functionalization (e.g., for defining hydrophobic barriers for spatially resolved fluid transport) is well advanced, understanding and controlling capillary-driven transport of a fluid within the complex porous matrix of paper. This article highlights recent advances and outlines design strategies for successful microfluidic paper-based applications. [ABSTRACT FROM AUTHOR]

Coated paper is an example of a multi-layer porous medium, involving a coating layer along the two surfaces of the paper and a fibrous layer in the interior of the paper. The interface between these two media needs to be characterized in order to develop relevant modeling tools. After careful cutting of the paper, a cross section was imaged using focused ion beam scanning electron microscopy. The resulting image was analyzed to characterize the coating layer and its transition to the fibrous layer. Such image analysis showed that the coating layer thickness is highly variable, with a significant fraction of it being thinner than a minimum thickness required to keep ink from invading into the fibrous layer. The overall structure of the coating and fibrous layers observed in this analysis provide insights into how the system should be modeled, with the resulting conclusion pointing to a specific kind of multi-scale modeling approach. [ABSTRACT FROM AUTHOR]

Constructing low-cost, high-catalytic-performance anode electrocatalysts is a significant challenge for methanol oxidation (MOR) and urea oxidation (UOR) reactions. Using paper templates with abundant pores to prepare thin porous metal materials helps to obtain high-performance electrode materials. The nano amorphous B-doped Ni/crystalline Ni (nanoam Ni-B/Ni) foil composite electrodes were derived from paper templates prepared by impregnation, high-temperature reduction, and electrodeposition methods. Porous Ni foils (Nip) derived thinnest rice ("Xuan") paper, initially used for Chinese calligraphy and painting, exhibits the best performance due to its strong adsorption and wettability. Compared to direct current electrodeposition, pulse electrodeposition yields finer amorphous B-doped Ni nanoparticles with good catalytic performance. Under a current density of 100 mA·cm−2, the nanoam Ni-B/Ni composite electrode prepared under a duty cycle of 0.5–1.0 s achieved current densities of 290.4 mA·cm−2 (MOR) and 340.4 mA·cm−2 (UOR) at 0.8 V, which are improved by 37.1% and 55.1%, respectively, compared to those of Nip. After 2000 cycles, with solution replacement, the current densities maintained 99.2% (MOR) and 81.6% (UOR) of the original values, showing excellent electrocatalytic stability. This research provided a new use for Chinese rice paper, and the prepared Nip-based electrode, with a thickness of about 60 μm and a low area quality, had a simple preparation process and good electrochemical properties, and can be used as a potential substitute for commercial Ni foam for portable or small electrochemical devices. [ABSTRACT FROM AUTHOR]

Improving the performance of porous nickel-based material used widely in the energy field is necessary. Alloying and increasing the specific surface area are essential approaches. This study used rice paper (Chinese traditional calligraphy and painting paper) as biomass templates to prepare hierarchical porous Ni and Ni-Cu foils (Nip and NiCup) with a thickness of about 60 μm by impregnating and high-temperature reduction process. The Ni3S2/Nip electrodes were prepared by an in situ-grown Ni3S2 nanosheet array on the struts of Nip via a hydrothermal process. Two modification methods using Cu-added alloying and Ni-S nanosheet growing were compared to determine their effects on the microstructure, phase, and performance in methanol oxidation (MOR) and urea oxidation (UOR). The results showed that both alloying effects and morphology control can promote MOR and UOR. Compared to the current density value of Nip at 0.8 V, the values of the preferred Ni10Cup and nanosheet array Ni3S2/Nip increased by 24.5% and 27.3% for methanol oxidation and by 15.4% and 38.4% for urea oxidation, respectively. Adding Cu helped to improve electron transfer and facilitated the transition from Ni2+ to Ni3+. The large specific surface area of Ni3S2 nanosheets provided more active sites for the reaction. Compared to Ni10Cup, Ni3S2/Nip with a lower impedance value exhibits better electrocatalytic performance and stability, achieving peak current densities of 269.7 mA cm−2 (MOR) and 303.9 mA cm−2 (UOR) at 0.8 V, maintaining 91.2% (MOR) and 102.4% (UOR) of the initial peak current density after 2000 cycles. The foil electrodes obtained under both modification strategies can be used as anode material in portable cells, and might also be applied to the oxidation of other small organic molecules. [ABSTRACT FROM AUTHOR]

Transport of volatile organic compounds (VOCs) through porous media with active surfaces takes place in many important applications, such as in cellulose-based materials for packaging. Generally, it is a complex process that combines diffusion with sorption at any time. To date, the data needed to use and validate the mathematical models proposed in literature to describe the mentioned processes are scarce and have not been systematically compiled. As an extension of the model of Ramarao et al. (Dry Technol 21(10):2007–2056, 2003) for the water vapor transport through paper, we propose to describe the transport of VOCs by a nonlinear Fisher–Kolmogorov–Petrovsky–Piskunov equation coupled to a partial differential equation (PDE) for the sorption process. The proposed PDE system contains specific material parameters such as diffusion coefficients and adsorption rates as multiplication factors. Although these parameters are essential for solving the PDEs at a given time scale, not all of the required parameters can be directly deduced from experiments, particularly diffusion coefficients and sorption constants. Therefore, we propose to use experimental concentration data, obtained for the migration of dimethyl sulfoxide (DMSO) through a stack of paper sheets, to infer the sorption constant. These concentrations are considered as the outcome of a model prediction and are inserted into an inverse boundary problem. We employ Physics-Informed Neural Networks (PINNs) to find the underlying sorption constant of DMSO on paper from this inverse problem. We illustrate how to practically combine PINN-based calculations with experimental data to obtain trustworthy transport-related material parameters. Finally we verify the obtained parameter by solving the forward migration problem via PINNs and finite element methods on the relevant time scale and show the satisfactory correspondence between the simulation and experimental results. Article Highlights: A mathematical model to describe transport of polar volatile organics through paper is proposed. Based on experimental data, the deep learning method of physics-informed neural networks (PINNs) is used to solve the inverse problem of finding the sorption time constant. Solutions for the forward problem are obtained by the standard finite element method (FEM) and PINN methods. These solutions are compared with each other as well as with the experimental data to verify the model. [ABSTRACT FROM AUTHOR]

During the extrusion coating of paper or paperboard, a molten film of polymer is pressed against a paper surface to generate waterproof packaging materials. Hot-melt glues are also applied to various porous materials and paperboard to generate packaging. In both cases, the penetration of the polymer into the pore space influences the product performance and the ability of the product to be recycled at the end of life. While there is much experimental work discussing various parameters in these operations, little theoretical work has been reported. Here, a simple model based on Darcy's law is proposed to predict the penetration of polyethylene (PE) into paper and paper that has been coated with cellulose nanofibers (CNF). Another model, based on the flow of a polymer into a pore that includes dynamic heat transfer is developed, where the viscosity is a function of temperature. Experiments were conducted where a PE film is pressed against samples and the amount of fiber recovery is characterized. The model predictions are compared to experimental results. Good agreement for different paper types, pressing times, and temperatures is obtained after a calibration factor is used. [ABSTRACT FROM AUTHOR]

The gas flow through sheet-like porous materials such as paper can show marked lateral variations due to a heterogeneous, locally varying microstructure. Hence, reliable predictions of such lateral flux variations require an appropriate consideration of local variations in the microstructure. The flow through such sheet-like materials is commonly described with Darcy's law in which permeances are formulated in terms of microstructure properties, such as porosities, tortuosities, or hydraulic radii. This work proposes an extension of existing permeance models that directly considers the variation and the cross-dependence between local microstructure properties. The extended model is applied to local air fluxes through a paper sheet to exemplarily reveal the joint impact of local porosities and local tortuosities on the air flux. The key extension is to consider a joint distribution of porosity and tortuosity. The latter is constructed from the univariate property distributions using a copula approach and yields local tortuosities including their variation for any encountered local porosity. These values jointly enter any permeance model that qualitatively captures the dependence of the air flux on the porosity. To assess the merit of the model, variations in the air flux and in the pore space properties are independently determined from the same measured microstructure of paper. Air flux variations are provided by computational fluid dynamics simulations on multiple, nonoverlapping segments taken from the microstructure. A statistical analysis of the entire microstructure provides the distribution of local porosity, tortuosity, and thicknesses. Our model quantitatively explains that porosity-dependent variations in the tortuosity, in particular the ones associated with high-volume pathways, decisively determine air flux variations. Article Highlights: Computational fluid dynamics simulations determine local variation of air flow through an actual microstructure of paper. Construction and use of the copula approach to model joint distribution of local porosities and tortuosities is explained. Existing permeance models equipped with variations in porosity and porosity dependent tortuosity capture most variations in air flow. [ABSTRACT FROM AUTHOR]

Paper-based friction materials are porous materials that exhibit anisotropy; they exhibit random pore sizes and quantities during their preparation, thereby rendering the control of their pore structure difficult. Composites with different pore structures are obtained by introducing chemical foaming technology during their preparation to regulate their pore structure and investigate the effect of pore structure on the properties of paper-based friction materials. The results indicate that the skeleton density, total pore area, average pore diameter, and porosity of the materials increase after chemical foaming treatment, showing a more open pore structure. The addition of an organic chemical foaming agent improves the curing degree of the matrix significantly. Consequently, the thermal stability of the materials improves significantly, and the hardness and elastic modulus of the matrix increase by 73.7% and 49.4%, respectively. The dynamic friction coefficient increases and the wear rate is reduced considerably after optimizing the pore structure. The wear rate, in particular, decreases by 47.7% from 2.83 × 10−8 to 1.48 × 10−8 cm3/J as the foaming agent content increases. Most importantly, this study provides an effective method to regulate the pore structure of wet friction materials, which is conducive to achieving the desired tribological properties. [ABSTRACT FROM AUTHOR]

Abstract  The increasing use of coated papers in general, but even more so in digital printing methods, reinforces the need for the properties of paper coatings to be well understood. Especially, a more detailed knowledge of the thermal properties of coatings can contribute to improved print quality and process economy of electrophotography and offset printing. Other finishing and converting operations of coated papers benefit as well. This paper proposes a model to calculate thermal conductivity based on structural parameters and the materials used. The parameters of the model are discussed and a comparison of the model parameters for a talcum and a calcium carbonate coating is given. [ABSTRACT FROM AUTHOR]

In this study, uncoated paper was characterized. Three-dimensional structure of the layer was reconstructed using imaging results of micro-CT scanning with a relatively high resolution $$(0.9~\upmu \hbox {m})$$ . Image analysis provided the pore space of the layer, which was used to determine its porosity and pore size distribution. Representative elementary volume (REV) size was determined by calculating values of porosity and permeability values for varying domain sizes. We found that those values remained unchanged for domain sizes of $$400\times 400\times 150\,\upmu \hbox {m}^{3}$$ and larger; this was chosen as the REV size. The determined REV size was verified by determining capillary pressure-saturation imbibition curves for various domain sizes. We studied the directional dependence of curves by simulating water penetration into the layer from various directions. We did not find any significant difference between curves in different directions. We studied the effect of compression of paper on curves. We found that up to 30% compression of the paper layer had very small effect on the curve. Relative permeability as a function of saturation was also calculated. Water penetration into paper was visualized using confocal laser scanning microscopy. Dynamic visualization of water flow in the paper showed that water moves along the fibers first and then fills the pores between them. [ABSTRACT FROM AUTHOR]

The variability and interdependence of local porosity and local mean geodesic tortuosity, which is a measure for the sinuosity of shortest transportation paths, is investigated at the example of the microstructure in sack paper. By means of statistical image analysis, these two morphological characteristics are computed for several cutouts of 3D image data obtained by X-ray microcomputed tomography. Considering cutouts of different sizes allows us to study the influence of the sample size on the local variability of the considered characteristics. Moreover, the interdependence between local porosity and local mean geodesic tortuosity is quantified by modeling their joint distribution parametrically using Archimedean copulas. It turns out that the family of Gumbel copulas is an appropriate model type, which is formally validated by a goodness of fit test. Besides mean geodesic tortuosity, we consider further related morphological characteristics, describing the sinuosity of those shortest transportation paths, whose minimum diameter exceeds a predefined threshold. Moreover, we show that the copula approach investigated in this paper can also be used to quantify the negative correlation between local porosity and these modified versions of local mean geodesic tortuosity. Our results elucidate the impact of local porosity on various kinds of morphological characteristics, which are not experimentally accessible and which are important for local air permeance – a key property of sack paper. [ABSTRACT FROM AUTHOR]

Nanofibrillated cellulose is obtained from cellulose resources (e.g., Natural cellulose, bacterial cellulose) and is deemed to be environmentally friendly, green, and inexhaustible. Accordingly, we reported an innovative method for fluorine-free water- and oil/grease-repellent surface based on porous cellulose-based materials. In order to improve oil/grease resistance, sulfonated nanofibrillated cellulose (SNFC) was coated on the surface to fill the porous, the obtained paper was soaked in chitosan aqueous solution as the second layer. The-SNFC-chitosan-coated paper was applied with modified polyvinyl alcohol (MPVA) as the third layer to increase water resistance and water vapour transmittance. The experimental results showed 5.2 g/m2 SNFC, 2.5 g/m2 chitosan and 7% MPVA demonstrated excellent kit rating value of 12/12 (maximum grease resistance) (oil resistance contact angle is 103.93°), good water resistance (water contact angle is 108.6°) and high water vapour transmission rate (4.8 × 10–14 g cm/cm2 s Pa) under the condition of 90% relative humidity. This non-fluorinated and practical method is an excellent alternative to existing fluorinated materials, which will further promote the development of cellulose-based packaging. [ABSTRACT FROM AUTHOR]

The porous structure of the interior of papermaking fibres is a well-known important property of the fibres. Changes of this structure will influence tensile and burst strength of paper formed from the fibres and a change in pore size of the pores within the fibre wall is also important for the ability of molecules to diffuse in and out of the fibre wall. Relevant examples of this latter effect are the removal of lignin during cooking and the addition of performance chemicals during papermaking. In this paper, pore sizes and the pore size distribution of un- bleached softwood fibres have been studied. A well-characterised fibre material consisting of laboratory cooked spruce and pine pulp of various lignin contents was used. Pore size and pore size distribution were measured by studies of the relaxation behaviour of 2H in fibres saturated with 2H20. Beside this the total and surface charge of the fibres were also measured together with strength properties of papers from unbeaten fibres. For both pulps, there is a maximum in pore radius at a yield around 46%. Calculations of fibre wall volume from water retention values and yield levels show that there is a discontinuity in pore radius as a function of the fibre wall volume around a yield of 51%. It is suggested that this discontinuity is caused by the breakdown of the hemicellulose/ lignin matrix within the fibre wall at this yield level. The strength of the papers formed from the fibres shows a correlation with the surface charge of the fibres. Based on the change in surface charge with yield and the change in total charge with yield, this correlation is suggested to be due to an opening up of the external part of the fibre wall. This stresses the importance of the chemical composition and physical structure of the outer layer of the fibre wall. [ABSTRACT FROM AUTHOR]

Graphene-nanosheet-based highly porous magnetite nanocomposites (GN-HPMNs) have been prepared using a simple solvothermal method and used as an immobilization matrix for the fabrication of a solid-state electrochemiluminescence (ECL) sensor on paper-based chips. Highly porous FeO nanocrystal clusters were coated with acrylate and wrapped tightly on the skeleton of graphene nanosheets. The structures and sizes of the GN-HPMNs could be tuned by varying the proportions of the solvents ethylene glycol and diethylene glycol. Then, the relatively highly porous ones with an average diameter of about 65 nm were combined with Nafion to form composite films on an electrode surface for immobilization of Ru(bpy) (bpy is 2,2′-bipyridine). Because of their porosity, negatively charged surface, and cooperative characteristics of magnetic nanomaterials and graphene, under an external magnetic field, the GN-HPMNs ensured effective immobilization, excellent electron transfer, and long-term stability of Ru(bpy) in the composite film. The sensor developed exhibited excellent reproducibility with a relative standard deviation of 0.65 % for 30 continuous cycles. It was found to be much more favorable for detecting compounds containing tertiary amino groups and DNAs with guanine and adenine. A detection limit (signal-to-noise ratio of 3) of 5.0 nM was obtained for tripropylamine. As an application example, 0.5 nM single-nucleotide mismatch could be detected. This was the first attempt to introduce magnetic nanomaterials and an external magnetic field into paper-based chips. The sensor developed has the advantages of high sensitivity, good stability, and wide potential applicability as well as simplicity, low cost, and good disposability. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Many of the causes of the occurrence of pathologies in reinforced concrete structures are linked to the transport of different substances through the pores and fissures of the mortar cover layer and the concrete itself. This transport is influenced by environmental factors and the properties of the porous media. This paper deals with the application of geotechnical techniques to obtain chloride transportation parameters in mortar samples. The filter paper technique was used in order to obtain the water retention curves, and column tests were performed to obtain parameters such as retard (attenuation) factor, diffusion and mechanical dispersion coefficients and permeability. These techniques proved to be useful for determining the parameters needed for modeling the transport of chloride through the concrete cover layer. Furthermore, these techniques enable the different phenomena involved (matric suction, attenuation and hydrodynamic dispersion) to be treated separately, which is useful for modeling purposes. [ABSTRACT FROM AUTHOR]

The fabrication concept for a low-cost sensor device using reduced graphene oxide (rGO) as the sensing material on a porous paper substrate is presented. The sensors were characterized using conductivity and capacitance measurements, atomic force microscopy and X-ray photoelectron spectroscopy. The effects of different reducing agents, graphene oxide (GO) flake size and film thickness were studied. The sensor was sensitive to NO, and devices based on a thin (10-nm) hydrazine-reduced GO layer had the best sensitivity, reaching a 70 % reduction in resistance after 10 min of exposure to 10 ppm NO. The sensitivity was high enough for the detection of sub-parts per million levels of NO. Desorption of gas molecules, i.e. the recovery of the sensor, could be accelerated by UV irradiation. The structure and preparation of the sensor are simple and up-scalable, allowing their fabrication in bulk quantities, and the fabrication concept can be applied to other materials, too. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Porous magnesium oxide (MgO) films on carbon fiber paper (CF) have been successfully fabricated in a hydrothermal route at different calcination temperatures. The CF@MgO samples (CF@MgO-300, -400, and -500) show different morphologies with the increasing surface area from 3 for CF to 27 m2 g−1 for CF@MgO-400. Among the four investigated samples, the CF@MgO-400 exhibits the highest phosphate removal ability (~ 1230 mg g−1) with promising applications for the large-scale utilization at low cost. [ABSTRACT FROM AUTHOR]

An overview of spectroscopic methods to investigate physical processes specific to the water-based ink/substrate interaction is made in this work. Optical techniques (as VIS reflectometry, IR-ATR and spectroellipsometry) and electrical impedance spectroscopy have been employed to study physical phenomena that describe the interaction between water-based mixtures and the substrate for printing; the latter can be absorbent (porous) or non-absorbent of liquid. Therefore, evaporation of aqueous mixtures and/or liquid penetration in porous paper are the main subjects of these studies. After brief introduction in each method, examples of various particular cases are presented and analyzed: evaporation of pure liquids and mixtures, water penetration into paper of various thicknesses, the penetration of different liquids into plain paper. The method of spectroellipsometry was used to characterize the coating of the coated paper for printing industry. [ABSTRACT FROM AUTHOR]

In this paper, we consider the propagation of chaos on bounded convex domains. Under some suitable assumptions, the empirical measure of a large number of particles on a bounded domain is shown to approximate the solution of the porous medium equation. Moreover, the propagation of chaos is derived. [ABSTRACT FROM AUTHOR]

In this paper a porous fluid-saturated cylinder subjected to a finite twist deformation is analyzed. The material of the skeleton of the porous cylinder is hyperelastic of Ogden-type and assumed nearly incompressible. The twist is applied to the cylinder in a fast rate so that the fluid pressure develops in the pores of the cylinder. The main objective of this paper is to study the stresses and the fluid pressure in the cylinder over a short period of time after the twist has been applied, or to study the initial response. The analytical expressions for the stress components and the fluid pressure are derived for Ogden material with arbitrary material parameters. The quantitative picture for the stress state is given and the signs of the normal stresses are explained. The stress arising in some imaginary fibers that were initially parallel to the axis of the cylinder is obtained. The present problem is similar to the torsion problem of a totally incompressible and nonporous cylinder in a sense that the total stresses are identical in both problems. But decomposition of the total stresses into the fluid pressure and the effective stresses, which is specific for the fluid-saturated body, can be found only using the present analysis. [ABSTRACT FROM AUTHOR]

Nonwoven-based microfluidics is an emerging field in low-cost microfluidics as another alternative to paper-based microfluidics. Comparing with the conventional paper material that has been widely used in low-cost microfluidics, the cost of nonwoven fabric material is the same range, but with the advantages of higher mechanical strength and a wider choice of chemical/physical properties. In this study, we proposed a novel method for defining a programmable and single-use wax valve on nonwoven-based microfluidic devices. The nonwoven-based microfluidic devices were fabricated using wax-printing and thermal reflow approach to define the basic microchannels for fluid penetration. Then, another layer of wax material contain valve structures were deposited on the surface of the microchannels, each wax valve structure has a corresponding heater resistor that can trigger the wax penetration to block (close) the microchannel. With the controlled thermal actuator operation, the fluid penetration inside the porous media of nonwoven fabric microchannel can be programmed with the control of wax valves. A chemical method for reopening the microchannels was also introduced in this study. The proposed programmable wax valve on nonwoven-based microfluidics is easily accessible with low-cost for point-of-care applications in biological and medical fields. [ABSTRACT FROM AUTHOR]

The influence of isopropyl alcohol and non-ionic surfactant solutions on aqueous droplet wetting behaviour on porous coated paper was determined. Paper coatings provide a micro- and nano-porous surface structure, which strictly speaking cannot be described in simple roughness terms as sub-surface lateral absorption directly impacts on the apparent contact angle. It is this very deviation from an idealised system that leads to novel wetting phenomena. Isopropyl alcohol and surfactant-based systems, both of which are commonly used in the printing industry, show differences in wetting behaviour, on both short and long timescales, with changes in the relative composition of the mixtures. Small variations of 0.1 wt% in surfactant concentration have a dramatic influence on the dynamic surface tension, and thus the wetting. It was observed that the wetting kinetics for isopropyl alcohol and surfactant solutions were different in terms of both wetting area and the penetration rate, even in cases where the dynamic surface tension of the solutions was kept the same. Different stages in the wetting and following drying processes could be observed with near infrared spectral imaging. In addition, the surfactant chemistries such as their degrees of hydrophilicity and molecular weights generated comparative differences in the wetting kinetics. The dominating factor affecting the wetting was, as expected, the solid-liquid interfacial energy defined on the practical porous substrate, which differed from the direct comparison with dynamic surface tension, thus exemplifying the deviation from idealised surface roughness behaviour when considering porous materials. An apparent 'equivalent' surface roughness value for the porous material was determined, and it was seen that an increase in this equivalent parameter enhanced the rate of wetting behaviour with decreasing solution surface tension, and so also affected the wetting evolution. The wetting was enhanced by cavities in the coating layer, which were enlarged by the penetrating liquids. [ABSTRACT FROM AUTHOR]

Porous Al SB 2 sb O SB 3 sb -Fap-TiO SB 2 sb composite ceramics were fabricated with a porosity of 50% to 53% and interconnected pores ranging between 43 and 280 µm. The compressive strength of the composites was measured to be 14 MPa to 18 MPa, which is higher than those of the human cancellous bone. Guidara et al. contributed a paper titled "Structural and mechanical properties of porous Al SB 2 sb O SB 3 sb -Fap-TiO SB 2 sb composite as a promising material for bone implants." The first part of this special topic on multiscale experiments and modeling in biomaterials and biological materials was published in June 2021. [Extracted from the article]

The present comment concerns some doubtful results included in the above paper. [ABSTRACT FROM AUTHOR]

Crystallization of salts is recognized to be a major factor of the degradation of porous materials such as stone and concrete. On the theoretical side, there is now general acceptance about the thermodynamic origin of this phenomenon. However, on the experimental side, there are only scarce quantitative data. In this respect, the reference work par excellence is that of Correns (Discuss Faraday Soc 5:267–271, ) who shows a good correlation between calculated and measured crystallization pressures. However, concerns about both the thermodynamic derivation and the experimental conditions raise the question about why Correns could have obtained such a good correlation. This issue is discussed extensively in this paper which is organized as a commented translation of a former paper by Correns, co-authored by Steinborn, and that is much richer in experimental details. [ABSTRACT FROM AUTHOR]

Realistic immiscible viscous fingering, showing all of the complex finger structure observed in experiments, has proven to be very difficult to model using direct numerical simulation based on the two-phase flow equations in porous media. Recently, a method was proposed by the authors to solve the viscous-dominated immiscible fingering problem numerically. This method gave realistic complex immiscible fingering patterns and showed very good agreement with a set of viscous unstable 2D water → oil displacement experiments. In addition, the method also gave a very good prediction of the response of the system to tertiary polymer injection. In this paper, we extend our previous work by considering the effect of wettability/capillarity on immiscible viscous fingering, e.g. in a water → oil displacements where viscosity ratio μ o / μ w ≫ 1 . We identify particular wetting states with the form of the corresponding capillary pressure used to simulate that system. It has long been known that the broad effect of capillarity is to act like a nonlinear diffusion term in the two-phase flow equations, denoted here as D (S w) . Therefore, the addition of capillary pressure, P c (S w) , into the equations acts as a damping or stabilisation term on viscous fingering, where it is the derivative of this quantity that is important, i.e. D (S w) ∼ d P c (S w) / d S w . If this capillary effect is sufficiently large, then we expect that the viscous fingering to be completely damped, and linear stability theory has supported this view. However, no convincing numerical simulations have been presented showing this effect clearly for systems of different wettability, due to the problem of simulating realistic immiscible fingering in the first place (i.e. for the viscous-dominated case where P c = 0 ). Since we already have a good method for numerically generating complex realistic immiscible fingering for the P c = 0 case, we are able for the first time to present a study examining both the viscous-dominated limit and the gradual change in the viscous/capillary force balance. This force balance also depends on the physical size of the system as well as on the length scale of the capillary damping. To address these issues, scaling theory is applied, using the classical approach of Rapport (1955), to study this scaling in a systematic manner. In this paper, we show that the effect of wettability/capillarity on immiscible viscous fingering is somewhat more complex and interesting than the (broadly correct) qualitative description above. From a "lab-scale" base case 2D water → oil displacement showing clear immiscible viscous fingering which we have already matched very well using our numerical method, we examine the effects of introducing either a water wet (WW) or an oil wet (OW) capillary pressure, of different "magnitudes". The characteristics of these two cases (WW and OW) are important in how the value of corresponding D (S w) functions, relate to the (Buckley–Leverett) shock front saturation, S wf , of the viscous-dominated ( P c = 0 ) case. By analysing this, and carrying out some confirming calculations, we show clearly why we expect to see much clearer immiscible fingering at the lab scale in oil wet rather than in water wet systems. Indeed, we demonstrate why it is very difficult to see immiscible fingering in WW lab systems. From this finding, one might conclude that since no fingering is observed for the WW lab-scale case, then none would be expected at the larger "field" scale. However, by invoking scaling theory—specifically the viscous/capillary scaling group, C VC1 , (and a corresponding "shape group", C S 1 ), we demonstrate very clearly that, although the WW viscous fingers do not usually appear at the lab scale, they emerge very distinctly as we "inflate" the system in size in a systematic manner. In contrast, we demonstrate exactly why it is much more likely to observe viscous fingering for the OW (or weakly wetting) case at the lab scale. Finally, to confirm our analysis of the WW and OW immiscible fingering conclusions at the lab scale, we present two experiments in a lab-scale bead pack where μ o / μ w = 100 ; no fingering is seen in the WW case, whereas clear developed immiscible fingering is observed in the OW case. [ABSTRACT FROM AUTHOR]

The impact of fluid inertia on fracture flow dynamics, particularly under high-velocity conditions, has emerged as a critical consideration in petroleum engineering and related fields. This review paper investigates the profound effects of inertia-dominated nonlinear flow, a phenomenon increasingly recognised for its significant influence on fluid dynamics in rock fractures. Given the prevalence and importance of such flows in field applications, neglecting fluid inertial effects is no longer justifiable. A comprehensive investigation into these effects is essential for advancing our understanding of fracture flow mechanisms and optimising engineering practices. This review aims to thoroughly analyse the impact of fluid inertia on applications in hydraulic fracturing. It offers an in-depth discussion of how fluid inertia affects critical aspects of crack propagation, fracture diagnostics, proppant transport and settlement, and fines migration. Additionally, this paper identifies and explores four main factors that influence the fluid inertia effect in fracture flows: fracture roughness, intersections and dead ends within the fracture network, variations in contact area and fracture aperture, and the role of shear displacement. The review provides valuable insights into the complex interplay between fluid inertia and fracture flow dynamics by elucidating these factors. [ABSTRACT FROM AUTHOR]

Rock permeability is a critical parameter for assessing rock's ability to facilitate fluid flow. The pressure pulse decay method, characterized by its short testing duration and high accuracy, is widely employed for permeability testing of low-permeable rocks. This method acquires pressure differential data by conducting experiments on regular-shaped samples. Due to the theoretical solution's requirements (cross-sectional area and length), this method cannot be applied to rocks that are challenging to shape into regular samples, such as soft rock and soft coal. In this paper, a novel permeability determination method based on the numerical simulation of inverse problem is proposed. This method involves constructing a mathematical model that accurately describes the entire process of determining permeability using the pressure pulse decay method. The sample's pressure difference data over time is used as a penalty function, and the sample permeability is calculated by inverse problem numerical simulation. Specifically, a computation strategy is introduced to determine the initial range for permeability, aiming to avoid locally optimal issues in the inverse problem numerical simulation. Utilizing the new model, forward and inverse problem numerical simulations were conducted. The pressure difference decay data obtained from these calculations closely match the laboratory-measured data for regular samples, with correlation coefficient (R2) reaching 0.992 and 0.990, respectively. The permeability calculated by inverse simulation is determined to be 0.28 mD, showing minimal deviation from the theoretically derived permeability. This demonstrates the accuracy of the proposed model in describing the experimental process of the pressure pulse decay method and the precision of the obtaining permeability parameters. Furthermore, when applied to numerical experiments with irregular-shaped samples, the inverse simulation yields pressure difference data that closely matches the experimental data. The established new method effectively addresses limitations posed by the shape of samples, providing a novel approach for measuring rock permeability. The convenience of numerical experiments also offers a new and efficient means to investigate the competitive effects of permeability influencing factors. This provides promising applications in unconventional gas development, depleted reservoir carbon dioxide storage, and geological hydrogen storage, among other fields. Highlights: A mathematical model is developed to accurately describe gas mass transfer behaviour during the permeability testing by the transient method. A computational method for calculating permeability based on numerical solution is proposed. The new method proposed in this paper solves the limitation of the traditional method for the shape of the test sample. [ABSTRACT FROM AUTHOR]

Polymer flooding is a prominent chemical enhanced oil recovery (CEOR) method that involves the injection of polymer solution into the oil reservoirs to improve the sweep efficiency and maximize the ultimate oil recovery. Selecting an appropriate polymer type, molecular weight, and concentration is crucial for success of any polymer flooding project. This paper studies the flow behavior of HPAM-based EOR polymers with different molecular weights through porous media. Dynamic adsorption and injectivity tests were performed through 5 Darcies sandpacks using polymer solutions prepared with low (LM; 8–10 MDa) and high (HM; 20–25 MDa) molecular weight polymers. Polymer solutions with different target viscosity values of 7, 15 and 30 cP were flooded through sandpacks at the reservoir temperature of 80 ºC and pore pressure of 1000 psi. The results showed that HM solutions with different target viscosity have higher polymer retention through sandpacks compared to LM solutions. Furthermore, results of residual resistance factor (RRF) measurements were in line with dynamic adsorption tests results. That is, permeability reduction due to irreversible polymer retention was higher when HM polymer solutions were injected. Furthermore, the results showed that although the resistance factor (RF) and in-situ viscosity of HM and LM polymers are in the same range, however, shear thickening regime becomes pronounced in the case of HM polymer with higher target viscosity. Polymer relaxation time measurements, and consequently, Deborah number calculations were performed to describe the shear thickening behavior by polymers viscoelastic characteristics. Results demonstrate that occurrence of shear thickening regime is controlled by Deborah number which is a function of polymer molecular weight, polymer concentration and injection rate. These results shed light on the importance of the selection of optimal polymer molecular weight and concentration during the design of polymer flooding projects. [ABSTRACT FROM AUTHOR]

Lightweight porous structural materials have excellent energy absorption performance, and their application are gradually appeared. This paper takes the shock-absorbing material of nuclear equipment transportation casks as the starting point, and manufactures an orthogonal trapezoidal aluminum honeycomb by welding (WOTAH). The mechanical properties with different cell thicknesses and cell size ratios under different impact loads are studied through experimental and simulation methods, and the deformation process and energy absorption performance of the materials are obtained. The energy absorption performance of materials under quasi-static loading was investigated using plastic deformation theory and compared with experimental results. Based on the experimental results, the least squares method was used for data fitting to obtain the C-S dynamic constitutive relationship of the material. The equivalent structure was used to replace the honeycomb structure for simulation, and the influence of strain rate effect and structural size on material properties was further studied. Through the above mechanical performance analysis and comparison with wood, it is shown that WOTHA has feasible for the application of nuclear equipment impact limiter. [ABSTRACT FROM AUTHOR]

The European Physical Journal: Special Topics presents a collection of fifteen papers focusing on recent advancements in composite materials and structures for energy applications. The papers cover topics such as microfluidics-integrated smart acoustic metamaterials, dusty tetra-hybrid Casson nanofluid flow, thermosolutal convection of Cu/water micropolar nanofluid, and the mechanical behavior of electroactive polymers in thermal environments. Other studies include the synthesis and sintering of ZrB2, plasma-enhanced electrodes for hydro-oxy fuel generators, and the relationship between water injection volume and liquid injection pressure in pipeline deformation. The research explores various aspects of materials science and engineering, offering insights into innovative applications and advancements in the field. [Extracted from the article]

The paper is devoted to the study of magnetic properties of magnetic colloids placed in porous media. The importance of this study is due to the development of new applications of such media. The paper presents the results of an experimental study of the temperature and frequency dependences of the magnetic susceptibility of magnetic colloids on different bases placed in a porous medium. For this purpose, a kerosene-based magnetic colloid and a water-based magnetic colloid were used. White electrocorundum was used as a porous medium. Magnetic susceptibility was studied by the bridge method in a wide range of frequencies and temperatures. It was found that the frequency and temperature dependences of magnetic susceptibility of bulk and magnetic colloids placed in porous media significantly differ depending on the pore size. The explanation of the obtained results is based on the assumption of the influence of surface forces on the relaxation processes of the magnetic moment of colloidal particles. [ABSTRACT FROM AUTHOR]

The paper presents the results of investigation into the effects of the composition of a nonwetting liquid (distilled water, physiological solution, and doxorubicin solution) on the kinetics of outflow from hydrophobized Fluka 100 C18 silica gel. A series of measurements was taken regarding the filling of and discharge from the investigated systems in the temperature range of 5 to 40°C with the waiting time between cycles 10–1000 s. Values were obtained for the fraction of the liquid that failed to flow out of a porous material as a function of time and temperature, and also the functions of pore size distribution were recovered for the retained liquid. A reduction was found in the fraction of the retained liquid with increase in temperature and the waiting time. It follows from the obtained results that the determination of the outflow kinetics for a doxorubicin solution with a concentration of up to 1 μM can be carried out without using a medicinal drug. [ABSTRACT FROM AUTHOR]

Viscous fingering in porous media occurs when the (miscible or immiscible) displacing fluid has a lower viscosity than the displaced fluid. For example, immiscible fingering is observed in experiments where water displaces a much more viscous oil. Modelling the observed fingering patterns in immiscible viscous fingering has proven to be very challenging, which has often been identified as being due to numerical issues. However, in a recent paper (Sorbie et al. in Transp. Porous Media 133:331–359, 2020) suggested that the modelling issues are more closely related to the physics and formulation of the problem. They proposed an approach based on the fractional flow curve, f w ∗ , as the principal input, and then derived relative permeabilities which give the maximum total mobility. Sorbie et al. were then able to produce complex, well-resolves immiscible finger patterns using elementary numerical methods. In this paper, this new approach to modelling immiscible viscous fingering is tested by performing direct numerical simulations of previously published experimental water/oil displacements in 2D sandstone porous media. Experiments were modelled at adverse viscosity ratios ( μ o / μ w ), with oil viscosities ranging from μo = 412 to 7000 cP, i.e. for a viscosity ratio range, ( μ o / μ w ) ∼ 400–7000. These experiments have extensive production data as well as in situ 2D immiscible fingering images, measured by X-ray scanning. In all cases, very good quantitative agreement between experiment and modelling results is found, providing a strong validation of the new modelling approach. The underlying parameters used in the modelling of these unstable immiscible floods, the f w ∗ functions, show very consistent and understandable variation with the viscosity ratio, ( μ o / μ w ). [ABSTRACT FROM AUTHOR]

The digital core and pore network model (PNM) are the basis of studying porous media. At present, the voxel-based maximal ball (MB) method has been widely used in the construction of PNM. However, due to the dependence on discrete data and the fuzziness of size definition, the PNM by using this method may not be accurate. The construction of PNM is essentially a geometric problem. Therefore, a computational geometry method was proposed in this paper to construct the PNM. A grid-based core surface model was constructed by using the moving cubes (MC) algorithm, the maximal inscribed ball of the grid space was extracted by using the computational geometry method, and a PNM was built by judging 12 types of dependency relationships of the master and servant spheres in the inscribed ball. Finally, combined with Berea sandstone, the physical parameters of cores obtained by the proposed method and the MB method were compared. The throat length results show that the proposed algorithm has improved the defect of small throat length when the MB method is used to partition core pore space. Meanwhile, the results of other parameters tend to be consistent, which proves the reliability of the proposed algorithm. Besides, by comparing the seepage simulation results of the two methods with the physical experiments, it was proved that the permeability calculated by the method in this paper is closer to the measured value of the physical experiment than that by the MB method. [ABSTRACT FROM AUTHOR]

There are limited comparative studies on modeling fluid transport in fractured porous media. Hence, this paper systematically compares the steady-state creeping flow Stokes–Brinkman and Darcy–Darcy models for computational efficiency and accuracy. Sensitivity analyses were also conducted on the effect of fracture orientations, fracture sizes, mesh resolution, and fractures with Local Grid Refinement (LGR) under the FEniCS computational framework. Both models were validated numerically, and the accuracy of their solution is compared using the R-squared metric and L2 norm estimates. Key results showed that both models have similar pressure and velocity field solutions for a given fracture orientation. The computational time required for solving the Stokes–Brinkman models for a single fracture case was unusually lower than that of the Darcy–Darcy model when the pressure and velocity terms in the Darcy–Darcy model were solved simultaneously using two equations, contrary to where only one equation solves for the pressure and the velocity is obtained by projecting the gradient of pressure onto a vector space. The Stokes–Brinkman model is more sensitive to mesh resolution, and as a result, the Darcy–Darcy model tends to be more accurate than the Stokes–Brinkman model at low resolutions. Local Grid Refinement (LGR) can improve the Stokes–Brinkman model's accuracy at low mesh resolution. Furthermore, both models showed similar results when compared for complex fracture systems such as multiple fracture cases: interconnecting and isolated fractured porous media systems under low-velocity and steady-state creeping flow conditions. The FEniCS code in this paper is shared for future researchers to reproduce results or extend the research work. [ABSTRACT FROM AUTHOR]

In this attractive paper (Battiato et al. in Transp Porous Media, 2019), the authors review different methods of upscaling heterogeneous media descriptions to continuous macroscopic equivalent descriptions. I would like to introduce some comments to complete the presentation of the homogenisation theory in Section 7. [ABSTRACT FROM AUTHOR]

Since the internal structure of actual porous media has irregularity and complexity and is rough on the surface, it cannot be characterized accurately by traditional theoretical analytical methods. In this paper, the mathematical formalism of the effective diffusion coefficient of gas on rough porous surfaces is established by employing fractal geometry theory, utilizing the rough capillary tube bundle model, and introducing the penetration correction factor. The effective gas diffusion coefficient is investigated as a function relation of the rough porous media structural parameters and gas parameters. The results show that the effective diffusion coefficient of gas is positively correlated to the porosity, maximum pore diameter, and area fractal dimension of porous media and negatively correlated to the relative roughness, tortuous fractal dimension, the molar mass of gas, and gas density. The correctness and reliability of the present model have been confirmed, by the comparative analysis of the model predictive values in this paper and the available experimental data. [ABSTRACT FROM AUTHOR]

Multiple flow mechanisms that coexist in nanoscale porous media are responsible for deviations from the linear Klinkenberg equation. The use of mathematical models in the literature has obvious limitations in evaluating this flow phenomenon because the viscosity/diffusion coefficients of nanoscale porous media are more accurate only in the limited Knudsen number region. By introducing, the concept of an effective molecular mean free path, this paper proposes single models of viscosity/diffusion for the full Knudsen number range to replace the combination model in the literature. On this basis, a new apparent permeability model is developed with multiple coexisting mechanisms for the full Knudsen number range, and the effectiveness of the proposed model is verified by using published data. The discontinuous problem of the combination model of the viscosity/diffusion coefficient in the literature for the full Knudsen number range is solved using the new viscosity and diffusion coefficient models. The new apparent permeability model accurately predicts the absolute permeability and explains the phenomenon of deviation from the linear Klinkenberg equation. This paper further discusses the influence of different mechanisms on the permeability. The rarefaction effect weakens the diffusion ability in porous media but increases the contribution of Darcy flow to permeability. The viscous flow increment, absolute permeability and slippage effect were the most important flow mechanisms in nanopores. Article Highlights: We present the equation of the gas viscosity/diffusion coefficient in nanopores for the full Knudsen number range. We present a new apparent permeability model with multiple coexisting mechanisms for the full Knudsen number range. Our model predicts the absolute permeability of nanoscale porous media. [ABSTRACT FROM AUTHOR]

This paper aims to derive the motion equations for a small-scale flexoelectric-multilayer plate and move deep through its vibrational response to several determining variable variations. Flexoelectricity indicates the electrical polarization induction in response to the non-uniform strain gradient. As moving toward small scales, the importance and the role of this property comes more to the picture. The under-examination structure is fabricated of three layers; a mid-layer which is assumed to be composed of the porous exponential and power law-functionally graded materials, two flexoelectric face sheets, and the Vlasov foundation. The motion equations are derived mathematically based on the new EP of porous material, Hamilton's principle, and modified couple stress theory. Utilizing the new EP power law besides evaluating the influence of the variables, length scale parameter, materials composition, geometrical characteristics, porosity, foundation parameter, and boundary conditions (B.C.s) on the dimensionless natural frequency (DNF) of such a sandwich model is the novelty of this paper. It is revealed that the lateral ratio enhancement causes DNF and stiffness reduction in the model. Furthermore, among all considered B.C.s, simply support and clamped support refer to the lowest and the highest DNF, respectively. The content of the recent paper serves as a good source to provide a better understanding of the vibrational response of high stiffness-to-weight ratio structures to different variable variations. [ABSTRACT FROM AUTHOR]

The efficient characterization of material properties of porous multi-phase sintered steels by instrumental indentation is still an open question. To the authors' knowledge, so far only a characterization of single-phase porous sintered steel by nanoindenation has been reported in literature. This paper for the first time offers a study about the applicability of microindentation techniques for characterizing the matrix material in a multi-phase sintered steel. This preliminary study is motivated by the relatively wide availability of necessary equipment, and simplicity of material identification procedures. Herein, a dual-phase ferrite/bainite Astaloy steel with 9% porosity is studied. Various commonly used methods for the reconstruction of stress–strain curves from microindentation data are considered, whereby both Vickers and spherical tips are used. In addition, some homogeneous solid materials are investigated to better asses the performance of applied identification procedures. Two approaches for the mesoscale identification of the considered sintered steel are attempted. The first one is based on the identification of individual material phases, while in the other one the homogenization of the metallic matrix is adopted. To assess the reliability of obtained parameters, the direct numerical simulation of representative volume elements of realistic steel microstructure subjected to uniaxial tension is conducted. Numerical results are compared with the data from the macroscopic uniaxial tensile test. The obtained results indicate that microindentation is adequate for the identification of elastic properties of individual material phases, but results for local plastic parameters are largely inconclusive and a further analysis is needed, focusing on applying smaller forces and investigating the influence of pores on identification results. Nevertheless, it seems that macroscopic stress–strain curves could be captured more accurately by the methodology based on the matrix homogenization if relatively large indentation forces are applied. [ABSTRACT FROM AUTHOR]

Abstract  The porous structure and hydrophilic-hydrophobic properties of the gas diffusion layers (GDL) of electrodes on a substrate of carbon paper in proton-exchange membrane fuel cells have been investigated with the methods of standard porosimetry and of pycnometry. GDL containing various fluoroplast concentrations were impregnated with water, and this process has been investigated at 20 and 80°C. The impregnation rate is significantly higher for untreated carbon paper than for teflonated GDL and also increases significantly with increasing temperature. With teflonization of the carbon paper, hydrophilic porosity decreases, while hydrophobic porosity increases. This increase, however, ceases at high fluoroplast concentrations. The concept of hydrophobization effectiveness of the porous carbon substrate of GDL is introduced. It has been established that hydrophobization effectiveness decreases with increasing fluoroplast concentration and depends on the type of suspension. Curves of the angle of wetting of GDL by water versus the pore radius exhibit a minimum. Different values of the angle of wetting of GDL by water in different pores are explained by nonuniform distributions of both fluoroplast particles and hydrophilic surface groups in pores of different dimensions. [ABSTRACT FROM AUTHOR]

In a pore network model, microscopic moisture storage and transport processes are modeled at pore level after which this information is extrapolated to obtain macroscopic properties describing the material's moisture behavior. Such a model is typically validated by comparing measured and simulated macroscopic properties. However, due to the uncertainty associated with the experimental property determination, a possibly incorrect description of the model's microscopic processes can be overlooked. Assessing the model's ability to correctly simulate the moisture behavior at pore level is therefore required for its complete validation. To this aim, the moisture stored in the individual pores of unsaturated materials is imaged with the help of X-ray computed tomography images and compared to the moisture distribution simulated with a pore network model. The acquired X-ray computed tomography images clearly show the evolution of the drying process, wherein emptied pores retain water in their irregularly shaped corners. While some corners do not store any moisture, others allow a maximum of 10 % of the pore's volume to be filled with corner islands. By comparing these images with the pore network model, however, it becomes clear that the amount of water, trapped in these pore corners is heavily overestimated in the model's current implementation. Since this implementation is commonly used in existing pore network models, this paper proves the need of a detailed investigation of the corner islands in real porous media to formulate a different way of calculating moisture storage in pore corners. Article Highlights: Visualising the distribution of moisture in unsaturated material using X-ray computed tomography Microscopic validation of a pore network model by comparing the simulated moisture storage in the individual pore bodies and throats with X-ray computed tomography images of unsaturated material. Proof of the limitations of the pore network model with regards to moisture storage in pore corners and recommendations for possible model improvement. [ABSTRACT FROM AUTHOR]

The paper considers equations describing the motion of a fluid in a porous medium under the action of an electric field in conditions of the formed turbulent mode of motion. Equations are given that describe the acoustic oscillations that occur in a fluid, the source of which can be not only an alternating, but also a constant electric field. The pulsating broadband acoustic oscillations arising under the action of a constant electric field can be spurious during the operation of electroacoustic transducers, which should be taken into account in their design. The results of field experiments on the model of an electroacoustic transducer confirm the theoretical results presented in the study. The stated theoretical and experimental results make it possible to solve the priority scientific–technical problem of designing and creating new types of acoustic emitters. [ABSTRACT FROM AUTHOR]

In this study, geomechanical behavior of fractures and faults in rocks as a saturated deformable discrete fracture-porous medium has been evaluated using coupled fluid flow-geomechanics numerical modeling. The purpose of this paper is to observe and evaluate the effects of fractures and faults on the pore pressures during fluid flow through reservoirs. This issue involves solving the equations that have been derived from the Biot consolidation theory such as fluid mass balance equation, Darcy law and momentum balance equations. Govern coupled equations were solved using the standard Galerkin finite element method for continuous porous medium. Elements called "zero-thickness elements" were also used to discretize the fault as a discontinuous part of the porous medium. In compared with the previous and similar methods, the method introduced in this paper, made modifications in either the choice of the element and the method of solving the governing equations. The main advantage of this paper is providing clear precise formulations of the double node zero-thickness element in hydro-mechanical modeling of fractures and faults. Verification of the proposed process and models presented in this paper were done by providing three index problems which their analytical and numerical solutions are available. The results of our model provide a good agreement to these reference solutions which indicates the accuracy of the method presented in this paper. [ABSTRACT FROM AUTHOR]

Reservoir simulation is crucial for understanding the flow response in underground reservoirs, and it significantly helps reduce uncertainties in geological characterization and optimize methodologies for field development strategies. However, providing efficient and accurate solutions for the strong heterogeneity remains challenging, as most of the discretization methods cannot handle this complexity. In this work, we perform a comprehensive assessment of various numerical linearization techniques employed in reservoir simulation, particularly focusing on the performance of the nonlinear solver for problem dealing with fluid flow in porous media. The primary linearization methods examined are finite difference central (FDC), finite forward difference (FDF), and operator-based linearization (OBL). These methods are rigorously analyzed and compared in terms of their accuracy, computational efficiency, and adaptability to changing reservoir conditions. The results demonstrate that each method has distinct strengths and limitations. The FDC method is more accurate particularly in complex simulations where strong heterogeneity are introduced but is generally slower in convergence. The OBL on the other hand, is more efficient and converges quickly, which makes it suitable for scenarios with limited computational resources and simple physics, while the FDF method provides a balanced combination of precision and computational speed, contingent upon careful step size management of the derivative estimations. This paper aims to guide the selection of appropriate linearization techniques for enhancing nonlinear solvers' accuracy and efficiency in reservoir simulation. [ABSTRACT FROM AUTHOR]

In this paper, the capillary is divided into several regions, and the effective pore radius is proposed. The relationship between the effective hole radius and the maximum radius is analyzed. The fractal models of fractal flow rate, average velocity and effective permeability of power-law fluid flow in fractal soil composed of circular cross section capillaries are derived. The effects of different power exponent, viscosity coefficient and fractal dimension on the average flow velocity and effective permeability model are analyzed, and the comparative analysis of different sections is carried out. The reasonable calculation results of the fractal model given in this paper verify the correctness of the model. The introduction of the effective pore radius concept and the derivation of fractal models have advanced our ability to characterize and predict flow behavior. We anticipate that these findings will stimulate further research and practical applications in various domains, benefiting both scientific knowledge and technological advancements. [ABSTRACT FROM AUTHOR]