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Tool grinding is a fundamental process step when manufacturing cylindrical cemented carbide tools. A deeper understanding of the relationship between heat generation, heat transfer and fluid dynamics is essential to optimize the application of cooling lubrication. Due to the porous structure of the grinding tool as well as the rough surfaces of tool and workpiece, this inherently leads to multiscale problems. In this paper, an approach for modeling the heat transfer between the grinding tool, the workpiece and coolant on the microscale and mesoscale is introduced, including the effective influence of the porous structure. As a basis for the simulations, experimental investigations are conducted using individual abrasive grains. A linear relationship between the single grain chip cross section and the tangential force is established with an average RMSE of 1.421 N, allowing the total heat flux to be calculated. The results are then transferred to continuous and discontinuous 2D multiscale fluid dynamic simulations in order to predict heat generation and to potentially optimize the cooling lubrication in grinding processes.

Determining pore sizes of porous media accurately is essential for many reasons. The standard ASTM F316 describing calculations used in gas-liquid displacement (GLD) porometry includes a factor B or a capillary constant. The standard does not explain the nature of this factor and the reasons for using its value. This work aims to investigate the capillary constant and to understand its meaning and applicability in calculating the pore diameter. Another goal is to assess the pore diameter measured in GLD porometry by comparing it with pore diameters measured with image analysis and cut point test methods. Seven filter media samples with as simple a structure as possible were analyzed. An investigation of the capillary constant revealed at least five different approaches, of which all are by no means applied for the calculations of pore size. Using the approach described in standard ASTM F316 to adjust the values obtained by GLD porometry was found unsuitable for the simply structured samples studied in this work. This work shows that the pore diameters measured by GLD porometry are most comparable with the other studied techniques when using Silwick as the wetting liquid. The raw data of bubble point pore and mean flow pore diameters measured by GLD porometry are similar to the largest pore sizes and mean pore diameters measured by image analysis and cut point test methods. This, in turn, confirms the absence of the need to use any constants for calculating the pore diameters for the samples studied in this work. Post-print / Final draft

The object of research in the paper is the process of fluid transfer through the pore space of the reservoir rock. The traditional method of assessing reservoir properties has a significant number of sources of uncertainty. In this article, to compensate for the shortcomings of the existing method of reservoir characterization, an algorithm of actions is proposed with an increase in the accuracy and representativeness of its results. The workflow of the pre-alpha version of the software for the existing pore space representation algorithm is presented. In this work, the step-by-step actions necessary to create an application that can reproduce the pore space and mass transfer processes in it by reading the data of the magnetic resonance imaging(MRI)of the rock were analytically determined. In particular, the use of ready-made open code is proposed, which displays the rock according to the pictures and also reproduces the fluid flow processes in the rock reservoir. Still, there is no adapted framework for the ordinary user. The use of such an application, proposed by the authors, will lead to a much lower degree of the reservoir properties uncertainty, will help to more reliably reflect the reservoir properties of the reservoir rock, and provide a more reliable impression of the reservoir operation at the design stage of its development. The proposed software, based on already existing developments in open access on the GitHub platform, will help the user to fully use the existing tools for building a three-dimensional model of a porous sample based on the data of MRI images of the rock. After finalizing the user interface with the help of the user interface design and front-end development, the engineering staff will be able to conduct research on the rock at a macroscopic level.

The aim of this study is to develop a numerical package that can simulate sound propagation in different media including air, water, porous materials, and metamaterials. Finite-difference time-domain (FDTD) method along with the immersed-boundary (IB) method are implemented in the realistic physical time and space domains for the purpose of numerically computing complex geometries with multiple media. The simulations include material changes such as air-water or air-porous material interfaces. Several applications are simulated in the regime of sound waves scattered by single to multiple air bubbles underwater and moving sources over complex structures. Those studies can be extended to real life applications such as fish bladder simulation, ocean geography, or migrating noise from flying-over unmanned aerial vehicles (UAVs) and domestic airplanes. Complex geometries are considered in the simulations including pulsing bubbles and geometries based on buildings. This package is capable of simulating events that previous numerical solvers or experiments were unable to perform. Novel discoveries, such as the interior gas motion of the bubbles, touching and merging bubbles, and phenomena from a moving source over different geometries and materials, are presented.

The work described in this thesis mainly concerns the development and implementation of nuclear magnetic resonance (NMR) methods to provide quantitative information on chemical conversion within a novel NMR compatible trickle-bed reactor (TBR). Techniques to map the distribution of chemical species within a catalyst bed were implemented under non-steady state and steady state conditions. Batch reactions were carried out to benchmark a simple aromatic hydrogenation reaction (styrene) and more complex reactions, such as aromatic nitrile hydrogenations (benzonitrile and phthalonitrile) over a Pd/Al2O3 catalyst. These were subsequently tested in the continuous flow TBR under near-ambient conditions. Batch reactions revealed information on the inter- particle chemical kinetics, conversion, and selectivity for the desired reactions. Non-spatially resolved and spatially resolved 2D NMR relaxation and diffusion correlations along with spectroscopic techniques were used to extract intra-particle chemical kinetics both under non-steady state and steady state conditions. These were compared with chemical compositions retrieved from the outlet of the TBR. The Modified Total Generalised Variation (MTGV) regularisation technique was developed to improve the resolution of 2D NMR correlations and verified against a more established technique. Compressed sensing was also implemented to increase temporal resolution of 2D spectroscopic methods. This work improves the understanding of catalytic reactors and contributes to the advancement of magnetic resonance to investigate complex, multi-component reactions relevant to the agricultural and chemical industry.

As an extension to the well-established stationary elliptic partial differential equation (PDE) with random continuous coefficients we study a time-dependent advection-diffusion problem, where the coefficients may have random spatial discontinuities. In a subsurface flow model, the randomness in a parabolic equation may account for insufficient measurements or uncertain material procurement, while the discontinuities could represent transitions in heterogeneous media. Specifically, a scenario with coupled advection and diffusion coefficients that are modeled as sums of continuous random fields and discontinuous jump components are considered. The respective coefficient functions allow a very flexible modeling, however, they also complicate the analysis and numerical approximation of the corresponding random parabolic PDE. We show that the model problem is indeed well-posed under mild assumptions and show measurability of the pathwise solution. For the numerical approximation we employ a sample-adapted, pathwise discretization scheme based on a finite element approach. This semi-discrete method accounts for the discontinuities in each sample, but leads to stochastic, finite-dimensional approximation spaces. We ensure measurability of the semi-discrete solution, which in turn enables us to derive moments bounds on the mean-squared approximation error. By coupling this semi-discrete approach with suitable coefficient approximation and a stable time stepping, we obtain a fully discrete algorithm to solve the random parabolic PDE. We provide an overall error bound for this scheme and illustrate our results with several numerical experiments., ESAIM: Mathematical Modelling and Numerical Analysis, 56 (5), ISSN:2822-7840, ISSN:2804-7214

We provide a rigorous workflow to quantify the effects of key sources of uncertainty associated with equivalent fracture aperture estimates w constrained through mud loss information acquired while drilling a well in a reservoir. A stochastic inverse modeling framework is employed to estimate the probability distribution of w. This choice is consistent with the quantity and quality of available data. The approach allows assessing the probability that values of w inferred from mud loss events exceed a given threshold. We rely on a streamlined analytical solution to model mud losses while drilling. We explicitly consider uncertainties associated with model parameters and forcing terms, including drilling fluid rheological properties and flow rates, pore fluid pressure, and dynamic drilling fluid pressure. A synthetic scenario is considered to provide a transparent reference setting against which our stochastic inverse modeling workflow can be appraised. The approach is then applied to a real-case scenario. The latter is associated with data monitored on a rig site. A direct comparison of the impact of data collected through two common techniques (respectively, relying on flow meter sensors or pump strokes) on the ensuing probability of w is provided. A detailed analysis of the uncertainty related to the level of data corruption is also performed, considering various levels of measurement errors. Results associated with the field setting suggest that the proposed workflow yields probability distribution of w that are compatible with interpretations relying on traditional analyses of image logs. Results stemming from direct and indirect flow data display similar shapes. This suggests the viability of the probabilistic inversion methodology to assist quasi-real-time identification of equivalent fracture apertures on the basis of routinely acquired information during drilling.

Hypothesis Transport of suspended colloids in heterogeneous porous media is a multi-scale process that exhibits anomalous behavior and cannot be described by the Fickian dispersion theory. Although many studies have documented colloids’ transport at different length scales, a theoretical basis that links pore- to core-scale observations remains lacking. It is hypothesized that a recently proposed pore-scale statistical kinetic theory is able to capture the results observed experimentally. Experiments We implement a multi-scale approach via conducting core-flooding experiments of colloidal particles in a sandstone sample, simulating particles flowing through a sub-volume of the rock’s digital twin, and developing a core-scale statistical theory for particles’ residence times via upscaling the pore-scale kinetic theory. Experimental and computational results for solute transport are used as benchmark. Findings Based on good agreement across the scales achieved in our investigation, we show that the macroscopically observed anomalous transport is particle-type dependent and stems from particles’ microscopic dispersion and deposition in heterogeneous flow fields. In particular, we reveal that residence-time distributions (i.e., breakthrough curve) obey a closed-form function that encompasses particles’ microscopic dynamics, which allows investigations of a whole transition from pre-asymptotic to asymptotic behavior. The physical insights attained could be useful for interpreting experimental data and designing colloidal tracers.

A two-dimensional (2-D) double-distribution lattice Boltzmann method (LBM) is implemented to study isothermal drying of a colloidal suspension considering local nanoparticle effects. The two LBMs solve isothermal two-phase flow and nanoparticle transport, respectively. The three local nanoparticle effects on the fluid dynamics considered in this paper are viscosity increase, surface tension drop and local drying rate reduction. The proposed model is first validated by the study of the drying of a 2-D suspended colloidal droplet for two different Péclet numbers, where the evolution of the diameter squared agrees well with experimental results. The model is further validated looking at drying of a colloid in a 2-D capillary tube with two open ends. Compared with experimental results, the best agreement in terms of deposition profile and drying time is obtained when considering all three nanoparticle effects. Afterwards, we apply the model to investigate the complicated drying of a colloidal suspension in a 2-D porous asphalt, considering all three local nanoparticle effects. The drying dynamics, resultant nanoparticle transport, accumulation and deposition are first analysed for a base case. Then a parametric study is conducted varying the initial nanoparticle concentration, porous medium contact angle, nanoparticle contact angle and nanoparticle diffusion coefficient. The influence of these parameters on drying dynamics, drying rate, deposition process and final deposition configurations is analysed in detail, together with the mutual influence of local nanoparticle behaviour. Finally, a unified relation between the average drying rate and the studied parameters is proposed and verified, covering the full parameter ranges of simulations., Journal of Fluid Mechanics, 963, ISSN:0022-1120, ISSN:1469-7645

We introduce a new approach for modelling the swelling, drying and elastic behaviour of hydrogels, which leverages the tractability of classical linear-elastic theory whilst incorporating nonlinearities arising from large swelling strains. Relative to a reference state of a fully-swollen gel – in which the polymer scaffold may only comprise less than 1% of the total volume – a constitutive model for the Cauchy stress tensor is presented, which linearises around small deviatoric strains corresponding to shearing deformations of the material whilst allowing for a nonlinear relation between stress and isotropic strains. Such isotropic strains are considered only to be a consequence of losses and gains of water, while the hydrogel is taken to be instantaneously incompressible. The dynamics governing swelling and drying are described by coupling the interstitial flow of the water through the porous gel with the elastic response of the gel. This approach allows for a complete description of gel behaviour using only three macroscopic polymer-fraction-dependent parameters: an osmotic modulus; a shear modulus; and a permeability. It is shown how these three material parameters can, in principle, be determined experimentally using a simple rheometry experiment in which a gel is compressed between two plates surrounded by water and the total force on the top plate is measured. To illustrate our approach, we solve for the swelling of a gel under horizontal confinement and for a partially-dried hydrogel bead placed in water.

We consider the multidirectional swelling and drying of hydrogels formed from super-absorbent polymers and water, focusing on the elastic deformation caused by differential swelling. By modelling hydrogels as instantaneously incompressible linear elastic materials and considering situations in which there can be large isotropic strains (arising from swelling), while deviatoric strains remain small, it is possible to describe accurately a wider range of gel states than traditional linear elastic theories allow. An equation is derived relating the displacement field to the polymer fraction in such hydrogels, permitting the shape of the swelling gel to be determined as it evolves in time, using the formulation of Part 1 to find the local polymer fraction. We discuss the boundary conditions to be applied at the edges of a gel, both on the bulk elastic stress and on the pervadic (pore) pressure in the interstices. Similarities between the equation for the displacements and the equations of classical plate theory are investigated by considering a model problem of a slender cylinder with its base immersed in water drying by evaporation into the surrounding air. In this problem, there is differential drying along the axis of the cylinder, as the base remains swollen while the top dries. The results of our displacement formulation agree qualitatively with experiments we have conducted and provide a physical interpretation of the forced biharmonic equation describing the displacement field.

So far, diesel particulate filters (DPFs) have been widely used to collect diesel particulates including soot in the exhaust after-treatment. However, as the soot is continuously collected in the porous filter, the exhaust pressure (pressure drop) increases. To optimize the filter design for reducing its pressure drop, we need a numerical simulation. In this study, we simulated the particle-laden flow across the DPF. Structure of SiC-DPF was obtained by an X-ray CT technique. We conducted the numerical simulation by changing the soot aggregation diameter (simply called soot size), and evaluated the time-variation of the pressure drop. For discussing the soot deposition process, the contributions of the Brownian diffusion and the interception effect were separately estimated. Especially, we focused on the soot deposition region which could affect the pressure drop, together with the soot cake permeability and the soot packing density. Results show that, as the soot size is smaller, more soot is trapped. As a result, the shift from the depth filtration to the surface filtration is observed earlier. Therefore, for discussing the pressure drop, it is important to consider where the soot deposition occurs as well as the deposited soot mass in the filter.

This paper investigates the combined effects of radiant heat, local Nusselt number and Skin friction coefficient on a channel flow of third grade fluid in the presence of saturated porous medium. It is assumed that the fluid has temperature-dependent variable viscosity and thermal conductivity. The non-linear governing differential equations are obtained and tackled numerically using Spectral element technique and C++ programming language. Increase in the values of radiation parameter and third grade material parameter consequently increase the local Nusselt number and skin friction coefficient. Graphical results showing the effects of various physical parameters are presented and discussed quantitatively. It is concluded that Williamson’s fluid parameter served as a cooling factor in diverse improved technological processes in order to avoid different machines from overheating and enhance their efficiencies.

International audience; Spectral induced polarization (SIP) has the potential for monitoring reactive processes in the subsurface. While strong SIP responses have been measured in response to calcite precipitation, their origin and mechanism remain debated. Here we present a novel geo-electrical millifluidic setup designed to observe microscale reactive transport processes while performing SIP measurements. We induced calcite precipitation by injecting two reactive solutions into a porous medium, which led to highly localized precipitates at the mixing interface. Strikingly, the amplitude of the SIP response increased by 340% during the last 7% increase in precipitate volume. Furthermore, while the peak frequency in SIP response varied spatially over 1 order of magnitude, the crystal size range was similar along the front, contradicting assumptions in the classical grain polarization model. We argue that the SIP response of calcite precipitation in such mixing fronts is governed by Maxwell-Wagner polarization due to the establishment of a precipitate wall. Numerical simulations of the electric field suggested that spatial variation in peak frequency was related to the macroscopic shape of the front. These findings provide new insights into the SIP response of calcite precipitation and highlight the potential of geoelectrical millifluidics for understanding and modeling electrical signatures of reactive transport processes.

Hypothesis Imbibition of a fluid into a porous material involves the invasion of a wetting fluid in the pore space through piston-like displacement, film and corner flow, snap-off and pore bypassing. These processes have been studied extensively in two-dimensional (2D) porous systems; however, their relevance to three-dimensional (3D) natural porous media is poorly understood. Here, we investigate these pore-scale processes in a natural rock sample using time-resolved 3D (i.e., four-dimensional or 4D) X-ray imaging. Experiments We performed a capillary-controlled drainage-imbibition experiment on an initially brine-saturated carbonate rock sample. The sample was imaged continuously during imbibition using 4D X-ray imaging to visualize and analyze fluid displacement and snap-off processes at the pore-scale. Findings We discover a new type of snap-off that occurs in pores, resulting in the entrapment of a small portion of the non-wetting phase in pore corners. This contrasts with previously-observed snap-off in throats which traps the non-wetting phase in pore centers. We relate the new type of pore-snap-off to the pinning of fluid-fluid interfaces at rough surfaces, creating contact angles close to 90°. Subsequently, we provide correlations for displacement events as a function of pore-throat geometry. Our findings indicate that having a small throat does not necessarily favor snap-off: the key criterion is the throat radius in relation to the pore radius involved in a displacement event, captured by the aspect ratio.

In this study, the effects of swirling flow and porous media of triple coaxial ports inverse diffusion flame (TCP-IDF) on the flame shape, temperature and gas emissions are studied. In addition, a comparison between swirling and non-swirling TCP-IDF burner conducted using 5° air swirler. On the other hand, the effect of using a porous screen with 2 mm and 1 mm mesh size including 65°, 45° and 15° flow divergence diffuser on the flame radial and centerline temperatures, and emissions investigated. During all experiments, the air to fuel ratio was constant at 27. The results showed that using swirl reduce CO and UHC emissions and increase the peak temperature and NOx emissions of TCP-IDF. Also increasing the flow divergence angle, all of the CO, UHC, peak temperature and NOx emission decreasing. Concerning the increase in mesh size, it has been noticed that as the mesh size increased, NOx emissions increased while the CO, UHC and peak temperature decreased. Moreover, the combination between the swirl and 65° flow divergence diffuser recorded the lowest value of the CO and UHC emissions. While the combination between the swirl burner with 65° flow divergence diffuser and 1 mm porous screen produced the lowest peak temperature and NOx emissions.

Capillary forces result in the trapping of the oleic phase in porous media even after extensive flushing with brine. Alkali-surfactant-polymer formulations drastically diminish capillary forces, whereas adding polymer to the water phase increases viscous forces, resulting in highly efficient extraction of the residual oil. However, by virtue of its scale, the above process requires a large quantity of chemicals, which poses a threat to the environment. Here, we demonstrate that replacing the polymer with a gas such as nitrogen, flue gas, or carbon dioxide achieves equally superior oil extraction efficiency when using a much smaller amount of chemicals. Mobilized oil is first displaced as a continuous phase (oil-bank) and then as an oil-in-water dispersion. Microflow visualization experiments reveal that dispersed oil spreads at the gas–liquid interface (surfactant solutions) due to the presence of adsorbed surfactant molecules. Our dry-cleaning extraction of hydrocarbons has a wide spectrum of applications and is particularly useful for the production of hydrocarbons from underground formations while mitigating the impact of chemicals on the environment.

Understanding the evolution of solute concentration gradients underpins the prediction of porous media processes limited by mass transfer. Here, we present the development of a mathematical model that describes the dissolution of spherical bubbles in two-dimensional regular pore networks. The model is solved numerically for lattices with up to 169 bubbles by evaluating the role of pore network connectivity, vacant lattice sites and the initial bubble size distribution. In dense lattices, diffusive shielding prolongs the average dissolution time of the lattice, and the strength of the phenomenon depends on the network connectivity. The extension of the final dissolution time relative to the unbounded (bulk) case follows the power-law function, $${B^k/\ell }$$ B k / ℓ , where the constant $$\ell$$ ℓ is the inter-bubble spacing, B is the number of bubbles, and the exponent k depends on the network connectivity. The solute concentration field is both the consequence and a factor affecting bubble dissolution or growth. The geometry of the pore network perturbs the inward propagation of the dissolution front and can generate vacant sites within the bubble lattice. This effect is enhanced by increasing the lattice size and decreasing the network connectivity, yielding strongly nonuniform solute concentration fields. Sparse bubble lattices experience decreased collective effects, but they feature a more complex evolution, because the solute concentration field is nonuniform from the outset.

We present a quantitative bibliometric study of flow battery technology from the first zinc-bromine cells in the 1870’s to megawatt vanadium RFB installations in the 2020’s. We emphasize, that the cost advantage of RFBs in multi-hour charge-discharge cycles is compromised by the inferior energy efficiency of these systems, and that there are limits on the efficiency improvement due to internal cross-over and the cost of power (at low current densities) and due to acceptable pressure drop (at high current densities). Differences between lithium-ion and vanadium redox flow batteries (VRFBs) are discussed from the end-user perspective. We conclude, that the area-specific resistance, cross-over current and durability of contemporaneous VRFBs are appropriate for commercialization in multi-hour stationary energy storage markets, and the most import direction in the VRFB development today is the reduction of stack materials and manufacturing costs. Chromium-iron RFBs should be given a renewed attention, since it seems to be the most promising durable low-energy-cost chemistry.

We present experiments and theory relating to transpiration through unrestrained hydrogel beads in contact with a water reservoir below and air above. Experimentally, we find that saturated hydrogel beads shrink until a steady state is reached in which water flows continuously through the beads. The size of the bead in steady state is sensitive to the evaporation rate, which depends on the relative humidity and speed of the surrounding air, and to the pressure head imposed by the fluid reservoir. Specifically, the bead size decreases with increasing pressure head or evaporation rate. Our one-dimensional model proposes that transport in the hydrogel is driven by gradients in osmotic pressure, caused by gradients in polymer concentration in the hydrogel that correspond to gradients in swelling. If the evaporation rate or the pressure head changes, the adjustment of this gradient requires the bead to change shape and size. Smaller beads have larger gradients of osmotic pressure, which drive higher transpiration rates and can draw water against larger pressure heads.

We study the upscaling of pore-scale solute transport in partially saturated porous media at different saturation degrees. The interaction between structural heterogeneity, phases distribution and small-scale flow dynamics induces complex flow patterns and broad probability distributions of flow, which control key aspects of transport, such as residence and arrival times, dispersion, and spatial solute distributions, as well as chemical reactions. A continuous-time random walk (CTRW) framework that integrates the processes of advection, diffusion, and trapping in immobile zones is used to upscale and evaluate the transport of diluted solutes. Results of this model were compared to direct numerical simulations solving the advection-diffusion equation in experimental saturation patterns. The comparison between simulations results, with different Péclet numbers (Pe), and the physics-based upscaled CTRW approach allows for a quantitative analysis of the governing factors of transport in partially saturated porous media. This analysis shows that the fluid phase saturation decreases the advective tortuosity, the media's characteristic length, the fraction of the immobile region, and the mean trapping time. At the same time, for a given saturation degree, the normalized mean trapping time is proportional to the Pe. This suggests that the characteristic trapping length is proportional to the media's characteristic (correlation) length. Moreover, the trapping frequency decreases with increasing Pe., Water Resources Research, 59 (2), ISSN:0043-1397, ISSN:1944-7973

Heart arrhythmia is caused by abnormal electrical conduction through the myocardium, which in some cases, can be treated with heat. One of the challenges is to reduce temperature peaks—by still guaranteeing an efficient treatment where desired—to avoid any healthy tissue damage or any electrical issues within the device employed. A solution might be employing pulsed heat, in which thermal dose is given to the tissue with a variation in time. In this work, pulsed heat is used to modulate induced temperature fields during radiofrequency cardiac ablation. A three-dimensional model of the myocardium, catheter and blood flow is developed. Porous media, heat conduction and Navier–Stokes equations are, respectively, employed for each of the investigated domains. For the electric field, solved via Laplace equation, it is assumed that the electrode is at a fixed voltage. Pulsed heating effects are considered with a cosine time-variable pulsed function for the fixed voltage by constraining the product between this variable and time. Different dimensionless frequencies are considered and applied for different blood flow velocity and sustained voltages. Results are presented for different pulsed conditions to establish if a reasonable ablation zone, known from the obtained temperature profiles, can be obtained without any undesired temperature peaks.

The efect of groundwater level on forced convection heat transfer from a cylinder of 1 m in diameter buried at a depth of 10 m is studied numerically. The porosity and permeability of the soil are fxed at 0.5 and 1.0× 10–11 m2 , respectively, throughout the present study, while the inlet velocity U0 and the position of the phreatic surface (h), measured from the center of the cylinder, are varied in the ranges from 10–9 to 10–3 m s −1 and from − 4 to 4 m, respectively. Under these conditions, the heat fuxes on the cylinder are computed numerically. Various approximate solutions are also proposed and compared with those obtained numerically. The heat transfer results are also presented in nondimensional form for generality. The paper is divided into three parts, depending on the relative positions of the phreatic surface to the heated cylinder. First, the heat transfer rates are analyzed when the phreatic surface is above the cylinder, so that the cylinder is completely submerged in the water. In the second case, the phreatic surface is assumed to lie below the cylinder, so that the cylinder is left in the water-free space. In the third case, the phreatic surface is in contact with the cylinder surface, so that the cylinder is partially submerged in groundwater. For the above respective cases, three diferent approximate analyses are presented, and their validities and limitations are evaluated in comparison with the numerical calculations.

Contamination caused by nonaqueous phase liquids (or NAPLs) is of great concern in ground water as NAPLs are ubiquitous and persistent pollutants, remaining recalcitrant to bioremediation due to low solubility and limited bioavailability. Chemotaxis, the directed movement of bacteria upon sensing chemical gradients, may facilitate remediation of NAPLs by transporting hydrocarbon-degrading bacteria to residual contamination trapped within the soil matrix. This dissertation work aimed to investigate the role of chemotaxis on bacterial transport in polluted porous media by using a combination of microscopic imaging, microfluidics, mathematical modeling and computer simulation. Naphthalene, one of the sixteen High Priority Pollutants designated by the Environment Protection Agency, was used as a model pollutant that is a chemoattractant for naphthalene-degrading Pseudomonas putida G7. Bacterial chemotactic response was studied across different length scales from a sand column (10e-1 m) to a single pore (10e-4 m). Bacterial transport in a sand column interspersed with discrete NAPL ganglia was modeled using a modified convection-dispersion equation. Computer simulation of the model equation revealed hotspots of bacteria near NAPL ganglia due to chemotactic response and sorption at oil surfaces. Then bacterial transport in pores near NAPL ganglia was observed directly in a dual-permeability microfluidic device and elevated densities of bacteria were found in micropockets near NAPL sources. Simulation results at the pore scale indicated that bacterial distributions were strongly regulated by chemical gradients, which was accounted for in the macroscale model with an increased the bacterial dispersion coefficient by 50%. The transport mechanism in chemotactic bacteria was explored further in a micromodel with similar design, but different pore sizes and bacteria suspensions were introduced in varying fluid velocities. Experiments showed that fluid flow promoted chemotaxis in longer and shorter micropockets at pore velocities lower than 15 m/d and 11 m/d, respectively. The optimal fluid velocity depended on pore dimension and bacterial response time scale, which was further validated by using experimental data from previous literature. Lastly, the influence of fluid flow on bacterial motility and chemotaxis in a single-pore microfluidic chip was examined. We found that bacterial motility and chemotaxis were hampered as fluid velocity increased, which resulted in an adjustment of chemotactic sensitivity coefficient to different extents at varying fluid velocity in continuum modeling. Results of this dissertation work suggested that chemotactic bacteria were more efficient than nonchemotactic bacteria in navigating among pore network in the presence of NAPL contaminants and it was possible to create preferable conditions to aid chemotaxis. Our experiments indicated chemotaxis may overcome the limited bioavailability of NAPLs trapped in low hydraulic permeable strata, and our models provided insight into the impact of chemotaxis on bacterial transport in porous media with the presence of fluid flow.

Our study investigates interplays between dissolution, precipitation, and transport processes taking place across randomly heterogeneous conductivity domains and the ensuing spatial distribution of preferential pathways. We do so by relying on a collection of computational analyses of reactive transport performed in two-dimensional systems where the (natural) logarithm of conductivity is characterized by various degrees of spatial heterogeneity. Our results document that precipitation and dissolution jointly take place in the system, with the latter mainly occurring along preferential flow paths associated with the conductivity field and the former being observed at locations close to and clearly separated from these. High conductivity values associated with the preferential flow paths tend to further increase in time, giving rise to a self-sustained feedback between transport and reaction processes. The clear separation between regions where dissolution or precipitation takes place is imprinted onto the sample distributions of conductivity which tend to become visibly left skewed with time (with the appearance of a bimodal behavior at some times). The link between conductivity changes and reaction-driven processes promotes the emergence of non-Fickian effective transport features. The latter can be captured through a continuous-time random-walk model where solute travel times are approximated with a truncated power law probability distribution. The parameters of such a model shift towards values associated with increasingly high non-Fickian effective transport behavior as time progresses.

The measured accuracy of a heat flux instrument was developed by using the black body of porous media. The SUS 304 stainless wire mesh having PPI (Pores per inch) of 100 and thickness of 0.202 mm constructed by 2 wire-mesh screens was used as the porous media. Three models of a black body of porous media with varying the baking temperature ( T H ), namely 400, 600 and, 800 °C, were modified at the baking period ( t H ) of 8 h. As heat sources, four 150 W infrared lamps were used and vertically placed on the instrument’s top. Five levels of electrical voltages (E), including 50, 100, 150, 200, and 250 V, were tested. The instrument’s measured the distance from the infrared lamp (S) was maintained constant at 25 cm. From the experimental results, the radiative heat flux ( q E x p ) was estimated and then were compared to the reliable instrument manufactured by Hukseflux Thermal Sensors ( q H u k ). In order to evaluate the accuracy of the proposed meter, relative error ( E R e l ) was reported. Emissivity coefficient ( ɛ ) following to the T H , i.e., 400, 600, and 800 °C yielded 0.87, 0.95, and 0.94, respectively. The q E x p gave good agreement to q H u k at T H of 600 °C and the measurement time ( t M ) of over 40 s in all experimental ranges of E.

I use a mechanical model of a soft body to study the dynamics of an individual fluid droplet in a random, non-wettable porous medium. The model of droplet relies on the spring–mass system with pressure. I run hundreds of independent simulations. I average droplets trajectories and calculate the averaged tortuosity of the porous domain. Results show that porous media tortuosity increases with decreasing porosity, similar to single-phase fluid study, but the form of this relationship is different. Supplementary Information The online version contains supplementary material available at 10.1007/s11242-021-01705-z.

The diffusivity equation is a partial differential equation (PDE) which can be used for fluid flow modeling in porous media. Determining reservoir parameters from pressure data (i.e., pressure transient analysis) is one of the most important steps in the process of field development. This initial evaluation can be used to make decisions about future developments. Wireline Formation Testing (WFT) is one of the most popular techniques for parameter estimation and has received significant attention in recent years. The main problem plaguing WFT is a phenomenon known as the “supercharging effect,” which essentially refers to mud invasion, and this, in turn, alters pressure distribution across the system. In this study, an analytical solution for fluid flow modeling in spherical coordinates with non-uniform initial pressure is presented. This new procedure takes into account the effect of mud invasion, or, in other words, the supercharging effect. The accuracy of this derivation was validated using previous semi-analytical solutions (the Laplace method) in addition to field data. New type curves and dimensionless parameters, which can be used for pressure transient analysis, are also proposed. This procedure is applied to the WFT data that was obtained from an oil field in the south of Iran, and an excellent agreement (less than 10% error) was observed. In addition, there is considerable uncertainty regarding the radius of investigation for spherical flow. This is important as this parameter greatly affects the applicability of WFT. The analytical derivation of this study was used to determine a reasonable value for this parameter as well.

An exploration of the unsteady MHD boundary layer flow over a moving vertical porous surface with nanofluids under the influence of a uniform transverse magnetic field and heat radiation absorption effects has been brought out. Two different kinds of water-based nanofluids comprising of Al2O3 and TiO2 are adopted into deliberation. The governing equations for the flow are solved by making use of the Laplace transform method, and the solutions are displayed in closed form. The velocity, temperature, concentration, the shear stress, the rate of heat and mass transportations near the surface has been described graphically for numerous values of the relevant parameters. The velocity and temperature enhances with increasing radiation absorption parameter. It is also observed that an increase of volume fraction of nanoparticles leads to the enhancement of the temperature on central line of the flow. Nusselt number might be tracked down to be elevated for alumina than titanium dioxide nanofluid. The present investigation originated applications in aerospace engineering as well as industrial many mechanisms.

Viscoelastic flow instability, which is compelled by elastic effects rather than inertia, can be driven to a chaotic state termed elastic turbulence (ET) manifested as strong velocity fluctuations with an algebraic decay in the frequency spectrum and increased mixing. We report the first spatiotemporally complete description of ET by considering a broad volume within a novel three-dimensional ordered porous medium, reconstructing flow at a micrometre characteristic length scale ( $\text {Reynolds numbers} \ll 1$ ) via time-resolved microtomographic particle image velocimetry. Beyond a critical Weissenberg number of 2, we observe an elastic flow instability accompanied by an enhanced pressure drop with spectral characteristics typical of ET. Polymer chains in the ET flow state are advected along increasingly curved streamlines between pores such that they accumulate strain and generate a local flow instability evaluated per an established instability criterion based on local evaluation of elastic tensile stress and streamline curvature. The onset of ET leads to increased pore-scale resistance and positive feedback on upstream streamline curvature. ET is thus characterized by a continuous evolution between states of laminar and unstable flow: pores with unstable flow flood their adjacent peers and thus encourage straightened streamlines and flow stability across the array, while positive feedback from flow resistance on streamline curvature results in the instability propagating upstream along the array. By employing a geometrically ordered medium, we permit flow state communication between pores, yielding generalized insights highlighting the significance of spatial correlation and flow history, and thus provide new avenues for explaining the mechanisms of ET.

The dynamics of blood flow in the smallest vessels and passages of the human body, where the cellular character of blood becomes prominent, plays a dominant role in the transport and exchange of solutes. Recent studies have revealed that the micro-haemodynamics of a vascular network is underpinned by its interconnected structure, and certain structural alterations such as capillary dilation and blockage can substantially change blood flow patterns. However, for extravascular media with disordered microstructure (e.g., the porous intervillous space in the placenta), it remains unclear how the medium’s structure affects the haemodynamics. Here, we simulate cellular blood flow in simple models of canonical porous media representative of extravascular biological tissue, with corroborative microfluidic experiments performed for validation purposes. For the media considered here, we observe three main effects: first, the relative apparent viscosity of blood increases with the structural disorder of the medium; second, the presence of red blood cells (RBCs) dynamically alters the flow distribution in the medium; third, increased structural disorder of the medium can promote a more homogeneous distribution of RBCs. Our findings contribute to a better understanding of the cellscale haemodynamics that mediates the relationship linking the function of certain biological tissues to their microstructure.

This study tries to present the auxiliary application of artificial intelligence (AI) in the CFD modeling. In a specific case study, the Cu/water nanofluid flow in a heated porous pipe is considered. The governing equations of the case study are solved by the finite volume method (FVM) of the CFD. The CFD simulations are implemented for different inlet velocities of 0.6, 0.7, 0.9, and 1 m/s. The mixing and turbulent flow of the nanofluid are made by the porous media. So, the eddy viscosity could be an important parameter for prediction in this case study. The bee algorithm based fuzzy interface system (BAFIS) is adopted for the first time, to find the pattern of the eddy viscosity data. In addition, the sensitivity tests are made for achieving the proper values of the number of bees, the percentage recruited bees, and the neighborhood radius. The results highlighted that the bee number, the percentages of bees, and the neighborhood radius are 15, 0.6, and 0.7 respectively for the BAFIS intelligence.

To study the influences of sand and gravel layer and groundwater velocity of Yufuhe River on atrazine migration, adsorption-desorption and sand column experiments were carried out. Results show that the adsorption capacity of montmorillonite, raw sand and washed sand to atrazine sequentially weakens. In different media, the time for atrazine concentrations to peak in washed sand with montmorillonite (WSM), raw sand and washed sand is 60, 135 and 105 minutes respectively, and the peak concentration accounts for 84, 90 and 95% of the initial concentrations. Under different flow rates, the peak time in washed sand at flow rates of 100, 150 and 200 mL/min is 135, 105 and 75 minutes, and the peak time in WSM is 90, 60 and 45 minutes, respectively. Results from this study indicate that increasing flow velocity and suspended colloids concentrations can promote the migration of atrazine in aquifers, while the presence of clay minerals in sand and gravel layers can reduce atrazine migration. Thus, during Yellow River water recharging, the sand and gravel layer of Yufuhe River is helpful to protect the aquifer, but the colloids-associated migration of atrazine can contaminate groundwater in underlying karst aquifer. HIGHLIGHTS Migrations of atrazine in porous media are related to clay minerals and colloids.; Sand and gravel layer can retard the atrazine migration during managed aquifer recharge (MAR).; Increasing groundwater velocity would accelerate atrazine migration.; This study is significant to maintain the long-term operation of the MAR.

Unlike the power-law model, the Ellis model describes the apparent viscosity of a shear-thinning fluid with no singularity in the limit of a vanishingly small shear stress. In particular, this model matches the Newtonian behaviour when the shear stresses are very small. The emergence of the Rayleigh-B\'enard instability is studied when a horizontal pressure gradient, yielding a basic throughflow, is prescribed in a horizontal porous layer. The threshold conditions for the linear instability of this system are obtained both analytically and numerically. In the case of a negligible flow rate, the onset of the instability occurs for the same parametric conditions reported in the literature for a Newtonian fluid saturating a porous medium. On the other hand, when high flow rates are considered, a negligibly small temperature difference imposed across the horizontal boundaries is sufficient to trigger the convective instability., Comment: 13 pages, 5 figures, 2 tables

We explore and develop a Proper Orthogonal Decomposition (POD)-based deflation method for the solution of ill-conditioned linear systems, appearing in simulations of two-phase flow through highly heterogeneous porous media. We accelerate the convergence of a Preconditioned Conjugate Gradient (PCG) method achieving speed-ups of factors up to five. The up-front extra computational cost of the proposed method depends on the number of deflation vectors. The POD-based deflation method is tested for a particular problem and linear solver; nevertheless, it can be applied to various transient problems, and combined with multiple solvers, e.g., Krylov subspace and multigrid methods.

This experimental study is an attempt to apply the constriction size concept for determination of hydraulic conductivity of filter material. Five shapes of granular filter material of different gradations were used for the experimental investigations. The controlling constriction size for selected shapes and gradations were worked out and related to the experimental values of hydraulic conductivity. The empirical model for determination of hydraulic conductivity based on controlling constriction size for each shape of granular filter material was developed. Finally, a combined empirical model for the determination of hydraulic conductivity of granular filters was developed based on shape parameters and the controlling constriction size. The model was validated with the experimental data of a past research work; the predicted values of hydraulic conductivity were found in close approximation to the values obtained from the literature. Results of the present work will help in improving the existing design criteria of protective filters, which form an integral part of the safety of hydraulic structures. HIGHLIGHTS Inclusion of constriction size and shape parameters in the hydraulic conductivity determination of granular filters.; Improvement of the effectiveness of the filter design based on permeability.; Enhancement of water resources management in the essential hydraulic structure design where filters form a critical component.

Research on the scientific and engineering problems of porous media has drawn increasing attention in recent years. Digital core analysis technology has been rapidly developed in many fields, such as hydrocarbon exploration and development, hydrology, medicine, materials and subsurface geofluids. In summary, science and engineering research in porous media is a complex problem involving multiple fields. In order to encourage communication and collaboration in porous media research using digital core technology in different industries, the 5th International Conference on Digital Core Analysis & the Workshop on Multiscale Numerical and Experimental Approaches for Multiphysics Problems in Porous Media was held in Qingdao from April 18 to 20, 2021. The workshop was jointly organized by the China InterPore Chapter, the Research Center of Multiphase Flow in Porous Media at the China University of Petroleum (East China) and the University of Aberdeen with financial support from the National Sciences Foundation of China and the British Council. Due to the current pandemic, a hybrid meeting was held (participants in China met in Qingdao, while other participants joined the meeting online), attracting more than 150 participants from around the world, and the latest multi-scale simulation and experimental methods to study multi-field coupling problems in complex porous media were presented. Cited as: Yang, Y., Zhou, Y., Blunt, M. J., Yao, J., Cai, J. Advances in multiscale numerical and experimental approaches for multiphysics problems in porous media. Advances in Geo-Energy Research, 2021, 5(3): 233-238, doi: 10.46690/ager.2021.03.01

This article describes the incompressible two-dimensional heat and mass transfer of an electrically conducting second-grade fluid flow in a porous medium with Hall and ion slip effects, diffusion thermal effects, and radiation absorption effects. It is assumed that the fluid is a gray, absorbing–emitting but non-scattering medium and the Rosseland approximation is used to describe the radiative heat flux in the energy equation. It is assumed that the liquid is opaque and absorbs and emits radiation in a manner that does not result in scattering. It is considered an unsteady laminar MHD convective rotating flow of heat-producing or absorbing second-grade fluid across a semi-infinite vertical moving permeable surface. The profiles of velocity components, temperature distribution, and concentration are studied to apply the regular perturbation technique. These profiles are shown as graphs for various fluid and geometric parameters such as Hall and ion slip parameters, radiation absorption, diffusion thermo, Prandtl number, Schmidt number, and chemical reaction rate. On the other hand, the skin friction coefficient and the Nusselt number are determined by numerical evaluation and provided in tables. These tables are then analysed and debated for various values of the flow parameters that regulate it. It may be deduced that an increase in the parameters of radiation absorption, Hall, and ion slip over the fluid region increases the velocity produced. The resulting momentum continually grows to a very high level, with contributions from the thermal and solutal buoyancy forces. The temperature distribution may be more concentrated by raising both the heat source parameter and the quantity of radiation. When one of the parameters for the chemical reaction is increased, the whole fluid area will experience a fall in concentration. Skin friction may be decreased by manipulating the rotation parameter, but the Hall effect and ion slip effect can worsen it. When the parameter for the chemical reaction increases, there is a concomitant rise in the mass transfer rate.

In the present paper, the investigation was focused on the physical characterization and determination of porosity for an ion exchange catalyst called Amberlyst-35, which produces environmentally benign gasoline using 3D network modeling (3DNM). In addition, the effect of the different pore size distributions (PSD) has been investigated in porous media (PM). First, the mercury porosimetry (MPo) experiment was carried out to determine the porosity of the Amberlyst-35. Second, the KALINET program was run by Compact Visual Fortran (CVF) and Graphical Input/Output (GINO) for modeling porous structures. Then, the SECTION program was used for different porous 3D random images. The theoretical penetration curve was drawn using data obtained from the KALINET program and fitted to the experimental penetration values of Amberlyst-35 by changing the number of pores in each pressure interval of the PSD. The PSD was a 3D network model size of (N) = 30x30x30, 40x40x40, 50x50x50, which included 83,700-196,800-382,500 pores, respectively. On the other hand, various sections of the 3D stochastic images of the pore network were obtained from the SECTION program. Finally, 3D network images were drawn by the KALINET3D computer program. The MPo method has been applied using computer programs (with desktop computers). Moreover, it was found that the same results were obtained for both the theoretical and experimental data of MPo.

Due to its insulating and draining role, assessing ground vegetation cover properties is important for high-resolution hydrological modeling of permafrost regions. In this study, morphological and effective hydraulic properties of Western Siberian Lowland ground vegetation samples (lichens, Sphagnum mosses, peat) are numerically studied based on tomography scans. Porosity is estimated through a void voxels counting algorithm, showing the existence of representative elementary volumes (REVs) of porosity for most samples. Then, two methods are used to estimate hydraulic conductivity depending on the sample's homogeneity. For homogeneous samples, direct numerical simulations of a single-phase flow are performed, leading to a definition of hydraulic conductivity related to a REV, which is larger than those obtained for porosity. For heterogeneous samples, no adequate REV may be defined. To bypass this issue, a pore network representation is created from computerized scans. Morphological and hydraulic properties are then estimated through this simplified representation. Both methods converged on similar results for porosity. Some discrepancies are observed for a specific surface area. Hydraulic conductivity fluctuates by 2 orders of magnitude, depending on the method used. Porosity values are in line with previous values found in the literature, showing that arctic cryptogamic cover can be considered an open and well-connected porous medium (over 99 % of overall porosity is open porosity). Meanwhile, digitally estimated hydraulic conductivity is higher compared to previously obtained results based on field and laboratory experiments. However, the uncertainty is less than in experimental studies available in the literature. Therefore, biological and sampling artifacts are predominant over numerical biases. This could be related to compressibility effects occurring during field or laboratory measurements. These numerical methods lay a solid foundation for interpreting the homogeneity of any type of sample and processing some quantitative properties' assessment, either with image processing or with a pore network model. The main observed limitation is the input data quality (e.g., the tomographic scans' resolution) and its pre-processing scheme. Thus, some supplementary studies are compulsory for assessing syn-sampling and syn-measurement perturbations in experimentally estimated, effective hydraulic properties of such a biological porous medium.

Funder: Shell; doi: http://dx.doi.org/10.13039/100004378, Single-phase fluid flow velocity maps in Ketton and Estaillades carbonate rock core plugs are computed at a pore scale, using the lattice Boltzmann method (LBM) simulations performed directly on three-dimensional (3D) X-ray micro-computed tomography (µCT) images (≤ 7 µm spatial resolution) of the core plugs. The simulations are then benchmarked on a voxel-by-voxel and pore-by-pore basis to quantitative, 3D spatially resolved magnetic resonance imaging (MRI) flow velocity maps, acquired at 35 µm isotropic spatial resolution for flow of water through the same rock samples. Co-registration of the 3D experimental and simulated velocity maps and coarse-graining of the simulation to the same resolution as the experimental data allowed the data to be directly compared. First, the results are demonstrated for Ketton limestone rock, for which good qualitative and quantitative agreement was found between the simulated and experimental velocity maps. The flow-carrying microstructural features in Ketton rock are mostly larger than the spatial resolution of the µCT images, so that the segmented images are an adequate representation of the pore space. Second, the flow data are presented for Estaillades limestone, which presents a more heterogeneous case with microstructural features below the spatial resolution of the µCT images. Still, many of the complex flow patterns were qualitatively reproduced by the LBM simulation in this rock, although in some pores, noticeable differences between the LBM and MRI velocity maps were observed. It was shown that 80% of the flow (fractional summed z-velocities within pores) in the Estaillades rock sample is carried by just 10% of the number of macropores, which is an indication of the high structural heterogeneity of the rock; in the more homogeneous Ketton rock, 50% of the flow is carried by 10% of the macropores. By analysing the 3D MRI velocity map, it was found that approximately one-third of the total flow rate through the Estaillades rock is carried by microporosity—a porosity that is not captured at the spatial resolution of the µCT image.

Wetting films can develop in the corners of angular pores under strong wetting conditions. Modeling the dynamics of corner film remains elusive using direct numerical simulations because of the significant scale difference between main meniscus and corner film flow. In this paper, the modified interacting capillary bundle model (ICB), developed in our previous work to describe accurately corner film dynamics in a single square tube, is incorporated into a single-pressure dynamic pore network model (DPNM) to simulate imbibition in strongly wetting porous media with corner film flow. The traditional pore network is decomposed into several layers of interacting subpore networks where the 0th layer of subpore network simulates the main meniscus flow and higher layers the corner film flow. The fluid flow between different layers is captured by interlayer throats. In addition, the snap-off mechanism caused by the thickening of wetting corner film is considered. The accuracy of the developed model is validated for four cases: spontaneous imbibition in a single square tube, wetting fluid redistribution through corner films under a capillary pressure difference, snap off in a narrow throat connecting two large pores, and imbibition dynamics in a real microfluidic porous geometry. The validated model is then used to simulate both spontaneous and controlled imbibition in a pore network with random pore size distribution. The interaction between corner film and main meniscus flow in porous media is analyzed from a pore-scale perspective. ISSN:0043-1397 ISSN:1944-7973

Unmanned Aerial vehicles are nowadays involved in a wide range of applications, such as surveillance, safety control, scientific research, and commercial activities. The logistics industry, in particular, is showing a substantial interest in a partial transition of the last-mile delivery service from ground to air transport. A key point to make this scenario feasible resides in the design of delivery hubs to serve the surrounding areas, thus overcoming the logistical difficulties of a door-to-door delivery while respecting the strict regulations in terms of noise. The proposed paper deals with the study and design of an urban hub for package delivery that uses natural elements such as hedges to limit the noise footprint associated with drone operations by exploiting the shielding capabilities of natural barriers. Some constraints driving the design are identified, leading to a tentative conceptual design. The acoustic property of a sample hedge is evaluated using an equivalent porous medium approach, informed by parameters estimated by image processing of the external surface of the hedge. Eventually, the model is used in coupled BEM-FEM simulations of simplified designs. Preliminary results show encouraging noise reductions in the areas surrounding the hub.

The paper is concerned with the effect of angle of attack on the interaction noise between a turbulent flow and a NACA 0012 airfoil. This experimental study considers an airfoil with a porous leading edge up to 10% of the chord and compares the noise levels to a solid airfoil leading edge at a Reynolds number of Re=2.5x10^5. Turbulence is generated by the means of a passive grid and the direct noise measurements are performed using a microphone array. The airfoil is instrumented for both steady and unsteady wall pressure measurements. The Cp distribution over the surface of the airfoil is considered up to large geometric angles of attack for both the solid and porous leading edge cases. From far-field noise measurement, it is found that radiated sound is reduced at small geometric angles of attack at low frequencies for the porous airfoil. At higher angles of attack the Cp distribution of the porous leading edge case appears to be similar with that of a stalled airfoil, suggesting porous leading edges at higher angles of attack stall earlier than a solid airfoil.

Spontaneous imbibition plays a significant role in different technical applications, and several analytical models have been proposed for predicting the fluid imbibition mass into porous media based on the fractal theory. Herein, these previous models are reconsidered in view of the obvious difference between the effective porosity and the areal porosity of porous media. Firstly, an implicit equation for fractal tortuosity is proposed and a modified correlation for the areal porosity is presented; then, a semi-analytical prediction model for fluid imbibition mass with gravity pressure is derived; finally, comparisons of predictions among several previous models with the present model are carried out. The modeling results show consistency with the experimental data published in the literature. Cited as: Li, Y., Yu, D., Niu, B. Prediction of spontaneous imbibition in fractal porous media based on modified porosity correlation. Capillarity, 2021, 4(1): 13-22, doi: 10.46690/capi.2021.01.02

The main cable of suspension bridges is subject to corrosion and requires advanced anti-corrosion technology. Consequently, the internal airflow of the main cable has become a significant research focus. This study employs image processing and machine learning to analyze the cross-sectional images of the main cable and reveals the distribution characteristics of pores and fractures within the main cable cross-section. The numerical simulation model of the main cable is divided into inner and outer parts based on porosity, with porosity levels of 18.16% and 32.11%, respectively. Fractures randomly occurred in the inner part, with a probability of 31.37%. A simulation model based on fractured porous media (FPM) is developed, which innovatively incorporates the fracture flow model into the numerical simulation of the internal airflow of the main cable. The numerical simulation clearly explores the intricate details of the internal flow field of the main cable, revealing that the existence of fractures has a great impact on the internal flow field of the main cable. Additionally, the relative deviation of specific frictional head loss between the field experiment and numerical simulation is about 6.83%, indicating that the numerical simulation results are relatively reliable.

The simultaneous estimation of coefficients and the initial conditions for model fractional parabolic systems of porous media is reduced to the minimization of a least-squares cost functional. This inverse problem uses information about the pressures at a finite number of space time points. The Frechet gradient of the cost functional is derived. The application of the conjugate gradient method for numerical parameter estimation is also discussed. Computational results with noise-free and noisy data illustrate the efficiency and accuracy of the proposed algorithm.

Manganese (Mn) could adversely affect water quality and is a concern for drinking water safety. In contrast to Mn-contaminated groundwater systems, Mn concentrations can increase up to 2 orders of magnitude in low background level groundwater systems (Mn < 100 µg/L). It is interesting to explore related hydrogeological and hydrochemical processes and controlling mechanisms. Our data showed that Mn of groundwater from Quaternary porous aquifers in the Changping region of Beijing in China varied from 0.02 to 522 µg/L, with an average of 45 µg/L. The high Mn concentration (>100 µg/L) in groundwater occurred in the lower plain, while the low Mn concentration was distributed in the upper plain. Association was not obvious between the Mn concentration and the depth of the groundwater. The water–rock interaction (e.g., dissolution of Mn-bearing minerals) and redox reactions dominated the distribution of Mn in groundwater. Particularly, the reduction of Mn4+ was a major cause of increasing Mn2+ concentration in groundwater. This is further evidenced by declining dissolved oxygen (DO) and NO3 in groundwater from the upper plain to the lower plain part. This study contributes to further understandings of hydrochemical processes for the enrichment of Mn in groundwater and offers a reference for the management and oversight of groundwater containing an excessive Mn level.

An isothermal piston is a device that can achieve near-isothermal compression by enhancing the heat transfer area with a porous media. However, flow resistance between the porous media and the liquid is introduced, which cannot be neglected at a high operational speed. Thus, the influence of rotational speed on the isothermal piston compression system is analyzed in this study. A flow resistance mathematical model is established based on the face-centered cubic structure hypothesis. The energy conservation rate and efficiency of the isothermal piston are defined. The effect of rotational speed on resistance is discussed, and a comprehensive energy conservation performance assessment of the isothermal piston is analyzed. The results show that the increasing rate of the resistance work increases significantly proportional to the rotational speed, and the proportion of resistance work in the total work increases gradually and sharply. The total work including compression and resistance cannot be larger than the compression work under adiabatic conditions. The maximum rotational speed is 650 rpm.