Percolation Time Research Articles

Uncovering the impact of morphology of porous media and capillary number on immiscible oil recovery using computational fluid dynamics

Pore-scale simulation and analysis of oil displacement in digital rocks has shown great promise in tracking oil recovery in porous media. This paper examines three digital rocks with varying pore and throat radii but the same porosities, studying their behavior under immiscible oil recovery through waterflooding. Computational fluid dynamics was used to conduct numerical simulations to observe the impact of rock morphology on breakthrough times, residual oil saturations, and oil displacement patterns. The validity of the simulation mechanism is confirmed in both imbibition and drainage conditions through the pore doublet Chatzis' experiment. This study consisted of 33 separate simulations which varied in mobility ratios, interfacial tensions, and injection velocities. The findings suggest that smaller pore and throat radii result in higher oil recovery and water percolation and faster breakthrough times that facilitates the effects of viscous fingering. An increase in capillary number was found to have a significant impact on oil recovery in larger pores and throats.

Swelling inhibition and percolation promotion of PQ-10 on weathered crust elution-deposited rare earth ores

Weathered crust elution-deposited rare earth ores (WREOs) are rich in medium and heavy rare earth. In order to improve the in-situ leaching process, which is prone to landslides and poor permeability, cationic hydroxyethyl cellulose (PQ-10) was used as a novel green swelling inhibitor and percolation promoter and was mixed with conventional leaching agent ammonium sulfate ((NH4)2SO4) to form a composite leaching agent to study the performance and mechanism of swelling inhibition and percolation promotion. Adding PQ-10 can inhibit the hydration swelling of WREOs, promote the percolation effect of the leaching agent, improve the rare earth (RE) leaching efficiency, and reduce the impurity aluminum (Al) leaching efficiency. Compared with the conventional leaching agent 2 wt% (NH4)2SO4, the percolation time is reduced by 50% by using the composite leaching agent (0.02 wt% PQ-10+2 wt% (NH4)2SO4). PQ-10 has positively charged quaternary ammonium groups and hydrophilic group hydroxyl groups, which makes it easy to adsorb on WREOs multiple sites through electrostatic interaction and hydrogen bonding, weakening the electrostatic repulsion between mineral particles, reducing the WREOs interlayer spacing, compressing the double electric layer thickness at the solid-liquid interface, weakening the mineral hydration swelling and increasing the percolation rate. The long carbon chains of the polymer entangle and link the fine mineral particles to agglomerate them, increasing their particle size and reducing their hydration dispersion, and preventing blockage of the percolation pores caused by migration of the fine particles through the ore body with the solution. PQ-10 molecules also insert the mineral interlayer and expulsion of the internal water, further inhibiting the swelling of WREOs. Adding PQ-10 reduces the surface tension of (NH4)2SO4 solution, improving the spreading and spreading ability of the solution, reducing the adhesion work between molecules in the solid-liquid phase and the adhesion work reduction factor. It proves that PQ-10 promotes the percolation effect of the leaching process of WREOs. In addition, PQ-10 expands the leaching pore size and seepage channels, further improving the percolation rate.

PATTERN OF POTASSIUM RELEASE FROM SLOW RELEASE FERTILIZER POTASSIUM CLORIDE-BENTONITE FERTILIZER

Potassium has an important role in the process of plant growth, but its presence and availability in the soil are limited, because potassium is easily lost and flows out by water. Increasing the efficiency of potassium fertilization can be pursued through the formulation of fertilizer in the form of slow-release fertilizer (SRF) using bentonite. This study aimed to determine the release of potassium in potassium chloride fertilizer into the soil after bonding with acid-activated bentonite coated with potassium chloride. The composition of the KCl fertilizer made varies with bentonite with a mass ratio (g) of 1:1; 2:1; 3:1; 4:1; and 5:1, with a percolation time of 28 days. The concentration of released potassium was determined using an atomic absorption spectrophotometer. Material characterization was carried out by FTIR. The results showed that the ratio 1:3 had the highest potassium content of 45.12% with an incubation time of 28 days. The concentration of released potassium on day 7; 14; 21; and 28 respectively (12.55±1.25)%, (28.39±1.49)%, (5.,91±0.98)%, and (70.49±1.36)% . The results of the characterization of the determination of the fungal group on SRF3 were not significantly different from that of activated bentonite. Even though there were differences in the intensity of certain peaks and changed the functional groups.

On the Running Time of Hypergraph Bootstrap Percolation

Given $r\geq2$ and an $r$-uniform hypergraph $F$, the $F$-bootstrap process starts with an $r$-uniform hypergraph $H$ and, in each time step, every hyperedge which "completes" a copy of $F$ is added to $H$. The maximum running time of this process has been recently studied in the case that $r=2$ and $F$ is a complete graph by Bollob\'as, Przykucki, Riordan and Sahasrabudhe [Electron. J. Combin. 24(2) (2017), Paper No. 2.16], Matzke [arXiv:1510.06156v2] and Balogh, Kronenberg, Pokrovskiy and Szab\'o [arXiv:1907.04559v1]. We consider the case that $r\geq3$ and $F$ is the complete $r$-uniform hypergraph on $k$ vertices. Our main results are that the maximum running time is $\Theta\left(n^r\right)$ if $k\geq r+2$ and $\Omega\left(n^{r-1}\right)$ if $k=r+1$. For the case $k=r+1$, we conjecture that our lower bound is optimal up to a constant factor when $r=3$, but suspect that it can be improved by more than a constant factor for large $r$.

Assessing Vulnerability of Regional-Scale Aquifer-Aquitard Systems in East Gulf Coastal Plain of Alabama by Developing Groundwater Flow and Transport Models

Groundwater vulnerability assessment helps subsurface water resources management by providing scientific information for decision-makers. Rigorous, quantitative assessment of groundwater vulnerability usually requires process-based approaches such as groundwater flow and transport modeling, which have seldom been used for large aquifer-aquitard systems due to limited data and high model uncertainty. To quantify the vulnerability of regional-scale aquifer-aquitard systems in the East Gulf Coastal Plain of Alabama, a three-dimensional (3D) steady-state groundwater flow model was developed using MODFLOW, after applying detailed hydrogeologic information to characterize seven main aquifers bounded by aquitards. The velocity field calibrated by observed groundwater heads was then applied to calculate groundwater age and residence time for this 3D aquifer-aquitard system via backward/forward particle tracking. Radioactive isotope data (14C and 36Cl) were used to calibrate the backward particle tracking model. Results showed that shallow groundwater (<300 ft below the groundwater table) in southern Alabama is mainly the Anthropocene age (25–75 years) and hence susceptible to surface contamination, while the deep aquifer-aquitard systems (700 ft or deeper below the groundwater table) contain “fossil” waters and may be safe from modern contamination if there is no artificial recharge/discharge. Variable horizontal and vertical vulnerability maps for southern Alabama aquifer-aquitard systems reflect hydrologic conditions and intermediate-scale aquifer-aquitard architectures in the regional-scale models. These large-scale flow/transport models with coarse resolutions reasonably characterize the broad distribution and vertical fluctuation of groundwater ages, probably due to aquifer-aquitard structures being captured reliably in the geology model. Parameter sensitivity analysis, vadose zone percolation time, wavelet analysis, and a preliminary extension to transient flow were also discussed to support the aquifer vulnerability assessment indexed by groundwater ages for southern Alabama.

Pore-scale parametric sensitivity analysis of liquid water transport in the gas diffusion layer of polymer electrolyte membrane fuel cell

Water management in the gas diffusion layer (GDL) is crucial for improving the performance of polymer electrolyte membrane fuel cells (PEMFCs). In this study, a modified stochastic method that fully took into account the fiber deflection and layered structure in the thickness direction was proposed to reconstruct the realistic porous structures of three-dimensional (3D) GDL. The liquid water transport within the GDL was then numerically studied using the 3D Lattice Boltzmann method (LBM). Subsequently, the contributions of different parameters (porosity, fiber diameter, thickness, wettability, and pressure difference) to the transport process of liquid water were elucidated by implementing a multi-parametric sensitivity analysis (MPSA). The numerical results indicate that the liquid water penetration process can be divided into initial injection, selective percolation, and diffusion stages. With the decreases in porosity or increase in contact angle, the flow is inclined to transform from gentle flow to accumulation and secondary breakthrough owing to the increased percolation resistance. Further accumulation of the liquid within GDL can be identified when the evolution time progresses from the breakthrough point to the creep point. Moreover, for GDL, the degree of influence of the structural parameters on the breakthrough velocity is ranked in the order of GDL porosity, fiber diameter, GDL thickness, pressure difference, and GDL wettability. The total liquid saturation is dominated by GDL wettability and is insensitive to GDL porosity and fiber diameter owing to the conflict between the percolation resistance of the pores and the percolation time within GDL. The current work consolidates the understanding of the influencing mechanisms of different structural parameters on liquid water transport characteristics, contributing to the optimal design of the gas diffusion layer.

Hydraulic conductivity assessment of falling head percolation tests used for the design of on-site wastewater treatment systems

The suitability of a location for an on-site wastewater treatment process (for areas which lack access to centralised wastewater treatment systems) requires an assessment of the permeability of the soil into which the effluent will be discharged. In many jurisdictions this is determined using some type of in-situ percolation test. Falling head percolation tests, which give a value of percolation time (PT) that is empirically related to the notion of hydraulic conductivity, are widely used as they are relatively simple to carry out, but the test does not have a sound theoretical framework and test methods are not standardised internationally. In comparison, the saturated hydraulic conductivity of a soil obtained from a constant head well permeameter test is independent of test conditions, and so is a more suitable metric for design. A database of over 900 falling head tests carried out across a range of different subsoil types in Ireland has been collated, all with the inherent limitations of the existing regulative framework regarding the percolation test and soil texture assessment. These tests were then modelled using Hydrus 2-D numerical modelling simulations to determine equivalent field saturated hydraulic conductivity (Kfs) values and thereby provide a correlation with PT values across the range of subsoil conditions. In addition, falling head tests have been carried out in parallel to constant head permeameter tests in the field and compared against the relationship derived from the broad dataset of simulated results. This revealed an optimal solution by which to determine Kfs from the field permeameter test (using parameters recommended for most structured soils from clays to loams). The trendline based on Irish data was also compared against more generic formulations of the relationship between PT, and Kfs and shown to match closely, particularly the Reynolds (2016) ‘unified’ methodology. Finally, the Irish threshold PT limits for on-site wastewater treatment have been converted to Kfs values and compared against other international standards.

Characterization of the structural build-up of cementitious suspensions containing attapulgite from the perspective of flocculent structure

In this paper, the structural build-up characteristics of cementitious suspensions containing attapulgite were explored from the perspective of flocculent structure. Firstly, the fluidity, rheology, adhesiveness, and segregation resistance of cementitious suspensions containing two kinds of attapulgite (burning followed by grinding (BGA) and grinding followed by burning (GBA)) were investigated. Then the small-amplitude oscillating shear tests were used to examine the structural build-up of cementitious suspension in different time periods. The percolation time (tperc) and the rigidification rate (G'rigid) of the percolated structures were measured. Finally, the bonding strength coefficient (BSC) was used to characterize the flocculent structures’s size and strength, and its relationship with macroscopic experimental parameters and structural build-up characteristic parameters were investigated.The results indicated that GBA and BGA affected the flow expansion, plastic viscosity, yield stress, and adhesiveness of the cementitious suspension by changing the flocculent structures, and the BSC was the key property that determined these parameters. While the bleeding rate was affected by the combined effect of BSC and standing time. GBA and BGA were found to have different effects on the flocculent structures with different standing time periods. The BSC was strongly correlated with G'rigid and tperc, which could characterize the structural build-up of cementitious suspension.

Percolation Time and Rigidification Rate of Cementitious Suspensions

Percolation Time and Rigidification Rate of Cementitious Suspensions

Rheological Characterization of Cementitious Suspensions with Limestone Calcined Clay for Pumping Applications

Pumping of concrete is an efficient placement technique. When the concrete is pumped in a pipe, the lubrication layer (LL) forms and its rheological properties predominantly dictate the flow and govern the resumption operations. The primary purpose of this study was to investigate the effects of a new admixture, limestone calcined clay (LC2) at variable replacements (0%, 5%, 10%, and 20% by weight) on rheological properties of cementitious suspensions (equivalent to lubricating layer). An increase in yield stress, plastic viscosity, structuration rate, and decreased percolation time were observed with increments in the proportion of LC2 in cementitious suspensions. However, at the optimal dosage of superplasticizer, yield stress and plastic viscosity were decreased by 78% and 82%, respectively, even for the maximum replacement (20%) of LC2. Similarly, the percolation time increased by 15% and the structuration rate decreased by 39%, allowing additional time to deal with any pumping operational delays. From the results, it is also evident that higher deformation ratio of the lubrication layer is beneficial for concretes at rest due to pumping interruption. This study contributes to the fundamental understanding of viscoelastic properties of LC2-based cementitious suspensions, which will improve understanding of lubrication layer behavior for pumping operations.

Static and dynamic resilience assessment for sustainable urban transportation systems: A case study of Xi 'an, China

Resilient transportation provides a new perspective for constructing sustainable cities. Although current studies have analyzed transportation resilience from different perspectives, accurately assessing the resilience of urban transport systems remains a significant challenge. This paper proposes a framework to evaluate the static and dynamic resilience of urban transportation systems. Based on systemic thinking and sustainability perspectives, we establish a Bayesian network model that comprehensively considers social, economic, organizational, and technological dimensions to assess the static resilience of urban transportation systems. We adopt percolation theory to determine the minimum required performance (MRP) of road network and explore the spatial distribution of dynamic resilience based on traffic performance under traffic congestion. Results show that the transportation resilience of Xi'an showed a continuous growth trend between 2010 and 2020, from 0.37 to 0.64. In addition, the primary task of enhancing resilience is to improve the system's restorative capacity, adaptive capacity, and resourcefulness. The MRP of the road network is 0.37. The areas with larger resilience loss and percolation time are concentrated along the Second and Third Ring Expressway and in the south and southwest areas. The resilience of the urban center area is more potent. The time of the response process is twice that of the recovery process. The above results could help managers and decision-makers have a comprehensive and clear understanding of the transportation resilience and have practical significance for constructing a sustainable urban transportation system.

Percolation and connection times in multi-scale dynamic networks

We study the effects of mobility on two crucial characteristics in multi-scale dynamic networks: percolation and connection times. Our analysis provides insights into the question, to what extent long-time averages are well-approximated by the expected values of the corresponding quantities, i.e., the percolation and connection probabilities. In particular, we show that in multi-scale models, strong random effects may persist in the limit. Depending on the precise model choice, these may take the form of a spatial birth–death process or a Brownian motion. Despite the variety of structures that appear in the limit, we show that they can be tackled in a common framework with the potential to be applicable more generally in order to identify limits in dynamic spatial network models going beyond the examples considered in the present work.

Impact of hydro-chemical conditions on structural and hydro-mechanical properties of chalk samples during dissolution experiments

The importance of karst reservoirs for water resources, and their complexity in terms of structural properties and hydraulic responses, require a better understanding of the formation and location of conduits in these systems, in particular for chalk reservoirs. For this purpose, we conduct laboratory experiments of acid solutions injection in chalk core samples using a homemade experimental device. Three different flow rates and two acid concentrations are applied on six samples at atmospheric conditions with Peclet numbers ranging from 0.1 to 1.7 and Damköhler numbers from 10−6 to 10−3. Hydraulic and chemical measurements are carried out during the experiments, while petrophysical characterization is conducted on the samples before and after the reactive percolation experiments. The analysis of these data shows an increase in permeability of the rock samples due to calcite dissolution, which is associated with the creation of preferential conduits. We also observe that the initial structural properties control the dissolution regime with the following main conclusions. For homogeneous systems, the overall dissolution rate and percolation time are directly linked to the considered flow rate and injected acid concentration. For heterogeneous systems, (i) pre-existing large-scale structural heterogeneities control the location of newly created paths while reducing the value of the dissolution rate, and (ii) micro-scale heterogeneities result in highly heterogeneous general structures, which are responsible for channels formation while applying low Damköhler numbers.

Influence of coffee brewing methods on the chromatographic and spectroscopic profiles, antioxidant and sensory properties

Cold brewing coffee has gained increasing popularity as a novel brewing method. A completely different flavour profile during cold brewing extraction (smooth and mild) is a result of the low-energy process, prolonged water-grind contact times and long preparation time. The aim of our research was to compare coffee drinks obtained with an innovative device for a faster, dynamic cold coffee extraction process (Hardtank) to drinks prepared traditionally in 24 h and hot brewed drinks. This study investigated the differences in chemical composition (volatile, non-volatile and lipid compounds), sensory properties and antioxidant capacity of coffee drinks from various extraction processes carried out at variable brewing temperatures, times and percolation modes. The results showed that the new cold maceration technique using coffee bed percolation (Hardtank) improved the quality of cold coffee drinks, making them similar in taste to hot coffee drinks. Among the studied extractions, the combination of a lower temperature (19.3 °C) and percolation process appeared to be the ideal setting for the most efficient extraction of compounds such as chlorogenic acids, gallic acid, caffeine, trigonelline, 5-(hydroxymethyl)furfural and lipids and consequently for their intake. In addition, FTIR spectra indicated an even 4 times greater quantity of lipids in Hardtank drinks than in classic cold brew and up to 5 times more lipids than in hot brew coffee, which contribute to the formation of the aroma and flavour. The decreased extraction time and use of coffee bed percolation could be beneficial for the quality and taste of cold brew products.

Pore Network Modeling to Study the Impacts of ‎Geometric Parameters on Water Transport inside Gas ‎Diffusion Layers

A pore network model (PNM) is proposed for the simulation of water transport inside the cathode side ‎gas diffusion layer (GDL) of polymer electrolyte fuel cells (PEFCs) during the transient start-up period as ‎well as the steady state. Numerous two-dimensional random networks representing GDL are generated ‎followed by statistical averaging of the results (Monte Carlo methods) to circumvent the uncertainties ‎imposed by random pore size distributions. The resulting liquid water saturation profiles within GDLs ‎exhibit concave patterns which is typically encountered in capillary fingering flow regimes in porous ‎media. The effect of GDL thickness and current collector rib width as two geometric parameters on water ‎transport dynamics are separately investigated. It turns out that thin and thick GDLs compared to the base ‎case can have contradicting outcomes on the account of total water saturation in the network. On the ‎other hand, wide current collector ribs give rise to liquid water saturation and build-up within GDL which ‎can lead to flooding. At the end, three-dimensional networks are generated demonstrating higher pore ‎connectivity which results in higher percolation times and different invasion patterns.‎

Prediction model for irrigation return flow considering lag effect for arid areas

Irrigation return flow (RF) in arid areas has a significant lag, and current RF prediction models have an inadequate consideration of this. This study proposed the concepts of lag time contour (LTC) and area frequency curve (AFC), both of which can be used for describing the spatial distribution of RF lag time in an arid area. AFC can be determined from LTC or obtained from RF observations and use of the trial-and-error method. A new RF prediction model was developed for arid regions based on LTC and AFC, and the model couples deep percolation (DP) and lag time in order to achieve the prediction of RF. This model was applied in the eastern part of the Jingdian irrigation district in northwest China, and the results indicate that the model predictions fit well with the observations and that the model is reliable. Analysis of DP and RF in the study area between 2000 and 2020 proved that when lag time is not greater than half a year, the main factor that influences yearly-scale RF is DP, and when lag time is greater than one year, the factors that influence yearly-scale RF are DP and lag time. The main influences on monthly-scale RF are DP and lag time, but this is to a lesser extent than their influence on yearly-scale RF. LTC and AFC help understand the process of RF production in arid regions and the influence lag time has on RF. Additionally, the RF prediction model developed for this study is suitable for RF prediction at different time scales, and also for RF predictions in arid areas where there is insufficient hydrogeological data. This is of great significance for the efficient use of water resources in arid regions’ irrigation areas.

The invariant measure of PushASEP with a wall and point-to-line last passage percolation

We consider an interacting particle system on the lattice involving pushing and blocking interactions, called PushASEP, in the presence of a wall at the origin. We show that the invariant measure of this system is equal in distribution to a vector of point-to-line last passage percolation times in a random geometrically distributed environment. The largest co-ordinates in both of these vectors are equal in distribution to the all-time supremum of a non-colliding random walk.

ESTUDO DE MEIO REATIVO PARA BARREIRAS REATIVAS PERMEÁVEIS (BRP): ENSAIOS LABORATORIAIS

Esse manuscrito apresenta resultados de estudos laboratoriais para avaliar a adequabilidade de zeólitas como meio reativo de Barreiras Reativas Permeáveis (BRPs), em 3 faixas granulométricas (4,0x10-4 a 1,0x10-3 m, 1,0x10-3 a 2,0x10-3 m e 1,0x10-3 a 3,0x10-3 m). Estudos foram desenvolvidos por meio da caracterização física, química, mineralógica, permeabilidade e de sorção. A zeólita caracterizada é da espécie Clinoptilolita, com peso específico dos sólidos de 22,87 kN/m3, razão Si/Al de 6,8 e capacidade de troca catiônica de 180 cmolc/kg. Os diferentes arranjos volumétricos das partículas geraram valores de peso específico aparente seco de 10,01 a 11,00 kN/m3 e condutividades hidráulica saturada de 1x10-5 a 3x10-4 m/s, o que compatibiliza os arranjos com diferentes meios geológicos. Em termos de sorção, a isoterma do tipo Langmuir ajusta com r2 de 0,997 e, quanto a cinética de adsorção, o comportamento ocorre por meio do compartilhamento de elétrons entre zeólita e soluto, com coeficientes de reação de primeira ordem variando de 0,06 a 0,4h-1 em função do tempo de percolação. Os resultados mostram que as zeólitas nas faixas granulométricas estudadas são adequadas para uso como meio reativo de BRP em espessuras economicamente viáveis para áreas contaminadas inseridas em materiais geológicos relativos à Formação Botucatu.

Behaviour of Capillary Barrier Covers Subjected to Rainfall with Different Patterns

The behaviour of capillary barrier covers (CBCs) subjected to rainfall has been extensively studied by many researchers. However, the patterns of rainfall are seldom considered in previous studies, and therefore, the behaviour of CBCs subjected to rainfall with different patterns is still unknown. To this end, this study aims to investigate the effect of rainfall patterns on the behaviour and performance of CBCs, and identify the rainfall pattern, under which the performance of the CBC is the worst. Using a newly developed soil column test apparatus, a series of laboratory soil column experiments were conducted. The results indicated that when rainfall duration is short, the patterns of rainfall only affect the volume water content (VWC) and pore water pressure (PWP) significantly at the upper part of the column; when rainfall duration is long, the patterns of rainfall can significantly affect the VWC and PWP throughout the whole column. The percolation and breakthrough time of the CBC were also influenced by rainfall patterns; the advanced rainfall pattern produced the largest percolation, and resulted in the shortest time for CBCs to break through, whereas the delayed rainfall pattern generated the least percolation and resulted in the longest time for CBCs to break through. Based on the percolation and breakthrough time, it seems that the advanced pattern is the worst-case scenario for the CBCs subjected to rainfall. The obtained results not only imply the necessity of rainfall patterns to be involved in the study of the CBCs subjected to rainfall but they also can be helpful for the practical design of the CBCs.

Solid-liquid extraction of cellulases from fungal solid-state cultivation in a packed bed bioreactor

Cellulases are enzymes required for the production of second-generation ethanol (E2G) via biochemical route. The current paper reports the development of an apparatus for solid-liquid extraction of cellulases from solid-state fermentation (SSF) carried out in a packed bed bioreactor (PBB), operated as batch and as semicontinuous. The case study was the cultivation of Myceliophthora thermophila I-1D3b on sugarcane bagasse (SCB) and wheat bran (WB) (7: 3 w/w). The current work integrates the PBB to the first downstream step for recovering the enzymes produced by SSF. The substrate was inoculated and packed into the modules that composed the PBB. The fermentation occurred at 45 °C and air was supplied with flow rate of 350 L/h. At the end of the cultivations, each module was placed in an extraction column, a dynamic closed system in which distilled water was circulated and made to percolate the cultivated material. Variables tested were volume of water per mass of substrate, water flow rate and time of percolation. Higher contact time (120 min) and higher flow rate (2.4m3/h) allowed us to recover up to 85% of total enzyme activity by percolation. Lower volume (20mL/g) provides higher titer extract. The apparatus showed to be promising for SSF downstream, mainly for semicontinuous operation of PPBs.