Reduction Of Effective Porosity Research Articles

New insights into the parameterization of the dry surface layer and its hydrogeochemical mechanism: An experimental study

Knowledge of the parameterization of the dry surface layer (DSL) is essential for evaluating near-surface water flow and water balance in arid and semi-arid areas. Existing studies have parameterized DSL thickness and vapor flow as functions of the soil moisture content (SMC) in the surface layer to predict soil evaporation. However, hydrochemical processes related to DSL development have been ignored, including changes in hydrochemistry, the underlying hydrochemical mechanism, and the role of dissolved substances in the DSL development. Herein, we performed a series of soil evaporation experiments for 260 days and explored the factors influencing DSL development (e.g., soil texture, atmospheric temperature, SMC, solutes). Evaporation experiments were performed using silty loess, sandy loess, and fine sand with a 60-cm water table. Results showed that the cumulative evaporation of silty loess, sandy loess, and fine sand over the experimental period were 1,391.52, 460.10, and 185.53 mm, respectively, which determined by the maximum height of liquid flow continuity. The content of total dissolved solids (TDS) and major ions at the surface soil were significantly higher than the values at deep depths of 5‒55 cm, which largely depend on evaporative water loss. Evolutionary trends of chemical facies in sand media along the liquid water migration were from HCO3-Ca type to SO4·Cl-Na type. This was attributed to mineral dissolution at a depth of 5–55 cm and their transport with liquid water, resulting in the precipitation of salt crystals at the surface soil. Furthermore, a consolidated DSL with a thickness of 3.0–3.5 cm in the sandy loess and a loose DSL with a thickness of 1.5–2.0 cm in fine sand were observed at the end of the experiments. The accumulation of solutes at the surface leads to a reduction in effective porosity and the aggregation of soil particles during continuous drying, which facilitates the consolidation of DSL in sandy loess. This overestimated the DSL thickness, resulting in a difference between the experimental and predicted evaporation rates by Fick's law. Overall, these results highlight the limitations of considering DSL thickness as a function of SMC only, providing new insights into hydrochemical processes and dissolved solutes involving DSL parameterization during continuous soil drying.

Experimental study of the impact of CO2 injection on the pore structure of coal: A case study from the Bowen Basin, Australia

This study investigates the impact of carbon dioxide (CO2) on the pore structure of coal during CO2 injection to understand the technical challenges associated with CO2 sequestration in depleted coal seam gas reservoirs. In an integrated approach, Micro-Computed Tomography (micro-CT) scanning, helium porosity and air permeability tests are performed on a coal sample prior to and after CO2 flooding experiments to identify both reversible and irreversible changes in cleat and fracture networks. The results indicate that irreversible changes contribute to a 43% reduction in effective porosity, which can be readily observed in the 3D model of the cleat and fracture networks constructed after CO2 flooding. At lower effective stresses, pore compressibility offsets the matrix swelling effect, resulting in improved permeability, which is beneficial for CO2 injection. Additionally, the analysis of borehole image logs of the study well reveals that most fractures and cleats terminate within coal intervals, with very few fractures extending into adjacent strata that are siltstone and fine sandstone with very low permeability.

Fabrication and in vitro investigation of hyperbranched poly-lysine-grafted warp knitted polypropylene sling for potential treatment of stress urinary incontinence.

Polypropylene (PP) sling implantation is the most commonly performed procedure for women with stress urinary incontinence (SUI). However, concerns have arisen regarding complications caused by slings, including the common issue of erosion, which can be attributed to various factors such as the body's response and bacterial contamination. To address these concerns, we have developed a rectangular mesh self-locking edge sling with a large pore size and lightweight design. Promising results have been obtained from preliminary in vivo mechanical reliability tests, including uniaxial tensile tests. In comparative in vitro fixed load tensile tests and simulated Tension-free Vaginal Tape (TVT) and Transobturator Vaginal Tape inside-out (TVT-O) technique tests using commercial slings, our sling demonstrated less transverse wrinkling. Both slings achieved an effective porosity of over 45% under the TVT technique. However, the commercial sling experienced a significant reduction in effective porosity during the TVT-O technique, whereas our sling maintained a stable effective porosity with minimal wrinkling. Furthermore, we successfully developed cationic hydration rejection-driven antibacterial-anti-fouling coatings on the surface of our sling by grafting hyperbranched poly-lysine (HBPL) mediated by polynorepinephrine. The HBPL coating imparts a positive charge and hydrophilicity to the sling, resulting in elevated bactericidal activity and reducing protein adhesion. An optimal grafting concentration of 20 mg mL-1 was selected, confirming the stability and biocompatibility of the sling coating. This coating is expected to reduce the likelihood of postoperative erosion. Overall, our research represents significant advancements in improving the safety and performance of PP slings for stress urinary incontinence, potentially leading to a reduction in complications following surgery.

Elastic mesh with thermoplastic polyurethane filaments preserves effective porosity of textile implants.

In hernia surgery, meshes with small pores tend to be filled by fibrous tissue, which reduces their stretchability and causes patient complaints. Because of the inelasticity of current meshes, mechanical strain might cause pores to collapse even in large-pore mesh constructions. In this study, a mesh with elastic thermoplastic polyurethane (TPU) filaments was constructed to prevent pore size changes even under mechanical strain, and its biocompatibility in comparison with polyvinylidene fluoride (PVDF) was evaluated. A mesh was constructed using PVDF with elastic TPU filaments and mechanically tested. After midline laparotomy in 20 rabbits, we placed a 15 cm × 3 cm mesh as inlay in the defect. Animals were randomized to either the TPU or PVDF group. After 7 or 21 days, mesh expansion was measured under pneumoperitoneum, and abdominal walls were explanted for immunohistochemical investigations. In vitro, TPU meshes showed a slight reduction in effective porosity from 46% at tension-free conditions to 26% under longitudinal and to 34% under transverse strain. The nonelastic PVDF meshes showed a marked reduction in effective porosity from 70% to 7% and 52%, respectively. The TPU mesh had a breaking elongation of 101% and a tensile strength of 35 N/cm. In vivo, both meshes achieved healing of the incision without hernial defect. The TPU mesh maintained its elasticity under pneumoperitoneum. The amount of CD68-positive, Ki67-positive, and apoptotic cells was significantly lower in the TPU group after 7 and 21 days. The newly developed TPU mesh shows elasticity, structural stability, and preserved effective porosity under mechanical strain. Immunohistochemistry indicates superior biocompatibility of TPU mesh compared with PVDF after 7 and 21 days.

Effect of residual oil saturation on hydrodynamic properties of porous media

To understand the effect of residual oil on hydraulic properties and solute dispersive behavior of porous media, miscible displacement column experiments were conducted using two petroleum products (diesel and engine oil) and a sandy soil. The effective water permeability, effective water-filled porosity, and dispersivity were investigated in two-fluid systems of water and oil as a function of residual oil saturation (ROS). At the end of each experiment, the distribution of ending ROS along the sand column was determined by the method of petroleum ether extraction-ultraviolet spectrophotometry. Darcy’s Law was used to determine permeability, while breakthrough curves (BTCs) of a tracer, Cl−, were used to calibrate effective porosity and dispersivity. The experimental results indicate that the maximum saturated zone residual saturation of diesel and engine oil in this study are 16.0% and 45.7%, respectively. Cl− is found to have no sorption on the solid matrix. Generated BTCs are sigmoid in shape with no evidence of tailing. The effective porosity of sand is inversely proportional to ROS. For the same level of ROS, the magnitude of reduction in effective porosity by diesel is close to that by engine oil. The relative permeability of sand to water saturation decreases with increasing amount of trapped oil, and the slope of the relative permeability–saturation curve for water is larger at higher water saturations, indicating that oil first occupies larger pores, which have the most contribution to the conductivity of the water. In addition, the reduction rate of relative permeability by diesel is greater than that by engine oil. The dispersivity increases with increasing ROS, suggesting that the blockage of pore spaces by immobile oil globules may enhance local velocity variations and increase the tortuosity of aqueous-phase flow paths.

Characteristics of subsurface wastewater infiltration systems fed with dissolved or particulate organic matter

The influent type of organic matter (dissolved or particulate) on the characteristics of two subsurface wastewater infiltration systems (SWISs) was investigated. One of the SWISs was fed with dissolved organic matter (glucose, assumed to be readily biodegradable) and the other with particulate organic matter (starch, assumed to be slowly biodegradable). Results showed that both biofilm growth and particle accumulation in substrate could reduce the effective porosity and infiltration rate of SWIS, especially for the high organic matter concentration wastewater. The reduction in effective porosity and infiltration rate was primarily caused by organic particle accumulation. The contribution of the accumulated organic particle to the process of clogging was greater than that of biofilm growth and the clogging mainly occurred in the upper layer in starch-fed systems. The SWISs fed with glucose were not clogged till the end of experiments. The hydraulic retention time (HRT) increased with time in start-up period and was almost invariable after mature in glucose-fed systems; in starch-fed systems, clogging of substrate prolonged the HRT. The two identical experimental SWISs were almost equal efficiencies for the removal of chemical oxygen demand (COD). The removal efficiencies of COD were not influenced by clogging under the experimental conditions. Ammonia N removal efficiency was higher in glucose-fed systems than that in starch-fed systems.

Influence of leachate pollution on mechanical properties of compacted clay: A case study on behaviors and mechanisms

The environmental safety and engineering stability of landfills are always a concern of the public in view of its potential impact on public health. This study investigates the effect of leachate corrosion on the mechanical properties of a compacted clay. Batch tests were conducted to measure the permeability as well as the compressibility and the shear strength of the compacted clay that was polluted by landfill leachate under different concentrations. The influence mechanisms of leachate on the mechanical properties of compacted clay were investigated through microscopic experiments. The results showed that the hydraulic conductivity of compacted clay decreased because of the reduction in effective porosity resulting from the infiltration of leachate. Moreover, hydraulic conductivity decreased with the increase in leachate concentration and penetration time. The increase in leachate concentration respectively led to a decrease in the cohesion (C) and an increase in the internal friction angle (φ) of leachate-polluted compacted clay. The content of quartz and clay minerals in compacted clay decreased while albite increased after pollution. The compressibility of the compacted clay rises with pollution. An increase in compressibility and compressive deformation as well as a reduction in the compression modulus occurred as the leachate concentration increased. The maximum decline of void ratio was 9.7%.

Validated Leverett Approach for Multiphase Flow in PEFC Diffusion Media: II. Compression Effect

This work is the second part of a series of papers to describe the multiphase transport mechanism in thin-film polymer electrolyte fuel cell (PEFC) diffusion media (DM). The present work is devoted to delineating the effects of compression. Direct measurements of drainage capillary pressure-saturation curves for SGL series carbon paper DM tailored with a range of mixed wettability were performed at room temperature under various compressions (0, 0.6, and ) typically encountered in a fuel cell assembly. Based on these benchmark data, an appropriate form of the Leverett approach, including a Leverett-type empirical function that incorporates the effect of compression and the mixed wettability characteristics of the tested DM samples, was developed. The presented approach can determine the capillary pressure as a function of hydrophobic additive content, liquid saturation, compression, and uncompressed porosity of the DM. Compression leads to an increase in capillary pressure, effectively caused by the corresponding reduction in effective porosity. Any increase in hydrophobicity amplifies the compression effect, yielding a higher capillary pressure for the same saturation level. Furthermore, the fraction of connected hydrophilic pores is observed to be reduced with an increase in compression, leading to a favorable reduction in water storage capacity of the fuel cell DM.

The effect of a biofilm on solute diffusion in fractured porous media

At sites in fractured rock where contamination has been exposed to the rock matrix for extended periods of time, the amount of contaminant mass residing in the matrix can be considerable. Even though it may be possible to diminish concentrations by the advection of clean water through the fracture features, back diffusion from mass held in the matrix will lead to a continuing source of contamination. In such an event, the development of a biofilm (a thin film of microbial mass) on the wall of the fractures may act to limit or prevent the back diffusion process. The objective of this preliminary study is to explore the influence imparted by the presence of a biofilm on the process of matrix diffusion. The investigation was conducted using radial diffusion cells constructed from rock core in which biofilm growth was stimulated in a central reservoir. Once biofilms were developed, forward diffusion experiments were conducted in which a conservative solute migrated from the central reservoir into the intact rock sample. Diffusion experiments were performed in a total of 11 diffusion cell pairs where biofilm growth was stimulated in one member of the pair and inhibited in the other. The effect of the presence of a biofilm on tracer diffusion was determined by comparison of the diffusion curves produced by each cell pair. A semi-analytical model that accounts for the presence of a biofilm was used to investigate the effect of the biofilm on mass transfer due to changes in the effective porosity, effective diffusion coefficient, and the depth of penetration of the biofilm into the intact rock. The results show that the biofilm acted to plug the rock matrix, rather than forming a discrete layer on the reservoir surface. The reduction in effective porosity due to the biofilm ranged from 6% to 52% with the majority of the samples in the 30% to 50% range. Based on the present results, with more efficient biofilm stimulation, it is reasonable to assume that a more complete plugging of the microcrack porosity might be possible, leaving a much thicker and efficient barrier than could be achieved via a surface biofilm.

Precipitation sealing and diagenesis: 1. Experimental results

During burial and diagenesis of granular aggregates, significant permeability reduction may be induced by the formation of low‐temperature, authigenic minerals. To quantitatively assess the importance of this process, we have conducted a series of hydrothermal flow‐through experiments using deionized water and labradorite/quartz sand. All experiments were conducted in a modified triaxial apparatus, configured to allow continuous permeability measurements. Under most of the conditions tested, significant permeability reduction is observed with no concurrent decrease in porosity. The overall permeability reduction sometimes exceeds 1 order of magnitude over 4 days and is positively correlated to temperature and deviatoric stress. Scanning electron microscope observations together with data from additional experiments show that the observed permeability reduction is entirely a result of secondary mineral growth. Si and Al concentrations in the postexperiment fluids are also correlated to temperature and stress, confirming the link between the chemical state of the system and permeability behavior. In all experiments, permeability reduction is fastest early and levels off in the late stages. To explain the permeability behavior as a function of time, a conceptual model is developed in which precipitation of authigenic minerals is rapid at early times while dissolution of quartz and labradorite is most active. As the system approaches equilibrium, the components necessary for secondary mineral formation are liberated at a lower rate, thereby causing precipitation to slow. Although authigenic mineral formation does not reduce total pore space in these experiments, there is a reduction in effective porosity, which results in permeability reduction.