Search Results (36)

The efficiency of an electrolyzer is significantly influenced by mass, heat, and charge transport within its porous transport layer (PTL). The infeasibility of measuring them in-situ makes it challenging to study their influence experimentally, leading to the adoption of various modeling approaches. This study applies pore network (PN) modeling to investigate mass transport properties and capillary invasion behavior in three commercial titanium felt PTLs commonly used in proton exchange membrane water electrolyzers (PEMWEs). One PTL has a graded structure. Reconstructed PNs were derived from microcomputed X-ray tomography (µ-CT) data, allowing for a detailed analysis of pore size distributions, absolute and relative permeabilities, capillary pressure curves, and residual liquid saturations. The results from the PN approach are compared to literature correlations. The absolute permeability of all PTLs is between 1.1 × 10⁻¹⁰ m² and 1.5 × 10⁻¹⁰ m², with good agreement between PNM results and predictions from the Jackson and James model and the Tomadakis and Sotirchos model, the two latter involving the fiber diameter as a model parameter. The graded PTL, with fiber diameters varying between 25 µm and 40 µm, showed the best agreement with literature correlations. However, the capillary pressure curves exhibited significant deviations from the Leverett and Brooks–Corey equations at low and high liquid saturations, emphasizing the limitations of these correlations. In addition, residual liquid saturation varied strongly with PTL structure. The thicker PTL with a slightly narrower pore size distribution, demonstrated a lower residual liquid saturation (19%) and a more homogeneous invasion compared to the graded PTL (64%), which exhibited significant gas fingering. The results suggest that higher gas saturation could enhance gas removal, with much higher relative permeabilities, despite the greater PTL thickness. In contrast, the graded PTL achieves the highest relative liquid permeability (~70%) while maintaining a relative gas permeability of ~30%. These findings highlight the impact of microstructure on invasion and transport properties and suggest PN modeling as a powerful tool for their study. Full article

We compared the applicability of 3D fibrous scaffolds, produced by our patented centrifugal spinning technology, in soft tissue engineering. The scaffolds were prepared from four different biocompatible and biodegradable thermoplastics, namely, polylactide (PLA), polycaprolactone (PCL), poly(3-hydroxybutyrate) (PHB), and poly(1,4-butylene succinate) (PBS) and their blends. The combined results of SEM and BET analyses revealed an internal hierarchically organized porosity of the polymeric micro/nanofibers. Both nanoporosity and capillary effect are crucial for the water retention capacity of scaffolds designed for tissue engineering. The increased surface area provided by nanoporosity enhances water retention, while the capillary effect facilitates the movement of water and nutrients within the scaffolds. When the scaffolds were seeded with adipose-derived stem cells (ASCs), the ingrowth of these cells was the deepest in the PLA/PCL 13.5/4 (w/w) composite scaffolds. This result is consistent with the relatively large pore size in the fibrous networks, the high internal porosity, and the large specific surface area found in these scaffolds, which may therefore be best suited as a component of adipose tissue substitutes that could reduce postoperative tissue atrophy. Adipose tissue constructs produced in this way could be used in the future instead of conventional fat grafts, for example, in breast reconstruction following cancer ablation. Full article

The super-sized pore-throat network model can reflect both microscopic pore characteristics and macroscopic heterogeneity and is excellent in describing cross-scale flow fields. At present, there is no algorithm that can generate a micro pore-throat network model at a macro reservoir scale. This study examines algorithms for super-sized pore-throat network reconstruction using actual core sample data. It conducts a random simulation of mineral growth and dissolution under the constraints of four microscopic pore structure parameters: porosity, coordination number, pore radius, and throat radius. This approach achieves high-precision, super-sized, and regional pore-throat network modeling. Comparative analysis shows that these four parameters effectively guide the random growth process of super-sized pore-throat networks. The overall similarity between the generated pore-throat network model and real core samples is 88.7% on average. In addition, the algorithm can partition and control the generation of pore-throat networks according to sedimentary facies. The 100-megapixel model with 85,000 pores was generated in 455.9 s. This method can generate cross-scale models and provides a basis for cross-scale modeling in physical simulation experiments and numerical simulations. Full article

Volcanic rock reservoirs for oil and gas are known worldwide for their considerable heterogeneity. Micropores and fractures play vital roles in the storage and transportation of natural gas. Samples from volcanic reservoirs in Songliao Basin, CS1 and W21, belonging to the Changling fault depression and the Wangfu fault depression, respectively, have similar lithology. This study employs micro–nano CT scanning technology to systematically identify the key parameters and transport capacities of natural gas within volcanic reservoirs. Using Avizo 2020.1software, a 3D digital representation of rock core was reconstructed to model pore distribution, connectivity, pore–throat networks, and fractures. These models are then analyzed to evaluate pore/throat structures and fractures alongside microscopic parameters. The relationship between micropore–throat structure parameters and permeability was investigated by microscale gas flow simulations and Pearson correlation analyses. The results showed that the CS1 sample significantly exceeded the W21 sample in terms of pore connectivity and permeability, with connected pore volume, throat count, and specific surface area being more than double that of the W21 sample. Pore–throat parameters are decisive for natural gas storage and transport. Additionally, based on seepage simulation and the pore–throat model, the specific influence of pore–throat structure parameters on permeability in volcanic reservoirs was quantified. In areas with well–developed fractures, gas seepage pathways mainly follow fractures, significantly improving gas flow efficiency. In areas with fewer fractures, throat radius has the most significant impact on permeability, followed by pore radius and throat length. Full article

The detailed characterization of the pore structure in sandstone is pivotal for the assessment of reservoir properties and the efficiency of oil and gas exploration. Traditional fully supervised learning algorithms are limited in performance enhancement and require a substantial amount of accurately annotated data, which can be challenging to obtain. To address this, we introduce a semi-supervised framework with a U-Net backbone network. Our dataset was curated from 295 two-dimensional CT grayscale images, selected at intervals from nine 4 mm sandstone core samples. To augment the dataset, we employed StyleGAN2-ADA to generate a large number of images with a style akin to real sandstone images. This approach allowed us to generate pseudo-labels through semi-supervised learning, with only a small subset of the data being annotated. The accuracy of these pseudo-labels was validated using ensemble learning methods. The experimental results demonstrated a pixel accuracy of 0.9993, with a pore volume discrepancy of just 0.0035 compared to the actual annotated data. Furthermore, by reconstructing the three-dimensional pore structure of the sandstone, we have shown that the synthetic three-dimensional pores can effectively approximate the throat length distribution of the real sandstone pores and exhibit high precision in simulating throat shapes. Full article

Coalbed methane represents a promising source of clean and efficient unconventional energy. The intricate network of micro–nano pores within coal serves as the primary adsorption space for gas, contributing to the complexity of gas migration channels. In this study, based on the box-counting method, three coal samples representing low, medium, and high ranks were subjected to high-precision micro-CT scanning and nano-CT scanning to generate three-dimensional (3D) pore network models using Avizo visualization software. This facilitated the accurate and quantitative characterization of the micro–nano pore structures within coal reservoirs. The results indicated that the face rate distribution range of each sample was large, indicating relatively strong heterogeneity in each sample. The volume fractal dimension of each sample, determined through micro–nano-CT scanning, was around 2.5, while the surface fractal dimension exhibited oscillatory characteristics with moderate uniformity. The pore equivalent radius and throat equivalent radius distributions were unimodal across all the samples, with the micro-CT scanning revealing a concentration primarily within the range of 100–400 μm for the pore equivalent radius and within 200 μm for the throat equivalent radius. Conversely, the nano-CT scanning exhibited concentrations primarily within the range of 500–2500 nm for the pore equivalent radius and within 2000 nm for the throat equivalent radius. The analysis of the 3D reconstruction structures indicated that the middle-rank coal exhibited more developed large–medium pores compared with the low-rank and high-rank coal, while the low-rank and high-rank coal exhibited relatively more micro–small pores. Furthermore, the low-rank coal exhibited the fewest number of pores but the largest average pore equivalent radius and throat radius. Additionally, the middle–high-rank coal exhibited a relatively larger number of pores. Despite the complex topological structures observed in each sample, a significant proportion indicated a coordination number of 0–20, indicating excellent connectivity within the coal samples. This study is conducive to the optimization of coalbed methane surface development blocks and the formulation of reasonable development plans. Full article

Ultralow-temperature fluids (such as liquid nitrogen, liquid CO₂) are novel waterless fracturing technologies designed for dry, water-sensitive reservoirs. Due to their ultralow temperatures, high compression ratios, strong frost heaving forces, and low viscosities, they offer a solution for enhancing the fracturing and permeability of low-permeability reservoirs. In this study, we focus on the combined effects of high-pressure fluid rock breaking, low-temperature freeze-thaw fracturing, and liquid-gas phase transformation expansion on coal-rock in low-permeability reservoirs during liquid nitrogen fracturing (LNF). We systematically analyze the factors that limit the LNF effectiveness, and we discuss the pore fracture process induced by low-temperature fracturing in coal-rock and its impact on the permeability. Based on this analysis, we propose a model and flow for fracturing low-permeability reservoirs with low-temperature fluids. The analysis suggests that the Leidenfrost effect and phase change after ultralow-temperature fluids enter the coal support the theoretical feasibility of high-pressure fluid rock breaking. The thermal impact and temperature exchange rate between the fluid and coal determine the temperature difference gradient, which directly affects the mismatch deformation and fracture development scale of different coal-rock structures. The low-temperature phase change coupling fracturing of ultralow-temperature fluids is the key to the formation of reservoir fracture networks. The coal-rock components, natural fissures, temperature difference gradients, and number of cycles are the key factors in low-temperature fracturing. In contrast to those in conventional hydraulic fracturing, the propagation and interaction of fractures under low-temperature conditions involve multifield coupling and synergistic temperature, fluid flow, fracture development, and stress distribution processes. The key factors determining the feasibility of the large-scale application of ultralow-temperature fluid fracturing in the future are the reconstruction of fracture networks and the enhancement of the permeability response in low-permeability reservoirs. Based on these considerations, we propose a model and process for LNF in low-permeability reservoirs. The research findings presented herein provide theoretical insights and practical guidance for understanding waterless fracturing mechanisms in deep reservoirs. Full article

The drive for sustainable energy solutions has spurred interest in solid oxide fuel cells (SOFCs). This study investigates the impact of sintering temperature on SOFC anode microstructures using advanced 3D focused ion beam–scanning electron microscopy (FIB-SEM). The anode’s ceramic–metal composition significantly influences electrochemical performance, making optimization crucial. Comparing cells sintered at different temperatures reveals that a lower sintering temperature enhances yttria-stabilized zirconia (YSZ) and nickel distribution, volume, and particle size, along with the triple-phase boundary (TPB) interface. Three-dimensional reconstructions illustrate that the cell sintered at a lower temperature exhibits a well-defined pore network, leading to increased TPB density. Hydrogen flow simulations demonstrate comparable permeability for both cells. Electrochemical characterization confirms the superior performance of the cell sintered at the lower temperature, displaying higher power density and lower total cell resistance. This FIB-SEM methodology provides precise insights into the microstructure–performance relationship, eliminating the need for hypothetical structures and enhancing our understanding of SOFC behavior under different fabrication conditions. Full article

Green mining is an effective way to achieve sustainable development in the coal industry. Preventing coal and gas outburst dynamic disasters are essential for ensuring sustainable and safe mining. The numerous microscopic pores within the coal serve as the primary storage space for gas, making it critical to explore the structural distribution and seepage characteristics to reveal the disaster mechanism. Under mining stress, gas within the micropores of the coal migrates outward through cracks, with these cracks exerting a significant control effect on gas migration. Therefore, this study focuses on utilizing natural fractured coal bodies as research objects, employing a micro-CT imaging system to conduct scanning tests and digital core technology to reconstruct sample pore and fracture structures in three dimensions, and characterizing the pores, cracks, skeleton structure, and connectivity. A representative elementary volume (REV) containing macro cracks was selected to establish an equivalent model of the pore network, and a seepage simulation analysis was performed using the visualization software. Revealing the seepage characteristics of fractured coal mass from a microscopic perspective. The research results can provide guidance for gas drainage and dynamic disaster early warning in deep coal mines, thus facilitating the sustainable development of coal mining enterprises. Full article

In this study, alumina ceramics with hierarchical pores were successfully fabricated using freeze casting. Experimental studies show that both the solid loading of the slurry and the thermal insulation layer at the interface of the slurry and cooling plate can influence the pore characteristics of cast samples. In order to examine the pore characteristics and evaluate the permeability of the freeze-cast samples fabricated under different conditions, a generative adversarial network (GAN) method was employed to reconstruct the three-dimensional (3D) microstructure from two-dimensional (2D) scanning electron microscopy (SEM) images of the samples. Furthermore, GAN 3D reconstruction was validated against X-ray tomography 3D reconstruction results. Based on the GAN reconstructed microstructures, the permeability and pore distribution of the various samples were analyzed. The sample cast with 35 wt.% solid loading shows an optimal permeability. Full article

Membrane emulsification technology has garnered increasing interest in emulsion preparation due to controllable droplet size, narrower droplet size distribution, low energy consumption, simple process design and excellent reproducibility. Nevertheless, the pore structure and surface engineering in membrane materials design play a crucial role in achieving high-quality emulsions with high throughput simultaneously. In this work, an oriented interpenetrating capillary network composed of highly aligned and interconnected wood cell lumens has been utilized to fabricate an emulsion membrane. A novel honeycomb porous ZnO layer obtained by a seed prefabrication–hydrothermal growth method was designed to reconstruct wood channel surfaces for enhanced microfluid mixing. The results show that through the unique capillary mesh microstructure of wood, the emulsion droplets were smaller in size, had narrower pore-size distribution, and were easy to obtain under high throughput conditions. Meanwhile, a well-designed ZnO layer could further improve the emulsion quality of a wood membrane, while the emulsifying throughput is still maintained at a higher level. This demonstrates that the convection process of the microfluid in these wood capillary channels was intensified markedly. This study not only develops advanced membrane materials in emulsion preparation, but also introduces a brand-new field for functional applications of wood. Full article

The tissue engineering field is currently advancing towards minimally invasive procedures to reconstruct soft tissue defects. In this regard, injectable hydrogels are viewed as excellent scaffold candidates to support and promote the growth of encapsulated cells. Cross-linked gelatin methacryloyl (GelMA) gels have received substantial attention due to their extracellular matrix-mimicking properties. In particular, GelMA microgels were recently identified as interesting scaffold materials since the pores in between the microgel particles allow good cell movement and nutrient diffusion. The current work reports on a novel microgel preparation procedure in which a bulk GelMA hydrogel is ground into powder particles. These particles can be easily transformed into a microgel by swelling them in a suitable solvent. The rheological properties of the microgel are independent of the particle size and remain stable at body temperature, with only a minor reversible reduction in elastic modulus correlated to the unfolding of physical cross-links at elevated temperatures. Salts reduce the elastic modulus of the microgel network due to a deswelling of the particles, in addition to triple helix denaturation. The microgels are suited for clinical use, as proven by their excellent cytocompatibility. The latter is confirmed by the superior proliferation of encapsulated adipose tissue-derived stem cells in the microgel compared to the bulk hydrogel. Moreover, microgels made from the smallest particles are easily injected through a 20G needle, allowing a minimally invasive delivery. Hence, the current work reveals that powdered cross-linked GelMA is an excellent candidate to serve as an injectable hydrogel for adipose tissue engineering. Full article

Spontaneous combustion coal gangue (SCCG) is considered to be an aluminosilicate-based solid waste containing various toxic ions. The alkali-activation method for this material can not only fully use its potential hydration activity but also solidify the hazardous components to some extent. Through introducing additional Pb²⁺, the solidification behavior of heavy metal Pb²⁺ for an SCCG-based geopolymer was studied in the present paper. The solidification efficiencies were evaluated by Pb²⁺ leaching rates under neutral and acidic conditions, while its mechanism was explained by the methods of XRD, TG, FT-IR, SEM, and MIP. The results show that the Pb²⁺ solidification efficiency increases along with the curing age, and acidic rather than neutral conditions lead to a more intensive solidification capacity. Judging by the permissive maximum value of 5 mg/L, the Pb²⁺ original concentrations under neutral and acidic circumstances should be lower at 2.0 wt.% and 3.0 wt.%, respectively. The Pb²⁺ absorption is dominated by the physical process, due to the formation of no new hydration products. However, the Pb²⁺ addition would interrupt the reconstruction of the Si-Al network structure, slowing the accumulation of N-A-S-H gel and the densifying of the matrix. When the Pb²⁺ concentration grows, the sizes of hydration productions shrink continuously, more defects appear in the microstructure of the geopolymer, and the pore structure deteriorates rapidly, all of which accelerate the diffusion of toxic ions to the external condition. Full article

Archaeocyaths are a group of extinct filter feeders that flourished in the early Cambrian period and occupied an important position in the evolution of basal fauna and the early marine ecosystem. However, the detailed morphological and anatomical information of this group are still unclear due to insufficient fossil material and limited experimental analyses. Here, we report exquisitely preserved phosphatized archaeocyathan fossil cups, ca. 515 million years old, from the top of the Shuijingtuo Formation (Series 2, Stage 3) and the Xiannüdong Formation (Series 2, Stage 3) of the Yangtze Platform, South China. Detailed observation of their external morphology via scanning electron microscopy (SEM) and micro-computed tomography (Micro-CT) analysis revealed detailed information of their internal structure. They have a typical double-walled cup, with the perforated inner and outer walls concentrically distributed, but the structure between the two walls differs. The inverted cone-shaped cups have radially distributed septa between the walls. Perforated septa connect the two walls. The low and columnar cups have canals between the two walls, forming the network. These pores and cavities constitute an important component of the water current system (pumping and filtering water with a network of canals and chambers) and influence the process of filtration in the cup. In comparison to traditional thin-section analysis, the combination of SEM and Micro-CT analysis on phosphatized archaeocyaths presented in this study further explored the detailed internal structure and finely reconstructed the microscopic overall morphology and anatomy, which provide important information to help us understand the systematic taxonomy, anatomy, and morphology of archaeocyaths during the Cambrian period. Full article

To investigate the void mesostructure in porous asphalt mixtures (PA), computed tomography (CT) and Avizo were utilized to scan and reconstruct the three-dimensional (3D) void model of PA-16 specimens. The void mesostructure of the specimen was quantitatively characterized through the anisotropy evaluation index. The equivalent pore network model (PNM) was extracted using the medial axis method. Based on the PNM model, the topological structure of the specimen and the morphological characteristics of the connected pores were analyzed. The results showed that the void anisotropy evaluation method can reflect the microscopic morphology of voids in porous asphalt mixtures. The cross-sectional porosity of representative elementary volume (REV) is mainly distributed between 20% and 25%, and about 90% of the macropores have a diameter between 0.5 mm and 3 mm. The distribution of cross-sectional porosity is uneven along the REV height direction. As the smallest cross-section of the seepage path, the equivalent radius of the throat is mainly between 0.1 mm and 1.5 mm, which is much smaller than the equivalent radius of the pore. The topological structure of pores is quite different, and their coordination numbers are mainly concentrated within 18. The pores with coordination numbers 1 to 10 constitute the main body of the pores inside REV, accounting for over 98% of the total number of pores. In addition, the permeability calculation results show that there is a significant difference in the permeability of each axis of REV compared to the total permeability of the superpave gyratory compactor (SGC) specimen, which illustrates that the permeability distribution presents an obvious spatial anisotropy. This study effectively reveals the heterogeneity of the 3D void morphology of porous asphalt mixtures, and it provides a reference for a better understanding of the void flow rules in drainage pavements. Full article