Search Results (72)

Gas voids inevitably form during the solidification of phase change materials (PCMs) due to volumetric contraction and thus deteriorate the thermal conductivity of solidified PCMs. In this work, the gas void morphology and distribution in solidified pure paraffin within a cubic thermal energy storage unit are experimentally studied. The three-dimensional structure of the solidified pure paraffin is reconstructed via computed tomography (CT) scanning with a resolution of up to 25 µm. Four distinct morphological types of gas voids are found, including irregular elliptical gas voids, elongated “needle-like” gas voids, micro gas voids, and large circular gas voids. The formation mechanisms of each type are analyzed. The morphology and distribution of gas voids indicate that the solidified pure paraffin structure is anisotropic. The effective thermal conductivity (ETC) of this solid–gas structure is numerically evaluated using lattice Boltzmann simulations, and a two-term power equation is fitted. The results show that the ETC in the vertical direction is significantly lower than in the horizontal direction and the ETC could be reduced by as much as 31.5% due to the presence of gas voids. Full article

In gas transmission stations, flame arrestors are typically installed in pipelines and venting systems to prevent the flames resulting from accidental ignition or deflagration of combustible gases during transmission from propagating through the pipelines. During actual operation, the presence of solid particulates in the gas compromises the flame-arresting efficacy and increases the failure rate of current pipeline flame arrestors. This study employs an integrated approach combining theoretical analysis and numerical simulation to establish a numerical model for flame arrestors that accounts for solid particle deposition effects. The model reveals the distribution characteristics of velocity fields, pressure fields, gas phase volumetric concentration fields, and solid deposition rate fields within pipeline flame arrestors. It systematically investigates the influence mechanisms of porosity, flame arrestor core thickness, inlet flame velocity, arrestor length, particle size, particle concentration on pressure drop, flame arrestment velocity, and deposition rate. These findings provide theoretical support for optimizing flame arrestor structural design and reducing operational failure rates. Full article

In cold-region rock engineering, freeze–thaw cycle-induced crack propagation in fractured rock masses serves as a major cause of disasters such as slope instability. Existing studies primarily focus on the influence of individual fissure parameters, yet lack a systematic analysis of the crack propagation mechanisms under the coupled action of multiple parameters. To address this, we establish three groups of slope models with different rock bridge distances (d), rock bridge angles (α), and fissure angles (β) based on the PFC2D discrete element method. Frost heave loads are simulated by incorporating the volumetric expansion during water–ice phase change. The Parallel Bond Model (PBM) is used to capture the mechanical behavior between particles and the bond fracture process. This reveals the crack evolution laws under freeze–thaw cycles. The results show that, at a short rock bridge distance of d = 60 m, stress concentrates in the fracture zone. This easily leads to the rapid penetration of main cracks and triggers sudden instability. At a long rock bridge distance where d ≥ 100 m, the degree of stress concentration decreases. Meanwhile, the stress distribution range expands, promoting multiple crack initiation points and the development of branch cracks. The number of cracks increases as the rock bridge distance grows. In cases where the rock bridge angle is α ≤ 60°, stress is more likely to concentrate in the fracture zone. The crack propagation exhibits strong synergy, easily forming a penetration surface. When α = 75°, the stress concentration areas become dispersed and their distribution range expands. Cracks initiate earliest at this angle, with the largest number of cracks forming. Cumulative damage is significant under this condition. When the fissure angle is β = 60°, stress concentration areas gather around the fissures. Their distribution range expands, making cracks easier to propagate. Crack propagation becomes more dispersed in this case. When β = 30°, the main crack rapidly penetrates due to stress concentration, inhibiting the development of branch cracks, and the number of cracks is the smallest after freeze–thaw cycles. When β = 75°, the freeze–thaw stress dispersion leads to insufficient driving force, and the number of cracks is 623. The research findings provide a theoretical foundation for assessing freeze–thaw damage in fractured rock masses of cold regions and for guiding engineering stability control from a multi-parameter perspective. Full article

This paper investigates the frost heave and thaw settlement characteristics of the pipe–soil system during the freeze–thaw cycle, along with the underlying mechanisms. A numerical simulation platform for the complex pipe–soil system was developed using the heat conduction equation, moisture migration equation, and stress–strain equation, all of which account for the ice–water phase change process. The simulations were performed with the coefficient-type partial differential equation (PDE) module in COMSOL Multiphysics. By employing coupled thermal–hydraulic–mechanical (THM) simulation methods, the study analyzed the changes in volumetric water content, volumetric ice content, moisture migration patterns, and temperature field distribution of a water pipeline after three years of service under real engineering conditions in the cold region of northern Xinjiang, China. The study also examined the effects of parameters such as pipeline burial depth, specific heat capacity, thermal conductivity, permeability of saturated soil, and initial saturation on the displacement field. The results show that selecting soil layers with high specific heat capacity (e.g., 1.68 kJ/kg·°C) and materials with high thermal conductivity (e.g., 2.25 W/m·°C) can reduce surface frost heave displacement by up to 40.8% compared to low-conductivity conditions. The maximum freezing depth near the pipeline is limited to 0.87 m due to the thermal buffering effect of water flow. This research provides a scientific reference and theoretical foundation for the design of frost heave resistance in water pipelines in seasonally frozen regions. Full article

A theoretical analysis of the influence of the distribution of the local specific energy dissipation rate on the specific interfacial area, the surface and volumetric mass transfer coefficients in apparatuses with heterophase processes and a liquid continuous phase, as well as the quality of mixing in apparatuses with homophase reactions in the liquid phase, is performed. It is shown that the average value of the specific energy dissipation rate over the volume of the device is not a full-fledged criterion for assessing the useful effect since it does not take into account, on the one hand, the local level of energy dissipation in the active zones and, on the other hand, the features of the flow structure and the local residence time in the active zones, depending on the geometry of the device and the method of energy input into it. Limiting cases are discussed: (1) uneven energy distribution in the presence of a small volume with a high specific dissipation rate and (2) ideally uniform energy distribution throughout the entire volume of the device. In the first case, a significant part of the volume is used inefficiently; in the second case, an excessive amount of energy is spent. In this regard, the concepts of dosed distributed energy input for long-term processes and maximum energy concentration in a microvolume for fast-flowing processes are considered. Full article

Egyptian Blue was the first synthetic pigment by humankind. It contains of cuprorivaite, which is a calcium-copper-silicate (CaCuSi₄O₁₀). This study reports the results of a mineralogical and computer tomographic study of Egyptian Blue finds from Aguntum in East Tyrol along with Retznei and Wagna (formerly Flavia Solva) from southern Styria in Austria. The present work aims to extend our understanding of the processes involved in the production of the artificial pigment Egyptian Blue. The samples were investigated with respect to their elemental composition and spatial distribution of the calcium-copper-silicate cuprorivaite CaCuSi₄O₁₀ and then compared with data from previous studies. Thin sections of an Egyptian Blue sphere from Aguntum were examined using optical microscopy (OP), micro-X-ray fluorescence analysis (μ-XRF) and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX). The pigment’s initial mixture as well as the manufacturing process seem to be the decisive factor for the quality of the final product. A relationship between the presence of trace iron (Fe) and titanium (Ti) with the quartz and copper source of the initial mixture is discussed. SEM-EDX analysis revealed that cuprite (Cu₂O) was used as a copper source. In addition, micro-computed tomography (µCT) of the Egyptian Blue finds (Aguntum, Retznei, Wagna-Flavia Solva) was performed. Hence, revealing several concise differences between the samples. Texture and volumetric results show a distinctive difference in cuprorivaite content and particle size. To better analyse the spatial distribution, µCT-3D images of the individual mineral phases identified within each sample were obtained. The clear differences in the results may not only enable a differentiation of the production process but also show another potential of non-destructive µCT for assessment of archaeological findings. Full article

The fiber volume fraction significantly influences the mechanical properties of fiber-reinforced composites. However, accurate measurements can be particularly challenging in natural-fiber-reinforced polymers. This study compared indirect methods using gravimetric and volumetric measurements with a U-Net-based direct method using micro-CT images for flax-fiber-reinforced polymers made via compression molding at 2.33–13.5 bar. A notable discrepancy was observed between the direct and indirect methods, with the latter yielding a fiber volume fraction approximately 25% lower than what could be determined optically. This difference arose from the matrix being absorbed by the fibers, resulting in a mixed region between dry fiber and pure matrix, further explained using a four-phase model. Our findings indicate that the volume fraction depended on the applied pressure. Specifically, we established a linear relationship between the fiber volume fraction and the pressure up to 9.4 bar, beyond which the fiber volume fraction plateaued. Furthermore, we examined the impact of void distribution in relation to pressure. At lower pressures, voids were distributed irregularly throughout the composite, whereas at higher pressures, the overall number of voids decreased, and they tended to concentrate primarily in the center. Full article

To enhance the mechanical properties and high-temperature performance of cordierite–mullite composite ceramics, yttrium oxide (Y₂O₃), a rare earth metal oxide, was employed as a sintering aid to fabricate these composites via in situ synthesis and non-pressure sintering. This study systematically investigated the formation mechanisms of the cordierite and mullite phases and examined the effects of yttrium oxide on the densification behavior, mechanical properties, volumetric stability, and thermal shock resistance. The results indicate that incorporating yttrium oxide (1.5–6.0 wt%) not only promoted the formation of the cordierite phase but also refined the microstructure and enhanced the thermal shock stability at a sintering temperature of 1350 °C. An optimal addition of 3 wt% yttrium oxide ensures that the primary phases are cordierite and mullite, with a microstructure characterized by uniformly distributed micropores, hexagonal short-columnar cordierite, and interlocking rod-like mullite, thereby significantly improving both the mechanical properties and thermal shock stability. Specifically, the room-temperature compressive strength increased by 121%, the flexural strength increased by 177%, and, after three thermal shock cycles at 1100 °C, the retention rates for compressive and flexural strengths were 87.66% and 71.01%, respectively. This research provides a critical foundation for enhancing the mechanical properties and high-temperature service performance of cordierite–mullite saggers used in lithium battery cathode materials. Full article

To address the issue of high wear of polymer composites during friction, WSe₂ nanofillers were incorporated into the polymer matrix as a reinforcing phase to enhance heat transfer and improve the composites’ wear resistance. Tannic acid (TA) was grafted onto the surface of WSe₂ through high-energy ball milling, which facilitated the exfoliation of the nanofillers and improved their interfacial compatibility with the matrix material. Tribological experiments revealed that adding 5 wt% TA-WSe₂ reduced the friction coefficient and volumetric wear rate to 0.0065 and 8.7 × 10⁻⁴ μm³/N·m, respectively, representing reductions of 98% and 94% compared to pure PEI. The TA-WSe₂ not only served as a reinforcing phase to enhance heat transfer but also facilitated the timely dissipation of heat generated during friction. Additionally, it formed strong interfacial bonds with both PEI and PTFE, allowing the applied load to be efficiently distributed throughout the composite material. This study offers a practical approach for the functionalization of WSe₂ and the development of ternary composite materials for tribological applications. Full article

A common issue encountered in metal powder injection molding is the separation of the powder and binder during the injection process, which can give rise to a number of defects. In order to investigate the phenomenon of phase separation in stainless-steel injected flat parts, a numerical simulation methodology was employed by using the Moldex3D R14.0 finite element software to simulate the injection process. Then, the impact of injection parameters on separation was analyzed by comparing key performance indicators such as powder volumetric concentration and density. Furthermore, the extent of the separation was minimized by the optimization of process parameters. The simulation results indicate that the separation of binder and powder is most severe near the gate, where the binder percentage is the highest. The application of elevated mold temperatures, augmented injection rates and reduced injection temperatures can effectively mitigate the two-phase separation phenomenon and enhance the uniformity of powder distribution. This provides a crucial theoretical foundation and technical support for the enhancement of the quality and performance of metal powder injection products. Full article

In exploring adjuvant therapies for head and neck cancer, hyperthermia (40–45 °C) has shown efficacy in enhancing chemotherapy and radiation, as well as the delivery of liposomal drugs. Current hyperthermia treatments, however, struggle to reach large deep tumors uniformly and non-invasively. This study investigates the feasibility of delivering targeted uniform hyperthermia deep into the tissue using a non-invasive ultrasound spherical random phased array transducer. Simulations in 3D patient-specific models for thyroid and oropharyngeal cancers assessed the transducer’s proficiency. The transducer consisting of 256 elements randomly positioned on a spherical shell, operated at a frequency of 1 MHz with various phasing schemes and power modulations to analyze 40, 41, and 43 °C isothermal volumes and the penetration depth of the heating volume, along with temperature uniformity within the target area using T10, T50, and T90 temperatures, across different tumor models. Intensity distributions and volumetric temperature contours were calculated to define moderate hyperthermia boundaries. The results indicated the array’s ability to produce controlled heating volumes from 1 to 48 cm³ at 40 °C, 0.35 to 27 cm³ at 41 °C, and 0.1 to 8 cm³ at 43 °C. The heating depths ranged from 7 to 39 mm minimum and 52 to 59 mm maximum, measured from the skin’s inner surface. The transducer, with optimal phasing and water-cooled bolus, confined the heating to the targeted regions effectively. Multifocal sonications also improved the heating homogeneity, reducing the length-to-diameter ratio by 38% when using eight foci versus a single one. This approach shows potential for treating a range of tumors, notably deep-seated and challenging oropharyngeal cancers. Full article

Surface layers of agricultural machinery working bodies are subjected to intensive abrasive wear during operation, which leads to rapid wear of equipment and reduction of its service life. To increase the wear resistance of the working surfaces of tools, the method of induction cladding using ‘Sormait-1’ materials is widely used. However, after coating, additional heat treatment is required, which improves physical and mechanical properties of the material and increases its durability. When using electrofriction technology (EFT) hardening, the surface of the parts is subjected to melting under the influence of electric arcs, which affects the surface characteristics of the coatings. In this work, two types of surface treatment of L53 steel were investigated: induction cladding using ‘Sormait-1’ material, as well as a combination of induction cladding and subsequent electrofriction treatment. The coatings were characterized and compared with the substrate in terms of the following parameters: microstructure, phase composition, hardness distribution, and friction-wear characteristics. After induction cladding of the Sormait-1 material, a dendritic structure was formed; however, subsequent electrofriction treatment resulted in a reduction of this dendritic structure, which contributed to an increase in the hardness of the material. The average hardness of the coatings after electrofriction treatment was 786 HV_0.1, which is more than three times the hardness of the substrate. Furthermore, the influence of structural characteristics and hardness on abrasive wear resistance was examined in accordance with ASTM G65 international standards. Field tests were conducted on plough shares before and after electrofriction hardening to evaluate their performance. Each ploughshare was scanned with a structured 3D scanner before and after use in the field. From the scan data, the cutting-edge profile was calculated and three key parameters were determined: linear wear, volumetric wear, and mass reduction. According to the results of field tests, it was found that the service life of the blades hardened by electrofriction technology was 12%–14% higher compared to serial blades processed by induction cladding with the use of ‘Sormait-1’ material. Operational tests of hardened plough shares confirmed the results of laboratory tests and proved the advantages of electrofriction technology for increasing the wear resistance of soil tillage machine working bodies. Full article

Fragipans are dense subsurface soil layers that severely restrict root penetration and water movement. The presence of shallow fragipan horizons limits row crop production. We hypothesized that the roots of cover crop might improve soil physiochemical properties and biological activity, facilitating drainage and increasing effective soil depth for greater long-term soil water storage. To evaluate annual ryegrass as one component of a cover crop (CC) mix for promoting the characteristics and distribution of soil water, on-farm studies were conducted at Marion and Springerton in southern Illinois, USA. Soil samples were collected at 15 cm increments to 60 cm (Marion) and 90 cm (Springerton) depths during the fall of 2022. Both sites had low total soil carbon and nitrogen contents and acidic soil pH (≤6.4). A soil water retention curve was fitted using the van Genuchten equation. At Springerton, the CC treatment increased saturated (thetaS) and residual (thetaR) soil water contents above those of the no cover crop (NCC) at the 60–75 cm and 75–90 cm depths. Changes in volumetric soil water content were measured using a multi-depth soil water sensor for the Springerton site during late July to early August of the soybean growing phase of 2022; NCC had higher soil water than CC within the 0–15 cm depth, but CC had higher soil water than NCC at the 30–45 cm depth. These findings indicate that cover crop mix has the potential to improve soil water movement for soils with restrictive subsoil horizon, possibly through reducing the soil hydraulic gradient between the surface and restrictive subsurface soil layers. Full article

Oil-in-water (O/W) nanoemulsions offer significant potential for protecting and delivering sensitive ingredients such as chia seed oil, which is rich in ω-3 fatty acids (approximately 64% α-linolenic acid, ALA). This research work aimed to study the in vitro fat digestibility of chia O/W nanoemulsions (Cas1000) with 10% (w/w) of chia oil and 2% (w/w) of sodium caseinate prepared by microfluidization (1000 bar, 3 passes) and characterized through their droplet size, superficial droplet charge, and global stability. In terms of the in vitro fat digestibility, three different matrices were studied: a water solution of sodium caseinate, a chia O/W nanoemulsion, and a bulk chia oil. The particle size distribution, mean diameter, and microstructure were evaluated after in vitro stomach and small intestine simulation according to the INFOGEST method. Free fatty acids (% FFA) produced during lipolysis were quantified at the end of digestion through their neutralization by acid-base volumetric assay. The droplet size of the Cas1000 had slight changes during the gastric phase while a significant variation of this parameter was observed at the end of the intestinal phase. A higher %FFA was obtained in Cas1000 compared to bulk chia oil with values of 58.26 and 38.13%, respectively. The ALA content in the lipid phase was quantified at the end of the gastrointestinal digestion process. The results indicated no significant changes compared to the initial oil, suggesting no losses of active compounds during digestion. Full article

Lacustrine shale reservoirs hold promise for CO₂ geological sequestration and enhanced shale gas/oil recovery, while the CO₂ adsorption capacity and its controlling factors are still unclear in lacustrine shales. Using a volumetric-based adsorption apparatus, CO₂ adsorption experiments were performed at 50 °C on the Ch7 lacustrine shale samples from the Yanchang Formation in Ordos Basin, China. Basic petro-physical experiments, low-temperature N₂ adsorption, and field emission scanning electron microscopy were used to characterize shale properties and fractal pores in the lacustrine shales. Further, the effects of shale compositions and fractal pores on CO₂ adsorption capacities were serially investigated. The results show that Ch7 lacustrine shales are characterized by being rich in their TOC (total organic carbon) content, high in their clay content, but low in their quartz content, which is distinguished from the mineral compositions in marine shales. The pore size distributions are multi-modal with a main peak and two secondary peaks. Meanwhile, two-regime pore fractal characteristics were identified in the Ch7 lacustrine shales, and the fractal dimensions of the pore surface and spatial structure were calculated based on the FHH (Frenkel–Halsey–Hill) model with D₁ and D₂ ranging from 2.586–2.690 and 2.756–2.855, respectively. CO₂ adsorption isotherms present an initial phase of rapid adsorption followed by a slow saturation and were fitted using the Langmuir model with Langmuir volumes in the range of 2.16–6.89 cm³/g for Ch7 lacustrine shales. TOC is crucial for enhancing the CO₂ adsorption capacity, whereas the effect of clays on CO₂ adsorption is complex because of the reverse effects of clay-related pores and other pores filled by clays. Micropores (<2 nm) dominate the CO₂ adsorption capacity because they offer a larger unit-specific surface area and possess a higher adsorption potential compared to meso- (2–50 nm) and macro- (>50 nm) pores. Moreover, the D₁ is positively related to the CO₂ adsorption capacity as a larger D₁ coincides with more heterogeneous fractal pore surfaces and more available locations for CO₂ adsorption. This work provides useful knowledge and important data for estimating the CO₂ geological storage potential in lacustrine shale reservoirs. Full article