Bed Structure Research Articles

Numerical Investigation of Pore Characteristics in Compacted Sand Layers—Physical Interpretation of Applicability of Kozeny-Carman Equation

Accurate evaluation of permeability in subsurface media is essential for solving problems in various fields, such as environmental and petroleum engineerings. This study aims to numerically investigate the pore characteristics of spherical particle beds imitating compacted sandstones for the physical understanding of the permeability change with porosity. In this study, the structures of monodisperse and polydisperse particle beds are simulated and the pore regions are extracted using various numerical methods. The pore characteristics such as effective porosity, tortuosity, and specific surface area in the bed are quantified. The permeability is then calculated by substituting them into the Kozeny-Carman equation. The obtained permeability is compared with measurement results from actual sandstones. The respective pore characteristics are also evaluated against findings from previous studies. The role of pore characteristics in influencing permeability is investigated to examine changes in permeability in compacted sandstones. Consequently, the respective pore characteristics are modeled as functions of porosity. The effective porosity and tortuosity obtained from the present analysis aligns with both experimental results and the physical models proposed in previous studies. The specific surface area also agrees with the previous experimental results. However, the model proposed in the previous research does not match the experimental and present numerical results at low porosity. Therefore, we develop a new geometric model for specific surface area under low porosity conditions. Based on the numerical results, we assess the applicability of the original Kozeny-Carman equation to actual sandstones composed of deformed particles and analyze its physical interpretation. The results suggest that the rapid increase in tortuosity and the rapid decrease in specific surface area with decreasing porosity cause the Kozeny-Carman equation to maintain its original form even in compacted sandstones.

Anisotropy in shear failure of shale: An insight from microcracking to macrorupture

Anisotropic shear failure in shale is crucial to wellbore instability and hydraulic fracturing. While previous studies have examined bedding angles ranging from 0° to 90°, the intermediate angles have not been thoroughly investigated, with limited quantitative analysis from microcracking to macrorupture. To address this gap, we conducted direct shear tests on cubic shale samples with seven bedding angles (α = 0°, 15°, 30°, 45°, 60°, 75°, and 90°) using an innovative combination of acoustic emission (AE) and digital image correlation (DIC) techniques. This approach allowed us to gain a comprehensive understanding of the cracking damage process from the interior to the surface. Under various normal stresses, the minimum peak shear strengths occurred at α = 0°, while the maximum values were observed at α = 45° or 60°, rather than remaining constant. The internal friction angle peaked at α = 45°, not at α = 30° as previously reported. Furthermore, the shear failure pattern was influenced by complex interactions among nominal shear plane, bedding structure, and normal stress. The primary strain concentration zones and microfractures formed not only along the nominal shear plane but also along the bedding planes. Notably, microcracking damage initiated most readily at α = 0°, where the b value in AE events was higher and the fractal dimension was lower. At α = 30°–60°, the b value reached its minimum, while the fractal dimension peaked. The more random distribution of larger-scale microcracks was associated with an increase in the shear strength. These findings provide critical insights into the anisotropy of shear failure in shale and demonstrate the potential of microcracking analysis in predicting critical macrorupture and shear resistance. The identification of three distinct shear failure mechanisms further enhances our understanding of shale anisotropy.

Thicker or Shorter Bark Fragments of Eucalypt Tree Species Make More Densely Packed Fuel Beds, Which Slow Down Fire Spread

Many eucalypt trees shed their bark annually. This bark becomes a component of the litter layer, which acts as fuel, especially during surface fires. The amount and quality of shed bark vary greatly among species, which might have important effects on forest surface fire behavior. In this study, we aimed to compare the bark fuel bed flammability of eight eucalypt tree species and tried to link their bark litter traits via the surface fuel bed structure to bark flammability. In controlled laboratory burns, three flammability parameters, the fire spread rate, total burning time, and maximum temperature, were measured. The bark litter traits included length, curliness, thickness, dry matter content, tissue density, carbon content, nitrogen content, and terpene content, while the litter bed packing ratio and packing density were also measured. We found significant differences in bark traits and flammability among species. Thicker bark fragments of the eucalypt tree species had higher packing densities in fuel beds, a slower fire spread, and a longer burning time. This relationship was strongly driven by the thick bark fragments of Eucalyptus punctata DC. Still, also within the other seven species, bark thickness was the strongest predictor of bark fuel bed flammability, with some additional explanatory power for bark length. For the first time, our study demonstrates that bark traits, particularly litter fragment thickness and length, drive bark litter flammability of eucalypt tree species through their effects on bark fuel bed structure. These findings contribute to our understanding and predictive power of wildfire behavior in forest stands dominated by different eucalypt species.

Numerical Simulation of Coal’s Mechanical Properties and Fracture Process Under Uniaxial Compression: Dual Effects of Bedding Angle and Loading Rate

In view of the significant influence of bedding structure on the mechanical characteristics and fracture behavior of coal, uniaxial compression discrete element numerical simulation experiments were carried out on coal samples with bedding angles of 0°, 30°, 60°, and 90°, and loading rates of 10−3/s, 10−2/s, 10−1/s, and 100/s, respectively, using PFC 6.0 software. The dual effects of bedding angle and loading rate on the mechanical properties of coal and its damage behavior were analyzed. The results show that (1) as the loading rate increases, the peak strength of the specimen increases, and the damage intensifies. The counts of the three types of cracks increased exponentially, while the crack growth rate was dramatic. (2) With the increase in loading rate, the density of the compressive stress force chain inside the specimen increases and gathers to the two ends, and the density of the tensile stress force chain is basically unchanged but gathers to the middle. The overall strength of the force chain changes according to the law of decreasing and then increasing. (3) With the increase in the bedding angle, the peak strength decreases and then increases, and the curve is approximately “V” shape. When the bedding angle is 60° and 90°, the peak stress is minimum and maximum, respectively. Shear cracks are dominant in the model, and the crack distribution shows a trend of increasing and then decreasing. (4) With the increase in the bedding angle, the density of the compressive stress force chain gradually decreases, and the density of the tensile stress force chain appears to be aggregated. The overall strength of the force chain changes according to the law of decreasing and then increasing.

Experimental Investigation on the Permeability and Fine Particle Migration of Debris-Flow Deposits with Discontinuous Gradation: Implications for the Sustainable Development of Debris-Flow Fans in Jiangjia Ravine, China

The particle size distribution (PSD) is a crucial parameter used to characterize the material composition of debris-flow deposits which determines their hydraulic permeability, affecting the mobility of debris flows and, hence, the sustainable development of debris-flow fans. Three types of graded bedding structures—normal, reverse, and mixed graded bedding structures—are characterized by discontinuous gradation within a specific deposit thickness. A series of permeability tests were conducted to study the effects of bed sediment composition, particularly coarse grain sizes and fine particle contents, on the permeability and migration of fine particles in discontinuous debris-flow deposits. An increase in fine particles within the discontinuously graded bed sediment led to a power-law decrease in the average permeability coefficient. With fine particle contents of 10% and 15% in the bed sediments, the final permeability coefficient consistently exceeded the initial value. However, this trend reversed when the fine particle contents were increased to 20%, 25%, and 30%. Lower fine particle contents indicated enhanced permeability efficiency due to more interconnected voids within the coarse particle skeleton. Conversely, an increase in fine particle content reduced the permeability efficiency, as fine particles tended to aggregate at the lower section of the seepage channel. An increase in coarse particle size decreased the formation of flow channels at the coarse–fine particle interface, causing fine particles to move slowly along adjacent or clustered slow flow channels formed by fine particles, resulting in decreased permeability efficiency. Three formulae are proposed to calculate the permeability coefficients of discontinuously graded bed sediments, which may aid in understanding the initiation mechanism of channel deposits. Based on experimental studies and field investigations, it is proposed that achieving sustainable development of debris-flow fans requires a practical approach that integrates three key components: spatial land-use planning, in situ monitoring of debris flows and the environment, and land-use adjustment and management. This comprehensive and integrated approach is essential for effectively managing and mitigating the risks associated with debris flows, ensuring sustainable development in vulnerable areas.

Local-scale variability in packed beds of polyhedral particles: Structural and thermal distribution

Heat transfer in packed beds largely depends on the bed structure, which is strongly linked to particle shape, yet most prior work focuses on spherical particles. This work contributes towards a better understanding of particle shape effect on the local-scale and its variability. Particle beds are generated numerically and steady-state thermal simulations are conducted for 12 different particle shapes and three particle-to-gas conductivity ratios. Voronoi cells are extracted to obtain local cell porosities; distributions are studied statistically. Another crucial parameter, particle-particle contact areas, are evaluated and compared with shapes. Variability in local structure results in varied temperature profiles. Thermal fluctuations are substantially affected by irregular shapes, an effect that increases for highly conductive particles. Notably, the spatial distribution of phases with different conductance has a strong influence on the distribution of local heat flux. Predominantly, these outcomes also indicate the relevancy of including shape parameters in developing reactors or modeling other granular applications.

Eelgrass (Zostera marina) Trait Variation Across Varying Temperature-Light Regimes

Seagrass trait variation, which results from both local genetic adaptation and phenotypic plasticity, has important effects on ecosystems. Physical drivers underlie these processes and are important determinants of trait variation. Despite this, few studies examine multivariate predictive relationships between sets of physical drivers and sets of seagrass traits. Here, we use redundancy analysis to define this relationship for eelgrass Zostera marina, using traits that represent bed structure, morphology, and physiology and physical drivers that emphasize light conditions and temperature variability on different time scales. We found a relationship between plant size (i.e., leaf length and width, rhizome width, number of leaves) and shoot density that dominated the trait variation. Specifically, as temperatures became warmer, more variable, and light was less limiting, plants became smaller (shorter, narrower, and fewer leaves, thinner rhizomes) but beds became denser. Plant biomass (leaf area index), which increased with decreasing temperature variability and bottom light, further refined this relationship. Overall, temperature variability (i.e., daily temperature range, heat accumulation, time in the optimal temperature range, and tidal and meteorological variability), as well as bottom light, were important predictors of eelgrass traits. We further identified three distinct temperature-light regimes across which traits differed; these included the cool low variability temperature regime with low light, the warm high variability temperature regime with high light, and the intermediate case between these endpoints. Our study identifies specific temperature and light drivers that define certain eelgrass traits and provides a multivariate statistical model that can be used to predict eelgrass trait values from known physical conditions.

Insights into gas-solid flow structures in fluidized beds up to 1600 °C via analysis of gas residence time distributions

This study investigates gas residence time distributions (RTDs) in a fluidized bed of Al₂O₃ particles at temperatures ranging from ambient to 1600 °C, focusing on the impact of temperature on gas back-mixing and flow patterns. We find that at low temperatures (up to 300 °C), gas flows in a near-plug flow pattern, represented by narrow RTD curves with early peaks. As temperature increases to 600 °C, the RTD curves broaden, featuring delayed peaks due to bubble breakup and enhanced gas drag. Between 800 °C and 1200 °C, significant deviations from plug flow emerge, driven by stronger interparticle forces and increased gas transfer to the emulsion phase. Interestingly, beyond 1200 °C, the RTD curves shift back toward plug flow, influenced by intensified interparticle forces and physicochemical changes in the bed materials.

Exploring Geometric Properties and Cycle Design in Packed Bed and Monolith Contactors Using Temperature-Vacuum Swing Adsorption Modeling for Direct Air Capture.

This study presents a comprehensive comparison between the packed bed and monolith contactor configurations for direct air capture (DAC) via process modeling of a temperature-vacuum swing adsorption (TVSA) process. We investigate various design parameters to optimize performance across different contactor geometries, including pellet size, monolith wall thickness, active sorbent content in monoliths, and packed bed structure configurations, considering both a traditional long column (PB40) and multiple shorter columns configured in parallel (PB5). Our parametric analysis assesses specific exergy consumption, sorbent, and volume requirements across different operating conditions of a five-step TVSA cycle. For minimizing sorbent requirements, PB5 and monoliths with over 80% sorbent loading were the best-performing contactor designs with overlapping performance in the low-exergy region. Beyond this region, PB5 faced limitations in reducing sorbent requirements further and was constrained by a maximum velocity at which it is sensible to operate without substantially increasing the exergy demand. In contrast, monoliths decreased sorbent requirements with minimal exergy increase due to reduced mass transfer resistances and lower pressure drop associated with their thin walls. The analysis of volume requirement-specific exergy Pareto fronts revealed that PB5 was less competitive with this metric due to the requirements for additional void space in the contactor configuration. The study also revealed that optimal sorbent loading for reducing volume requirements in monoliths differed from those minimizing sorbent usage, with the most effective loading being below 100%. Thus, the optimal contactor design varies depending on the goals of minimizing sorbent and volume requirements, and the choice and design of the contactor will depend on the relative costs of these factors. Lastly, our findings challenge the assumption that higher velocities are always preferable for direct air capture, suggesting instead that the operating velocity depends on the contactor configuration.

Numerical Analysis on the Excavation Damage Evolutions of Layered Tunnels: Investigations on the Influences of Confining Pressure and Layer Angles.

The bedding structure of layered tunnels has a significant impact on the evolution of excavation damage, yet research on the relevant evolution mechanisms is scarce. In view of this, this paper develops a mesh-free numerical method to simulate the progressive damage process of tunnel excavation and proposes a method for applying stress boundaries within the SPH framework. Through this method, simulations of tunnel excavation damage under different bedding dip angles and stress ratios are conducted. The results show that the following: in the simulation of excavation damage of a tunnel without bedding structures, specific areas around the tunnel exhibit characteristics of tensile-shear composite failure and shear failure, verifying the rationality of the algorithm; under different bedding dip angles, a damage zone is first generated around the tunnel, and shear cracks appear at the tangent of the bedding plane and the tunnel, with the damage degree being the largest when α = 30° and the smallest when α = 45°; and under different stress ratios, the damage starts around the tunnel, continuously evolves, and finally forms a failure zone inside the bedding plane joints tangent to the tunnel, and the damage degree increases with the increase in the stress ratio. This study discusses the damage mechanisms under different calculation schemes and provides a reference for understanding the excavation damage mechanisms of layered tunnels.

The sediment source and formation mechanism of the Paleozoic reservoirs in Western Desert, Egypt

Deep-burial sandstone reservoirs host significant hydrocarbon reserves and are the potential area for petroleum exploration. The deeply buried (>4000–4500 m) Paleozoic reservoirs in Western Desert, Egypt are recently characterized by giant oil and gas discoveries. However, the debates about their sediment sources and formation mechanisms hamper further hydrocarbon exploration and development. Detailed core observations, geochemical and porosity-permeability analyses are performed to fill above gaps. The Paleozoic sandstone reservoirs are well-developed, including the Cambrian–Ordovician Shiffah Formation (av. porosity of 6.6% and permeability of 6.01 mD), Silurian Basur Formation (7.4% and 44.64 mD), and Carboniferous Desouqy Formation (8.7% and 76.44 mD). Their sedimentary facies is predominantly composed of fluvial and coastal facies. The predominant sediment sources for the Paleozoic clastic rocks are the Precambrian medium-acidic felsic basement, while the Precambrian sedimentary rocks provide certain sediment sources based on geochemical data. The development of Paleozoic reservoirs in the Western Desert is the integrated result of a “tri-element control” involving sedimentary facies, diageneses, and tectonic activity. Parallel bedding, cross-bedding and slump structures, and many different types of fossils are well-developed here. These indicate fluvial–coastal facies, which is favorable for the formation of thick sandstone reservoirs. During post-depositional regimes, the Paleozoic is characterized by long-term shallow burial and subsequently rapid deep burial. This contributes to the preservation of pores and the development of fractures. Cementation and compaction reduce the porosity and permeability during burial, while multi-phase dissolution activities (e.g. meteoric diagenesis and organic acid dissolution) increase the reservoir performance. Oil charge is favorable for the preservation of porosity. This leads to better performance of the oil-bearing intervals than reservoir intervals. Moreover, multi-stage tectonic activities are favorable for the development of faults and fractures, thereby increasing reservoir performance. The Paleozoic sandstones show high potential for hydrocarbon exploration and are significant for those concerned with Western Desert.

Particle-resolved computational modeling of hydrogen-based direct reduction of iron ore pellets in a fixed bed. Part II: Influence of the pellet sizes and shapes

Full-fledged computational modeling of Direct Reduction reactors encompasses single-pellets models and the step-wise scaling up to industrial-scale reactors. This study delves into the particle-resolved computational modeling of hydrogen-based direct reduction of 0.5 kg iron ore fixed-beds, as a scale-bridging step and focusing on the influence of pellet sizes and shapes. To investigate the effect of particle sizes, two beds with particles sized 10.0–12.5 and 12.5–16.0 mm were characterized and numerically reconstructed using the discrete element method. While to assess the effect of particle shapes, a third numerical bed was generated directly upon a high-resolution CT-scan of a real bed. Through reactive CFD simulations, we investigated the reduction process in these three beds using hydrogen as the reducing gas. Our findings reveal that the bed structure significantly impacts the reduction efficiency and overall conversion degree. This study emphasizes the importance of accurate bed reconstruction and provides critical insights for optimizing the hydrogen-based direct reduction process in industrial applications.

Particle-resolved computational modeling of hydrogen-based direct reduction of iron ore pellets in a fixed bed. Part I: Methodology and validation

In the pursuit of more sustainable steelmaking, stakeholders are engaging in a transformative exploration of hydrogen-based direct reduction as an alternative to conventional blast furnaces. As a bridging step between single iron ore pellets and industrial shaft furnaces, direct reduction modeling in a fixed bed configuration can play a central role for subsequent process optimization. However, this task involves numerous challenging steps: generation of a realistic packed bed structure along with a good quality mesh and, foremost, reliable transport and kinetic processes for the individual pellets. Therefore, the present work formulates a sound methodology to progress from single particle considerations to 3D-CFD simulations of iron ore reduction using hydrogen in fixed beds, further supported by validations regarding the bed structure and the overall reduction against experimental data from the literature of a 500 g iron ore bed. The current results offer new insights into the direct reduction process, revealing, for instance, the non-uniform reduction of pellets within the bed, the presence of gas pockets, or the importance of the temperature deviation due to the endothermic reduction of iron oxides with hydrogen.

Study on the Dispersion Characteristics of Coal Complex Resistivity under the Effect of Liquid Nitrogen Cyclic Freeze-Thaw and Evaluation of Permeability Enhancement.

The effect of liquid nitrogen freeze-thaw fracturing on coal seams can be potentially evaluated by the complex resistivity method. The real part (Reρ) and the imaginary part (Imρ) of the complex resistivity and permeability of coal were determined under different cycle times and in different bedding directions. The reason for permeability enhancement was discussed, and the dispersion mechanism of complex resistivity during cyclic freeze-thaw fracturing was analyzed. The results indicated that (1) the complex resistivity parameters have a good response to the cycle times; Reρ, |Imρ|, and the dispersion degree (α) are positively correlated with cycle time; the fully polarized frequency (f p) of Reρ, the characteristic frequency (f c) of Imρ, and variation are negatively correlated with cycle time. (2) The difference in complex resistivity parameters between the vertical bedding direction and the parallel bedding direction is significant, and the difference in electrical properties of the bedding structure continuously decreases with the increase in cycle time. (3) Under the effect of liquid nitrogen cyclic freeze-thaw, a complex network of fractures in coal is formed, the anisotropic characteristics of coal are weakened, and effective conductive channels are damaged. The peak frost heave force decreases exponentially with the increase in cycle time, and the difference in bedding electrical properties gradually disappears. (4) Comparing the inversion degree of measured data with three conductive models, ρ0 and τ are selected as the optimum parameters for evaluating the effect of liquid nitrogen cyclic freeze-thaw. A logarithmic permeability evaluation model is constructed based on ρ0 and τ. This work provides a new perspective based on electrical detection for evaluating the permeability enhancement of coal during liquid nitrogen cyclic freeze-thaw.

Length matters: Effects of fishing gear and fishing behavior on the catch efficiency of demersal seines

Raiding seals pose a big problem to gillnet fishers in areas with high seal abundances. As moving to active gears could be a potential solution for that problem, one gear of particular interest in areas with relatively flat sea bed structure is the so-called “MiniSeine” – a demersal seine that is reduced in size so it can be operated from small vessels. Besides its ability to catch most of the species targeted by gillnet fishers, it offers various advantages compared to other active gears. To reduce the gear in size to fit on a small vessel, the present study assessed how seine rope length (4 coils vs 8 coils), seine rope diameter (18 mm vs. 22 mm) and seine net configurations of different sizes and shapes (three different designs) affect the catch efficiency and the ratio of fish below minimum conservation reference size (MCRS). In general, shorter seine ropes (4 coils) resulted in significantly lower catches than longer ones (8 coils), except for the smallest seine configuration. Larger seine net configurations and longer seine ropes caught generally less fish below MCRS, both up to around 10 %. The seine rope diameter did not affect catches significantly. As potential “adjusting screw” to counteract lower catches due to shorter seine ropes, the effect of different layout patterns of the seine ropes on the catch efficiency was assessed. Laying out the second seine rope perpendicular to the first one can increase the fishing area to more than three times while CPUE showed a tendency to be increased compared to the standard layout pattern. Besides its importance for a successful development of the MiniSeine, these findings are of equal interest for the large-scale demersal seine fishery.

Numerical investigation on flow characteristics and heat transfer of mixed convection in a packed bed

Flow characteristic and heat transfer of mixed convection in the packed bed were investigated numerically comparing with the previous experimental studies. For the fixed packed bed and sphere diameters of 0.06 m and 0.01 m, the ratios of bed height to sphere diameter and Reynolds numbers were varied from 5 to 20, and from 1 to 300, respectively for both buoyance aided and opposed flows. The temperatures difference between fluid and sphere was 78.85 K. The packed bed structure was modeled by generating location coordinates through the random number with an in-house code and computational analyses were performed using ANSYS FLUENT software. Laminar mixed convection behaviors were observed: heat transfer enhancement for buoyancy aided flow and impairment for buoyancy opposed flow. For larger bed heights, even under a laminar flow condition, turbulent behaviors were observed: heat transfer impairment for buoyance aided flow and enhancement for buoyance aided flow. The same trend was observed in the analysis of turbulence intensity. Local flow analysis within the packed bed confirmed that this is due to the vortices and the wakes resulting from the interaction between mixed convection flows and the randomly stacked spheres in the packed bed. This study unveiled mixed convection phenomena accompanied by the geometric effects of the packed bed on vortices and wakes, which exhibit turbulence-like behavior.

Comparative analysis of seagrass habitat structure: distinct patterns at semi-enclosed and open sites in South Sulawesi, Indonesia

Habitat structure in the seagrass ecosystems are crucial for coastal biodiversity and substrate stability. The purpose of this research conducted from June to December 2021 in South Sulawesi Province, Indonesia was to examine the habitat structure of seagrass beds at two sites with different levels of exposure: Puntondo (semi-enclosed bay) and Batu Kalasi (exposed). Species identification, non-metric multidimensional scaling (nMDS), Bray Curtis cluster analysis, similarity percentage (SIMPER), Particle Size Analysis (PSA), and satellite imagery were used to evaluate complexity, heterogeneity, sediment particle size, and extent. The presence of macroalgae and coral species at Batu Kalasi, likely related to substrate condition, contributed to significant differences in seagrass community composition. The nMDS and Bray Curtis cluster analyses revealed patterns of complexity, while satellite imagery revealed habitat heterogeneity. Seagrass meadow tracking showed a larger and more patchy area in Puntondo Village, measuring 164,318 m², while in Batu Kalasi Island, it only reached 136,901 m². The findings underscore the need for tailored conservation strategies for seagrass ecosystems, in particular to address the specific challenges observed at each site, emphasizing the importance of understanding and preserving diverse coastal environments.

Advances in research on the ballast bed stability on railway bridges

The rapid development of high-speed railway bridges in China has brought enormous challenges to the ballast bed stability on the bridge. With the increase in the bridge span, the bridge deformation under the temperature load increases gradually, as well as the stability difference of ballast bed between different regions. Moreover, the track vibration response under high-speed driving conditions is larger, which can easily cause differential settlement, flying ballast, and deterioration of the ballast bed, thereby affecting the bearing capacity and stability of the ballast bed. In view of this, this article summarizes relevant research work on a ballast bed on the bridge from the perspectives of the resistance, deformation, and acceleration response of the ballast bed. In addition, this study discusses the existing measures for improving the ballast bed stability on the bridge, including the optimization of the sleeper and ballast bed structures. Finally, the main issues that need to be addressed to improve the ballast bed stability on the bridge are pointed out, and ideas for future research on ballast beds on bridges with different spans and structures are proposed.

Interspecies differences and lake‐specificity in the δ13C and δ18O signatures of charophyte carbonate encrustations

Abstract This study identifies the relationships between the δ13C and δ18O signatures of extant charophyte carbonates (δ13CCARB and δ18OCARB) and the δ13C of dissolved inorganic carbon and δ18O of water (δ13CDIC and δ18OWATER), respectively, and the structure of charophyte beds and the physico‐chemical properties of the ambient water. Inter‐ and intra‐specific differences and lake‐related variability are assessed. Four morphologically different charophyte species (Nitellopsis obtusa, Chara tomentosa, Chara rudis, Chara contraria) were studied in four charophyte‐dominated lakes (Chara‐lakes) in Central Europe. A wide distribution of the species in calcium‐rich freshwater lakes, where they form extensive underwater beds and contribute to the deposition of calcareous sediments, makes the study representative of Chara‐lakes. Charophytes and water above them were sampled monthly (June–September 2008) at permanent study sites. Additionally, three comparative macrophyte‐free pelagic sites were sampled in each lake. For all the charophytes studied, there was a greater variation in the δ13C and δ18O values of the encrustations than of the ambient and pelagic waters. Except for N. obtusa and C. tomentosa, the species differed significantly in the δ13CCARB values. The encrustations were enriched in 13C compared to water DIC. Chara tomentosa encrustations were significantly depleted in 18O compared to N. obtusa and C. contraria. In contrast to Chara species, N. obtusa encrustation was 18O‐enriched compared to surrounding water. The largest isotope differences between carbonate encrustations and surrounding water were found for C. rudis. Considering the δ13CCARB versus δ13CDIC values, only slender species (i.e. N. obtusa and C. contraria) precipitated encrustations close to isotopic equilibrium with water DIC. Based on theoretical δ18OCALCULATED and measured δ18OCARB values, only C. tomentosa precipitated encrustation in equilibrium with the δ18OWATER. Using redundancy analysis, the δ13CCARB values positively correlated with the δ13CDIC and δ18OWATER values and the percent volume of water inhabited by plants. The depth of sites, water mineralisation, alkalinity and fertility were inversely correlated with the δ13CCARB. The redundancy analysis revealed a clear division of samples into species and lakes; lakes were especially distinct. We postulate that the stable C and O isotope compositions of charophyte encrustations are lake‐ rather than species‐specific and that the isotopic signatures of charophyte carbonates are representative of the entire lake epilimnion, not just the vegetated littoral zone. Furthermore, the isotopic signal of bulk sediment can provide environmental information that is as useful as species‐specific isotope values.

Enhancing submicron dust capture in high-temperature flue gases: A computational study on gradient pore-buried tube granular bed filters

Granular bed filters (GBF) represent a highly effective technology for purifying high-temperature dusty flue gases, although their efficiency in capturing submicron particles remains limited. A novel gradient porosity GBF model with varying bed structures and heat exchange capabilities was proposed. In this research, we employed CFD software to elucidate the movement and heat transfer process of 1 μm dust particles within gradient porosity GBFs and heat exchanger tubes. By optimizing the model under the conditions of a 0.5 m/s inlet flue gas flow rate and 1 μm dust particle size, we achieved a 345.62% increase in filtration efficiency and a 76.61% reduction in pressure drop. The findings indicate that the proposed GBF outperforms other models across various flue gas flow rates in terms of filtration efficiency. The impact of the flue gas flow rate on the combined filtration efficiency for submicron dust on the proposed GBF model was notably significant.