Search Results (732)

To investigate the influence of salt transport in water–steam mixtures on flow and heat transfer and to ensure the operational safety of steam injection boilers, this study simulated the behavior of high-dryness steam carrying salts in U-tubes. The analysis focused on three representative substances—silica, hematite, and calcium carbonate—to evaluate their effects on flow and heat transfer characteristics under varying conditions. The simulation results show that under specified operating conditions, vortices induced by rotational flow lead to complex flow behavior in U-tubes, with transitions from stratified flow to annular flow and back to stratified flow. The effects of salt precipitation on the temperature, velocity, and pressure fields of the boiling flow were also examined. The findings indicate that for pure water, large gradients and multiple vortices adversely affect flow stability, whereas the introduction of small amounts of salts provides localized stabilization in regions of the fluid away from the wall. Full article

Repurposing end-of-life hydrocarbon wells for geothermal energy generation offers a cost-effective and sustainable strategy to expand low-carbon energy deployment while utilizing existing infrastructure. Fracture-connected horizontal oil and gas well pairs present a promising configuration for enhancing heat transfer in low-permeability reservoirs. Existing modeling approaches, however, lack the ability to simulate transient heat conduction from rock to fluid in such complex fracture pathways. This work develops a mathematical model that couples time-dependent heat conduction in the reservoir rock with convective heat transport within the fractures. This model enables prediction of heat energy productivity of converted well pairs by accounting for realistic boundary conditions and operational parameters. In applying the model to a representative shale gas field in Louisiana, key factors affecting fluid temperature and thermal power output, including fracture geometry, fluid flow rate, and wellbore insulation, were considered. The results demonstrate the feasibility and sensitivity of converting hydrocarbon wells into geothermal energy production, providing critical insight for optimizing such conversions to support the increased demand for clean, sustainable energy. Full article

The global transition to a low-carbon energy system requires innovative solutions that integrate renewable energy production with storage and utilization technologies. The growth in energy demand, combined with the intermittency of these sources, highlights the need for advanced management models capable of ensuring system stability and efficiency. This paper presents the development of an optimized energy management system integrating renewable sources, with a focus on green hydrogen production via electrolysis, storage, and use through a fuel cell. The system aims to promote energy autonomy and support the transition to a low-carbon economy by reducing dependence on the conventional electricity grid. The proposed model enables flexible hourly energy flow optimization, considering solar availability, local consumption, hydrogen storage capacity, and grid interactions. Formulated as a Mixed-Integer Linear Programming (MILP) model, it supports strategic decision-making regarding hydrogen production, storage, and utilization, as well as energy trading with the grid. Simulations using production and consumption profiles assessed the effects of hydrogen storage capacity and electricity price variations. Results confirm the effectiveness of the model in optimizing system performance under different operational scenarios. Full article

With the advancement of battery technology and the promotion of the “dual carbon” policy, electric vehicles (EVs) have been widely used in industrial, commercial, and civil fields, and the charging infrastructure of highway service areas across the country has also shown a rapid development trend. However, the charging load of electric vehicles in highway scenarios exhibits strong randomness and uncertainty. It is affected by multiple factors such as traffic flow, state of charge (SOC), and user charging behavior, and it is difficult to accurately model it through traditional mathematical models. This paper proposes a hierarchical Markov chain Monte Carlo (HMMC) simulation method to construct a charging load prediction model with spatiotemporal coupling characteristics. The model hierarchically models features such as traffic flow, SOC, and charging behavior through a hierarchical structure to reduce interference between dimensions; by constructing a Markov chain that converges to the target distribution and an inter-layer transfer mechanism, the load change process is deduced layer by layer, thereby achieving a more accurate charging load prediction. Comparative experiments with mainstream methods such as ARIMA, BP neural networks, random forests, and LSTM show that the HMMC model has higher prediction accuracy in highway scenarios, significantly reduces prediction errors, and improves model stability and interpretability. Full article

This paper presents a modular hybrid mathematical model of bacterial fermentation developed by integrating a detailed kinetic model for the central carbon metabolism of Escherichia coli with a simplified four-compartment model of a large stirred bioreactor. The model describes the growth dynamics of E. coli, taking into account the hydrodynamic characteristics of the cultivation environment and spatial concentration gradients. The first module simulates liquid exchange flows between neighboring reactor zones and tracks the spatial distribution of substrate, acetate, dissolved oxygen, and biomass, while the second one, which is a kinetic model, includes main metabolic pathways such as glycolysis, the tricarboxylic acid cycle, and oxidative phosphorylation. Compared to most previous hybrid approaches relying on simplified kinetics, the present model integrates a detailed kinetic representation of E. coli central metabolism and is openly implemented on the BioUML platform, which ensures its reproducibility and extensibility. Numerical simulations reveal how mixing intensity affects concentration gradients and metabolic regimes across the reactor. Additionally, the model was used to identify an optimal mixing regime corresponding to the state where the system first enters the regime of complete aerobic substrate oxidation. The proposed model is applicable for numerical analysis of industrial-scale bioreactors and for predicting metabolic dynamics under various hydrodynamic conditions. Full article

The integration of renewable energy into industrial processes is crucial for reducing the carbon footprint of conventional hydrogen production. This work presents detailed design, optical–thermal simulation, and performance analysis of a solar parabolic dish (SPD) system for supplying high-temperature steam to a Steam Methane Reforming (SMR) plant. A 5 m diameter dish with a focal length of 3 m was designed and optimized using COMSOL Multiphysics (version 6.2) and MATLAB (version R2023a). Optical ray tracing confirmed a geometric concentration ratio of 896×, effectively focusing solar irradiation onto a helical cavity receiver. Thermal–fluid simulations demonstrated the system’s capability to superheat steam to 551 °C at a mass flow rate of 0.0051 kg/s, effectively meeting the stringent thermal requirements for SMR. The optimized SPD system, with a 5 m dish diameter and 3 m focal length, was designed to supply 10% of the total process heat (≈180 GJ/day). This contribution reduces natural gas consumption and leads to annual fuel savings of approximately 141,000 SAR (Saudi Riyal), along with a substantial reduction in CO₂ emissions. These quantitative results confirm the SPD as both a technically reliable and economically attractive solution for sustainable blue hydrogen production. Full article

The construction and maintenance of ecological corridors not only facilitate species migration and gene flow but also enhance ecosystem stability and resilience, providing critical support for achieving global carbon neutrality goals. Despite their importance, research on urban ecological corridors—specifically their role in carbon sequestration and emission reduction within urban environments—remains insufficiently explored. To address this gap, we employed bibliometric and network analysis methods, utilizing the CiteSpace6.3.1 visualization tool to systematically review existing literature from the Web of Science Core Collection database. This study examines the research progress and trends in urban ecological corridors from 2000 to 2023, focusing on their role and significance in the context of global carbon neutrality. The findings reveal the following: (1) Research attention has grown steadily from 2000 to 2023, with climate change, carbon emission dynamics, and biodiversity emerging as core themes, reflecting increasing global focus on the carbon neutrality functions of urban ecological corridors. (2) CiteSpace analysis identified key research hotspots through keywords including climate change, carbon cycle, ecosystem services, model simulation, and ecological network analysis, revealing the functional mechanisms and pathways of urban ecological corridors in carbon neutrality contexts. (3) Current scientific challenges focus on understanding three core aspects of urban ecological corridors, the compositional elements, spatial structural design, and functional capacity assessment, requiring systematic theoretical breakthroughs. (4) Future research should prioritize exploring mechanisms to enhance urban ecological corridor functions and constructing low-carbon urban ecological networks, providing theoretical guidance and practical pathways for achieving urban emission reduction and climate goals. This study contributes to integrating research on the effectiveness of urban ecological corridors and carbon sinks, offering theoretical insights and practical guidance for reducing urban emissions and achieving climate goals. Full article

Ammonia–coal co-combustion has emerged as a promising strategy for reducing carbon emissions from coal utilization, although its underlying reaction mechanisms remain insufficiently understood. The Chemkin simulation of zero-dimensional homogeneous reaction model and entrained flow reaction model was employed here, and the ROP (rate of production) and sensitivity analysis was performed for analyzing in-depth reaction mechanisms. The nitrogen conversion pathways were revealed, and the mechanisms were simplified. Based on simplified mechanisms, molecular-level reaction pathways and thermochemical conversion networks of nitrogen-containing precursors were established. The results indicate that NO emissions peak at a 30% co-firing ratio, while N₂O formation increases steadily. The NH radical facilitates NO reduction to N₂O, with NH + NO → N₂O + H identified as the dominant pathway. Enhancing NNH formation and suppressing NCO intermediates are key to improving nitrogen conversion to N₂. This paper quantifies the correlation between NO_x precursors such as HCN and NH₃ and intermediates such as NCO and NNH during ammonia–coal co-firing and emphasizes the important role of N₂O. These insights offer a molecular-level foundation for designing advanced ammonia–coal co-combustion systems aimed at minimizing NO_x emissions. Full article

This study explores the combustion behavior of three biomass pellet types—wood (W), sunflower husk (SH), and a mixture of wood and sunflower husks (W/SH)—in a residential hot water boiler. Experiments were carried out under two air supply regimes (40%/60% and 60%/40% primary to secondary air) to measure flue gas concentrations of oxygen (O₂), carbon monoxide (CO), and nitrogen oxides (NO_x). The results indicate that SH pellets generate the highest emissions (CO: 1095.3 mg/m³, NO_x: 679.3 mg/m³), while W pellets achieve the lowest (CO: 0.3 mg/m³, NO_x: 194.1 mg/m³). The mixed W/SH pellets produce intermediate values (CO: 148.7 mg/m³, NO_x: 201.8 mg/m³). Overall boiler efficiency for all tested fuels ranged from 90.3% to 91.4%. Numerical simulations using ANSYS CFX (2024 R2 (24.2)) were performed to analyze temperature distribution, flue gas composition, and flow fields, showing good agreement with experimental outlet temperature and emission trends. These findings emphasize that both pellet composition and air distribution significantly influence efficiency and emissions, offering guidance for optimizing small-scale biomass boiler operation. Full article

The escalating global demand for primary energy—still predominantly met by conventional carbon-based fuels—has led to increased atmospheric pollution. This underscores the urgent need for alternative energy strategies capable of reducing carbon emissions while meeting global energy requirements. Hydrogen, as a clean combustible fuel, offers a promising alternative to hydrocarbons, producing neither soot, CO₂, nor unburned hydrocarbons. Although nitrogen oxides (NO_x) are the primary combustion by-products, their formation can be mitigated by controlling flame temperature. This study investigates the viability of hydrogen as a clean energy vector by simulating an unsteady, turbulent, non-premixed hydrogen jet flame interacting with an air co-flow. The numerical simulations employ the Unsteady Reynolds-Averaged Navier–Stokes (URANS) framework for efficient and accurate prediction of transient flow behavior. Turbulence is modeled using the Shear Stress Transport (SST k-ω) model, which enhances accuracy in high Reynolds number reactive flows. The combustion process is described using a presumed Probability Density Function (PDF) model, allowing for a statistical representation of turbulent mixing and chemical reaction. The simulation results are validated by comparison with experimental temperature and mixture fraction data, demonstrating the reliability and predictive capability of the proposed numerical approach. Full article

This study carried out a detailed investigation into the potential application of hydrothermally treated bituminous coal (hydrochar) as an injectant in blast furnace (BF) ironmaking. A tuyere model was constructed through simulation methods, and the influence of hydrochar injection on the thermal conditions within the BF hearth was also thoroughly analyzed. The results show that the gas flow velocity at the lower part of the tuyere of hydrochar injection increases, and the residual carbon mass fraction of the tuyere decreases. As the oxygen-enriched concentration increases, the CO concentration decreases. The CO concentration in the swirl zone after hydrochar injection is the highest, reaching 43.93%. The distributions of CO and CO₂ exhibit opposite tendencies. Following hydrochar injection, a marked rise in temperature is observed. At an oxygen enrichment level of 30%, the tuyere zone temperature associated with hydrochar injection peaks, surpassing 2700 K. The corresponding pulverized coal burnout rate is also the highest. Thus, the injection of hydrochar has a positive impact on the air flow and temperature field, which can effectively maintain the heat balance and is conducive to strengthening BF smelting. Full article

To elucidate the hydrochemical characteristics and evolution mechanisms of shallow groundwater in the alluvial–coastal transitional zone of the Tangshan Plain, 76 groundwater samples were collected in July 2022. An integrated approach combining Piper and Gibbs diagrams, ionic ratio analysis, multivariate statistical methods (including Pearson correlation, hierarchical cluster analysis, and principal component analysis), and PHREEQC inverse modeling was employed to identify hydrochemical facies, dominant controlling factors, and geochemical reaction pathways. Results show that groundwater in the upstream alluvial plain is predominantly of the HCO₃–Ca type with low mineralization, primarily controlled by carbonate weathering, water–rock interaction, and natural recharge. In contrast, groundwater in the downstream coastal plain is characterized by high-mineralized Cl–Na type water, mainly influenced by seawater intrusion, evaporation concentration, and dissolution of evaporite minerals. The spatial distribution of groundwater follows a pattern of “freshwater in the north and inland, saline water in the south and coastal,” reflecting the transitional nature from freshwater to saline water. Ionic ratio analysis reveals a concurrent increase in Na⁺, Cl⁻, and SO₄²⁻ in the coastal zone, indicating coupled processes of saline water mixing and cation exchange. Statistical analysis identifies mineralization processes, carbonate weathering, redox conditions, and anthropogenic inputs as the main controlling factors. PHREEQC simulations demonstrate that groundwater in the alluvial zone evolves along the flow path through CO₂ degassing, dolomite precipitation, and sulfate mineral dissolution, whereas in the coastal zone, continuous dissolution of halite and gypsum leads to the formation of high-mineralized Na–Cl water. This study establishes a geochemical evolution framework from recharge to discharge zones in a typical alluvial–coastal transitional setting, providing theoretical guidance for salinization boundary identification and groundwater management. Full article

SiCp/Al composites (Silicon Carbide Particle-Reinforced Aluminum Matrix Composites), due to their light weight, high strength, and superior wear resistance, are extensively utilized in aerospace and other sectors; nonetheless, they are susceptible to tool wear and surface imperfections during machining, which negatively impact overall machining performance. Supercritical carbon dioxide minimal quantity lubrication (SCCO₂-MQL) is an environmentally friendly and efficient lubrication method that significantly improves interfacial lubricity and thermal stability. Nonetheless, current lubrication models are predominantly constrained to gas–liquid two-phase scenarios, hindering the characterization of the three-phase lubrication mechanism influenced by the combined impacts of SCCO₂ phase transition and ultrasonic vibration. This study formulates a lubricant film thickness model that incorporates droplet atomization, capillary permeation, shear spreading, and three-phase modulation while introducing a pseudophase enhancement factor β_ps(p,T) to characterize the phase fluctuation effect of CO₂ in the critical region. Simulation analysis indicates that, with an ultrasonic vibration factor Af = 1200 μm·kHz, a lubricant flow rate Q_f = 16 mL/h, and a pressure gradient Δp_tot = 6.0 × 10⁵ Pa/m, the lubricant film thickness attains its optimal value, with Δp_tot having the most pronounced effect on the film thickness (normalized sensitivity S = 0.488). The model results align with the experimental trends, validating its accuracy and further elucidating the nonlinear regulation of the film-forming process by various parameters within the three-phase synergistic lubrication mechanism. This research offers theoretical backing for the enhancement of performance and the expansion of modeling in SCCO₂-MQL lubrication systems. Full article

Against the backdrop of global energy crises and accelerated urbanization, urban wind energy has garnered increasing attention through its integration with building environments. This study investigates the synergistic optimization of architectural parameters (including floor layouts, three-dimensional forms, and roof configurations) with wind capture efficiency. By employing parameterized design and multi-scale flow field analysis, we systematically examine how architectural morphology modulates wind fields and enhances energy performance. Our key findings reveal the following: spatially arranged floor plans significantly influence wind speed distribution; three-dimensional form openings effectively enhance wind velocity while reducing wind-induced vibration responses; and roof configurations and floor layouts demonstrate the highest contribution to wind energy efficiency, with curved roofs showing particularly notable power generation improvements in low-wind environments. The building “density + layout angle + roof form” collaborative strategy has been validated for practical implementation. Current limitations include simulation errors in complex geometries, efficiency bottlenecks in vertical axis turbines, and inadequate lifecycle assessments. Future efforts should focus on multi-field coupled simulations, integrated turbine–architecture design, and enhanced low-carbon evaluation systems to facilitate the transformation of buildings into distributed energy production entities. Full article

The current study explores the applicability of a single constitutive equation, based on the Arrhenius hyperbolic sine model, to a wide range of chemical compositions and test conditions by using a unique approximation. To address this challenge, a mixed model is proposed, integrating a physical model with phenomenological expressions to capture the strain and strain rate hardening, forming temperature, dynamic recovery (DRV) and dynamic recrystallization (DRX). The investigation combines high-temperature mechanical testing with modeling in order to understand the hot deformation mechanisms. Hot torsion tests were conducted on ten different low-carbon steels with distinct microalloying additions to capture their responses under diverse initial austenite grain sizes, deformation temperatures and strain rate conditions (d₀ = 22–850 µm, T = 800–1200 °C and $\dot{\epsilon }$= 0.1–10 s⁻¹). The developed constitutive equation has resulted in a robust expression that effectively simulates the hot behavior of various alloys across a wide range of conditions. The application of an optimization tool has significantly reduced the need for adjustments across different alloys, temperatures and strain rates, showcasing its versatility and effectiveness in predicting the flow behavior in a variety of scenarios with excellent accuracy. Moreover, the model has been validated with experimental torsion data from the literature, enhancing the applicability of the developed expression to a broader spectrum of chemical compositions. Full article