Energy Science & Engineering最新文献

Overburden bed separation grouting (OBSG), a green mining method, can prevent coal-mining subsidence reduction and protect the environment of mining areas. The 3101 working face of a coal mine was adopted as the object to study its overburden structure and subsidence reduction mechanism. A 2D physical similarity simulation test was used to analyze the failure, stress field evolution, and displacement evolution of overlying strata movements under OBSG. Compared with the overlying strata structure in caving mining, the subsidence reduction mechanism of mining under OBSG was revealed. The stress growth was insignificant in stress-concentrated areas, while the stress reduction was apparent in the stress-relaxed area. The deformed region of overlying strata expanded slowly with a greater maximum vertical displacement than the caving method. Surface subsidence above the grouting layer was low, while that below was high. In summary, the slurry formed a dense support body under OBSG in the bed-leaving space. The structure provided upward support and compacted overlying strata, which prevented key strata from fracturing under self-weight stress and minimized surface subsidence caused by coal mining. The results provide a theoretical foundation for enhancing OBSG in subsidence control during mining.

In low-permeability reservoirs, the development of a barrier significantly influences fluid migration and remaining oil distribution during CO₂ miscible flooding. Thus, a comprehensive study of the migration characteristics and dynamic sweep law of the CO₂ miscible flooding front in low-permeability reservoirs with a barrier is crucial for optimizing gas flooding reservoir development design and enhancing oil recovery. Based on the geological features of a low-permeability reservoir block in the Jilin Oilfield, a visualized two-dimensional model with a barrier was designed and fabricated. Then, two sets of CO₂ miscible flooding experiments were carried out using different injection-production modes. By analyzing the dynamic images and the key injection-production parameters during the experiments, the impact of the barrier on oil–gas migration and remaining oil distribution during CO₂ miscible flooding in low-permeability reservoirs was investigated, and the front migration characteristics and dynamic sweep law of the CO₂ miscible flooding in low-permeability reservoirs with barrier were revealed. The results show that: (1) The combined effects of gravity differentiation and barrier significantly influence the migration of oil and gas and the distribution of remaining oil. This impact directly leads to notable differences in the migration characteristics and dynamic sweep law of the flooding front under different injection-production modes. (2) Barrier affects CO₂ displacement through dual mechanisms of interference and obstruction. (3) In this experiment, injecting CO₂ from one side of the barrier achieved better oil displacement results than injecting from the side without a barrier. Therefore, the position of the barrier should be fully considered before actual field production, and a reasonable injection-production scheme should be formulated accordingly to mitigate the negative impact of barriers on the oil recovery. (4) To achieve efficient reservoir development, injection-production parameters should be monitored in real time during CO₂ flooding, and the injection-production rates and positions should be dynamically adjusted based on the flow characteristics of gas flooding.

The study experimentally investigates the primary disintegration of a liquid sheet in an inside-out effervescent atomizer using high-speed flow visualization, focusing on the effects of bubbly flow. Key stability parameters, such as breakup length and frequencies, were analyzed in the Rayleigh zone (We_g < 0.4) and the first wind-induced regime (0.4 < We_g < 5.4). For low gas Weber numbers, the disintegration process exhibited prolonged primary breakup events and shorter intermediate breakups. The coexistence of sinusoidal and dilatational modes of interfacial instability and their roles in these breakup processes were also examined. Increasing the gas Weber number promoted continuous bubble formation, eliminating intermediate breakup events and dilatational modes, thereby enhancing primary breakup efficiency. In the Rayleigh zone, liquid sheet disintegration is primarily driven by the liquid's inherent momentum. However, as gas velocities increase (We_g > 0.4), the momentum of the gas bubbles becomes dominant. A gas-to-liquid momentum ratio, which accounts for the effective area of aeration holes where gas mixes with the co-flowing liquid, was introduced. This ratio, replacing the traditional gas-to-liquid ratio, better captures the initial flow dynamics at the nozzle exit. Dimensionless stability characteristics plotted against this ratio enable data collapse and yield universal functions. Notably, a stronger correlation for breakup frequencies and disintegration length was achieved in the first wind-induced zone compared to the Rayleigh zone, owing to the effective gas momentum. Though the Rayleigh zone generally results in larger droplets, the size can be fine-tuned by modifying parameters like liquid viscosity, surface tension, and the gas-to-liquid ratio. This provides flexibility to tailor the atomization process to specific application needs. Additionally, integrating the Rayleigh zone with other regimes, such as wind-induced breakup, can enable the development of hybrid atomization systems that achieve an optimal balance between energy efficiency and finer droplet size distributions.

PCMs store thermal energy during phase transitions without temperature changes, making them valuable for various thermal applications. When direct PCM use isn't practical, researchers have developed encapsulation methods as an alternative approach. Computational models can simulate various aspects including temperature patterns, species movement, fluid behavior, phase change regions, transport coefficients, energy utilization, and thermal performance metrics. This study explores the thermodynamic and flow characteristics of double-diffusive convection in systems where nano-encapsulated phase change materials are suspended in elliptical tube configurations, with additional consideration of exothermic chemical reactions. The investigation considers parameters including Rayleigh values (10³–10⁵), Lewis number (0.1–10), Hartmann number (0–50), buoyancy proportions (1–5), NEPCM densities (0.01–0.035), relative melting points (0.1–0.9), Stefan number (0.1–0.9), magnetic field alignments (0°–90°), and Frank-Kamenetskii number (0–2.5). Analysis shows that NEPCM concentration and magnetic field properties significantly affect both thermal-hydraulic efficiency and entropy development. The complex relationships between parameters (Ra, FK, Le, Nz, ϕ, Ha) reveal their significant roles in determining heat transfer effectiveness and irreversibility formation.

This study explores the role of import trade in reducing China's domestic carbon emissions—an area often overlooked in climate policy design. Using 2020 data from China's noncompetitive input–output tables and sectoral energy consumption statistics, the analysis reveals significant variation in carbon emission reduction intensity across sectors. Notably, industries such as petroleum and coking products, metal smelting and pressing, and coal mining exhibit higher reduction intensities, indicating that strategic import expansion in these areas can effectively mitigate domestic emissions. In 2020, China's import trade contributed to a reduction of approximately 1106 million tonnes of carbon emissions, accounting for 12.9% of the country's total production-based emissions. This highlights the substantial role of import trade in China's carbon reduction efforts. However, the relatively small share of imports in high-emission sectors suggests that the current import structure may constrain the overall mitigation potential. To enhance the effectiveness of import trade as a carbon reduction tool, the study recommends measures such as lowering tariffs on carbon-intensive products and strategically increasing imports in targeted sectors. These findings provide valuable insights for policymakers aiming to align trade policy with environmental sustainability.

Solar thermal collector technology is crucial for capturing renewable energy to support sustainable thermal uses. Nonetheless, traditional designs frequently experience optical losses, ineffective thermal storage and variable performance under different levels of sunlight. This review conducts a systematic assessment of the development and categorization of solar thermal collectors, spanning from non-concentrating to high-concentration systems. It emphasizes their thermal efficiency, sustainability, and performance based on application, through an in-depth comparative analysis of their thermal characteristics, optical efficiency, structural progress, and material advancements. This review is unique in its combination of hybrid nanofluids, PCMs, innovative receiver designs, and passive tracking options to emphasize synergistic enhancements. Recent advances in experimental techniques have shown that high-efficiency solar concentrators, such as refractive secondary systems, can achieve optical efficiencies surpassing 90%. When these are paired with heat transfer fluids enhanced by nanofluids, thermal efficiency can be boosted by approximately 53%. Moreover, fully replacing fossil fuel heating with optimized solar thermal systems can lead to CO₂ emission reduction ranging from 69% to 77%. The results emphasize the crucial role of integrating design to enhance performance. This broader implication serves as a guide for creating compact, affordable and highly efficient solar thermal systems designed for both industrial and decentralized uses.

The properties of a semi-closed combined cycle power system make it a better option for this study than an open system, since it turns an open-cycle gas turbine into a pollutant-free power system. Also in the selected cycle, the exhaust is channeled toward a divider rather than being released into the atmosphere, and the exhaust is divided into a separation duct and a return duct by the divider. Part of the exhaust is directed back toward the compressor via the return duct. This study investigates the effect of thermodynamic parameters analysis (turbine inlet temperature, ambient air temperature, pressure ratio, and regenerator effectiveness) on thermal efficiency and specific fuel consumption (S.F.C.) for a semi-closed system. The properties of a semi-closed combined cycle power system make it a better option for this study than an open system, since they turn an open-cycle gas turbine into a pollutant-free power system. Also in the selected cycle, the exhaust is channeled toward a divider rather than being released into the atmosphere. The exhaust is divided into a separation duct and a return duct by the divider. Part of the exhaust is directed back toward the compressor via the return duct. This study investigates the effect of thermodynamic parameters analysis (turbine inlet temperature, ambient air temperature, pressure ratio, and regenerator effectiveness) on thermal efficiency and S.F.C. for a semi-closed gas turbine cycle. The operating conditions are taken into account when determining the analytical formulas for assessing thermal efficiency and S.F.C., which are calculated by using thermodynamic equations. The model is constructed using MATLAB®. The results show that the thermal efficiency is increased due to increased turbine inlet temperature, increased regenerator effectiveness, and decreased ambient air temperature. Conversely, S.F.C. decreases. It was also found that when the pressure ratio was roughly 2, the thermal efficiency rose, while the S.F.C. started to decrease. After this value, the thermal efficiency began to decline gradually, and the S.F.C. increased. Also, as the regenerator's effectiveness increased to roughly 0.95, the data indicate that the thermal efficiency achieved its maximum value of 0.60. and at a turbine inlet temperature of about 1600 K, while the S.F.C recorded a minimum value of 0.1394.

This study numerically investigates thermal transport and fluid dynamics in a triangular cavity filled with a MgO–Ag–H₂O hybrid nanofluid containing an undulating porous fin under electromagnetic field and thermal radiation influences. The governing equations are solved numerically using the Galerkin finite element methodology with Darcy–Forchheimer formulation for porous media representation. A comprehensive parametric study examines the effects of Rayleigh number (Ra, 10³–10⁶), Darcy number (Da, 10⁻⁵–10⁻²), Hartmann number (Ha, 0–80), magnetic field orientation angle (γ, 0°–90°), nanoparticle concentration (φ, 0.005–0.02), heat generation coefficient (λ, 1–5), fin waviness parameter (n_w, 0–6), and radiation intensity factor (Rd, 1–5). The numerical model is validated against established benchmark solutions, demonstrating excellent agreement. Findings demonstrate that increasing Ra substantially improves thermal transport and flow intensity, with the average Nusselt number rising by up to 65% and maximum velocity magnitudes increasing by over 500 times. Electromagnetic field application inhibits thermal transport, with (Nu_av) decreasing by 55.6% as Ha increases from 0 to 80. Magnetic field angle optimization shows that γ = 60° provides better heat transfer than γ = 0° at high Ha values. Nanoparticle addition provides moderate thermal enhancement, with an 11.1% increase in Nu_av as φ increases from 0.005 to 0.02, particularly in low-Ra regimes. Radiation effects become most significant at elevated Ra values, with (Nu_av) nearly tripling as Rd increases from 1 to 5 at Ra = 10⁶. Entropy generation analysis reveals that the Bejan number decreases by 98.7% as Ra increases, indicating fluid friction dominance at higher Ra values. These results offer essential guidance for optimizing thermal management systems involving porous structures, nanofluids, and electromagnetic fields.

In recent years, infrared image-based insulator defect detection technology has been widely applied in the field of online monitoring for power equipment due to its noncontact and high-efficiency characteristics; however, existing algorithms still face issues such as insufficient detection accuracy and low computational efficiency in multistate insulator classification tasks, making it difficult to meet practical engineering requirements; to address these challenges, this paper proposes an improved small-target multidefect detection algorithm Porcelain insulator Small-target Heating defect detection You Only Look Once (PSH-YOLO): based on YOLOv8, it employs a hybrid model of self-attention and convolution to aggregate both convolutional and self-attention features; then applies the MobileViT network to enhance the model's training speed and parameter efficiency, ensuring the overall lightweight nature of the model; additionally incorporates a bidirectional feature pyramid network to improve accuracy through multilevel feature pyramids and bidirectional information flow; finally, utilizes the Inner-WIoU loss function to effectively reduce oscillations during training while further enhancing the model's accuracy; to obtain test data, this paper conducted infrared imaging experiments on defective insulators to capture images under varying conditions; experimental validation confirms that the proposed multidefect small-target YOLO algorithm, PSH-YOLO, achieves an average accuracy improvement of 6.17%, with Giga Floating-point Operations Per Second reduced to 7.1, fulfilling the requirements for identifying small-target insulator defects, while ablation and comparative studies demonstrate the effectiveness and superiority of the proposed algorithm.