Search Results (19,441)

In wind tunnel testing, an active vibration suppression system based on piezoelectric actuators is an effective means to ensure stable operation. However, in a cryogenic wind tunnel testing environment, the performance of piezoelectric actuators degrades significantly when they are exposed to cold temperatures and subjected to uneven cooling. This is particularly problematic during real-time changes in the attack angle of a test model. To ensure the reliable operation of wind tunnel tests, an active–passive hybrid thermal control method is proposed in this paper. First, the insulation and heating structure was designed based on the thermal analysis results. Then, combining simulation and measured data, the temperature field was reconstructed in real time using a recurrent neural network algorithm. Next, considering the non-uniform heat dissipation of the system, a thermal allocation module was designed based on digital–physical integration to actively control the overall and localized heat. Finally, a heat preservation performance test platform was established to conduct cooling experiments in a small-scale cryogenic wind tunnel. The results indicated that the proposed thermal control method reduced the average cooling rate of the system by 97% and improved the overall temperature uniformity by approximately 94.23%. Full article

Alpine permafrost and seasonally frozen ground threaten the long-term safe operation of highway infrastructures. Aiming at the structural performance optimization of prefabricated corrugated steel plate retaining walls in alpine permafrost regions, this study adopted finite element numerical simulation combined with field test validation to systematically explore the influences of wall height, plate thickness, corrugation geometry, and tie reinforcement layout on structural deformation and internal force, and carried out targeted parameter optimization. The core innovations include the following: (1) Structural lateral displacement and internal force rise nonlinearly with the increase in wall height, and high retaining walls exhibit an accelerated growth trend of deformation and stress. (2) Increasing plate thickness can effectively reduce structural displacement and stress, while the improvement effect gradually weakens after exceeding a critical thickness. Specifically, when the thickness increases from 4 mm to 5 mm, the displacement decreases by 33.13%. (3) Appropriately increasing corrugation pitch and height improves structural equivalent stiffness and optimizes stress distribution. Increasing the corrugation pitch from 75 mm to 400 mm and corrugation height from 25 mm to 150 mm reduces the maximum horizontal displacement by 52.6%. This demonstrates that larger corrugation profiles significantly improve structural stiffness. For walls higher than 6 m, the spacing should be reduced to 0.8 m × 1.0 m to provide additional lateral restraint. (4) Furthermore, seasonal freeze–thaw cycles and a non-uniform temperature field significantly amplify structural displacement and stress. After 12 months of freeze–thaw cycles, the maximum horizontal displacement increases by 49.7% and the maximum equivalent stress increases by 56.9% compared to the initial state. This study clarifies the parameter control mechanism and temperature coupling effect and provides a reliable theoretical basis and design reference for the engineering application of prefabricated corrugated steel plate retaining walls in alpine permafrost areas. Full article

Climate warming, pavement heat storage and lateral heat intrusion accelerate active-layer deepening and uneven thaw settlement along permafrost transportation corridors. In wide asphalt embankments, heat is stored across a broad pavement-embankment section, while slope-aspect solar input drives asymmetric thermal erosion toward the sunny-side toe. Existing embankments protected by two-phase closed thermosyphons (TPCTs) are commonly evaluated by temperature reduction, maximum thaw depth or local cooling efficiency, but these metrics do not describe frozen-state continuity or residual weak zones. This study develops a three-dimensional hydrothermal model to compare a no-TPCT reference embankment, a conventional inclined TPCT layout and a base-arranged novel horizontal TPCT layout under long-term regional warming. Without TPCTs, the year-20 thaw depth reached 10.06 m at the sunny-side shoulder and 9.76 m beneath the centerline, with thermal disturbance propagating toward the sunny-side toe. Both TPCT layouts stabilized the 0 °C isotherm beneath the embankment. The inclined layout generated deep localized cooling, whereas the horizontal layout formed a more continuous shallow frozen zone, with longer operating durations and year-20 annual cumulative cooling capacities of 1870 and 1600 MJ on the sunny and shaded sides, respectively. The findings support an assessment based on frozen-state continuity, cross-sectional temperature uniformity and residual weak-zone development. Base-arranged novel horizontal TPCTs are better suited to shallow continuity, whereas inclined TPCTs remain useful for deep localized cooling. Full article

Photovoltaic mounting structures operate in harsh environments, demanding high strength and elongation. However, a strength–graded product series within the same composition is lacking. Through Ti microalloying and heat treatment, we developed steels with strengths of 500–800 MPa and studied annealing effects at 640–740 °C. Scanning Electron Microscope (SEM) shows ferrite and cementite: with increasing temperature, ferrite changes from elongated to equiaxed via recovery and recrystallization, while cementite remains finely dispersed along grain boundaries. Transmission Electron Microscope (TEM) reveals TiC precipitates, which decrease in number but increase in size at higher temperatures. Grain refinement strengthening, dislocation strengthening, and precipitation strengthening are the primary strengthening mechanisms, contributing 91.2% and 94.4% to the yield strength after annealing at 640 °C and 720 °C, respectively. Within a wide annealing temperature range, the tensile strength fully covers the 550–650–750–800 MPa grades, with the corresponding elongation fluctuating between 12.4% and 25.3%, achieving a good strength–ductility balance. In summary, simply adding a single Ti element and adjusting the annealing temperature allows for the production of test steels with strengths ranging from 500 to 800 MPa and matched elongation. This approach not only reduces costs but also provides experimental evidence for the process development of a series of new steels for photovoltaic mounting brackets. Full article

Metal hydrides can safely store hydrogen in the solid state at high volumetric density under moderate temperature and pressure. Their hydrogen sorption characteristics are represented by pressure–composition–temperature (PCT) curves. AB₅–type metal hydrides, which have low plateau pressures, store and release hydrogen at low pressures. AB₂–type metal hydrides, which have high plateau pressures, store and release hydrogen at relatively high pressures. Compared with AB₅–type metal hydrides, AB₂–type metal hydrides generally have lower raw material costs and higher hydrogen storage capacity. This makes them more suitable for storing large quantities of hydrogen. Green and blue hydrogen are produced using commercial alkaline water electrolyzers and natural gas reformers, respectively. After downstream purification, this hydrogen is typically supplied at pressures below 1 MPa. However, the high plateau pressures of AB₂–type metal hydrides make it difficult to store this low-pressure hydrogen directly. AB₅–type metal hydrides can store it but release it only at low pressures. A single hydride type therefore operates within a narrow pressure range for both storage and delivery. In this study, a multipurpose hydrogen storage system (MHSS) using AB₅– and AB₂–type metal hydrides was proposed to broaden the applications of metal hydride-based systems. The feasibility of the MHSS was experimentally evaluated through lab-scale tests. The AB₅ and AB₂ modules were first tested as standalone units. The integrated MHSS was then tested assuming that waste heat was continuously available. The MHSS can store a large quantity of low-pressure hydrogen and deliver it across a wide pressure range. This range covers diverse end uses, from fuel cells at 0.5 MPa to hydrogen pipelines at 4.0 MPa. Full article

Ambient-curing epoxy–urethane reactive polymer composites require a balance between initial flowability and subsequent structure buildup. In this study, epoxy–urethane reactive polymer composites containing precipitated calcium carbonate were prepared and referred to as EUPC formulations. Their rheological evolution was characterized by flow sweep, temperature sweep, time sweep, three-interval thixotropy tests (3ITT), amplitude sweep, and oscillatory time sweep. The formulations exhibited distinct initial flow resistance and strong temperature sensitivity, with apparent viscosity decreasing as temperature increased. During ambient curing, viscosity increased continuously, indicating progressive rheological buildup under the selected testing conditions. The 3ITT results showed high-shear-induced apparent viscosity reduction followed by recovery-stage viscosity evolution after returning to the low-shear condition, indicating that the recovery index should be interpreted as an apparent post-shear recovery index rather than a purely thixotropic recovery parameter. Oscillatory measurements revealed a gradual transition from viscous-dominated to more elastic-dominated behavior, and the apparent gel time followed the sequence EUPC-2 < EUPC-4 < EUPC-1 < EUPC-3 < EUPC-5 < EUPC-6. These results indicate that EUPC processability and structure buildup should be evaluated by integrating initial viscosity, temperature sensitivity, post-shear response, and operational viscous-to-elastic transition. Full article

Accurate prediction of the potential habitat distribution of Scomber japonicus, an important target species in China’s distant-water fisheries, is essential for fishing ground forecasting. Using catch data for S. japonicus collected from Chinese large-scale purse-seine and trawl fisheries in the Northwest Pacific Ocean from May to November during 2015–2024, this study applied the maximum entropy model (MaxEnt) and the genetic algorithm for rule-set production (GARP) model to predict the potential habitat distribution of S. japonicus in the Northwest Pacific Ocean. The area under the receiver operating characteristic curve (AUC) and the true skill statistic (TSS) were used to evaluate model performance. The MaxEnt model predicted a relatively concentrated highly suitable habitat, whereas the GARP model identified a broader highly suitable area. To reduce the bias and uncertainty associated with single-model predictions, the outputs of the MaxEnt and GARP models were integrated using a weighted ensemble approach, with the optimal weights for MaxEnt and GARP determined as 0.7:0.3. The ensemble model achieved higher predictive performance, with an AUC of 0.983 and a TSS of 0.840. The highly suitable habitat of S. japonicus was mainly concentrated within 147° E–156° E and 40° N–44° N. Chlorophyll concentration, sea surface temperature (SST), and temperatures at depths of 150 m and 200 m were the main environmental variables affecting the potential habitat distribution of S. japonicus in the MaxEnt model. These findings provide useful information for resource utilization, fishing ground forecasting, and sustainable management of S. japonicus in the high seas of the Northwest Pacific Ocean. Full article

Severity factors are widely used to compress torrefaction temperature–time history into a single scalar descriptor. However, whether such scalar representations are structurally sufficient to describe realised conversion across heterogeneous biomass samples remains unclear. In this study, we evaluated the adequacy of single-scalar severity descriptors using a literature-derived dry torrefaction dataset comprising 154 observations from 7 published studies, covering multiple biomass categories and operating conditions. A severity factor, SF(α), was formulated, and its scaling parameter α was optimised through a systematic α-sweep to maximise its relationship with the experimentally determined extent of conversion (EOC). Based on the optimised formulation, EOC was decomposed into severity-implied conversion (SIC) and conversion offset (CO), separating the dominant severity-controlled trajectory from sample-specific deviations. The optimised formulation (α* = 65.1) showed a strong global correlation with EOC (R2 = 0.8593), confirming that severity captures the main average conversion trend. However, nested model comparisons showed that including CO consistently improved explanatory power for both absolute fuel properties and enhancement ratios, with the greatest gains in enhancement space. SIC and CO accounted for 85.9% and 14.1% of the total variance, respectively, indicating that a non-negligible component of conversion variability was not captured by the single severity descriptor. These results show that, although a single severity scalar is useful for describing dataset-level trends, it does not fully resolve sample-level torrefaction behaviour within the analysed dataset. The SIC–CO framework is therefore proposed not as a new severity index or a pre-measurement predictive model, but as a post hoc diagnostic framework for identifying the explanatory limits of scalar severity representations in biomass torrefaction analysis. Full article

Photosynthetic biogas upgrading (PBU) using microalgae is a promising biological approach for converting raw biogas into biomethane while recovering nutrients and fixing part of the biogenic CO₂ into algal biomass. Unlike conventional physicochemical technologies, which mainly separate CO₂ from CH₄, PBU can combine gas upgrading with wastewater or digestate treatment, nutrient recycling, and biomass production. This review assesses the current state of PBU technology, with particular emphasis on high-rate algal ponds, absorption columns, and closed photobioreactors. It examines the main operating parameters that control gas–liquid mass transfer, carbonate buffering, and photosynthetic activity, including the liquid-to-gas ratio, pH, alkalinity, temperature, light regime, light intensity, and gas retention time. Special attention is given to the combined effects of the L/G ratio, pH, and alkalinity, as these parameters strongly influence CO₂ absorption, CH₄ enrichment, and O₂ contamination of the upgraded gas. The use of wastewater or anaerobic digestate instead of synthetic growth media is identified as an important sustainability advantage, particularly at wastewater treatment plants with existing anaerobic digestion and nutrient-rich side streams. However, digestate use may also create operational challenges related to turbidity, ammonium inhibition, solids, and variable composition. Available studies indicate that PBU may reduce operating costs and greenhouse gas emissions under favorable conditions while creating additional value from algal biomass. Nevertheless, wider deployment is still limited by high land requirements, seasonal variability, O₂ contamination, biomass harvesting, and limited evidence from large-scale systems. Future development should therefore focus on improved oxygen management, more efficient reactor designs, nanoparticle-assisted enhancement of photosynthetic activity, better integration with wastewater treatment, and AI-supported monitoring and control to improve process stability and support scale-up. Full article

This study explores the selection of a heat recovery system for cogeneration units based on gas engines supplying the district heating system in Opole in order to enhance the efficiency and sustainability of the system. The proposed modifications focus on utilizing low-temperature (LT) waste heat from engine cooling circuits and improving exhaust heat recovery. The research examines retrofitting three cogeneration engines (total thermal capacity of 7.6 MW) by integrating water-to-water heat pumps to upgrade low-temperature waste heat (55–45 °C up to 700 kW), enhancing heat supply to the district heating network. Additionally, a second stage of economizers is evaluated to maximize condensation-based exhaust heat recovery from the existing 95–135 °C system. These system modifications increase the overall thermal capacity up to 9–9.1 MW. To maintain heat supply during cogeneration unit shutdowns (due to failures or electricity price fluctuations), an auxiliary air-to-water cascade heat pump provides an additional 0.8–1 MW. With increasing electricity price volatility, these system modifications provide crucial operational flexibility. Computational simulations confirm that the hybrid configuration successfully upgrades waste heat while strictly maintaining the existing engine return water safety limit. The evaluation demonstrates high economic profitability alongside stable emission reductions. This research presents a case study in optimizing heat recovery in cogeneration-based district heating networks, demonstrating practical and scalable applications for sustainable energy systems. Full article

This paper proposes an intelligent time-series early warning framework based on a production LSTM–Transformer network for petrochemical refining processes. A cascaded encoder–decoder architecture is designed, where the LSTM extracts local temporal patterns and medium-term memory from noisy industrial data, while the Transformer models global dependencies and cross-unit interactions via multi-head self-attention. An adaptive feature fusion layer bridges the representational gap between the two networks. A multi-stage preprocessing pipeline tailored for refining MES data handles missing values, outliers, and mixed operating conditions. Using 120 variables from five units of a fluid catalytic cracking unit, the framework predicts the regenerator bed temperature up to 8 h (48 steps) ahead. Comparative experiments show that the production LSTM–Transformer achieves a mean MAE of 0.088, a mean RMSE of 0.113, and the lowest median MAPE of 19.91% among all models, outperforming standalone LSTM (MAE 0.095, MAPE 20.85%) and Transformer (MAE 0.088, MAPE 20.49%). Robustness analysis confirms stable performance under strong noise (down to 5 dB) and missing rates up to 50%, with a median MAE of 0.1027 across tags. This work provides an effective, end-to-end predictive early warning solution that balances accuracy, production importance coverage, and industrial robustness, offering a generalizable data-driven paradigm for process industries. Full article

This paper presents a parametric numerical study on the cooling performance of photovoltaic panels using water and an Al₂O₃-based nanofluid. The increase in operating temperature leads to a decrease in electrical efficiency, making thermal management a key factor in optimizing these systems. The analysis was carried out through numerical simulations in ANSYS, aiming to evaluate the influence of volumetric flow rate and inlet temperature of the cooling fluid on the panel cooling time under transient conditions. The results show that the performance of the Al₂O₃ nanofluid depends on the flow rate of the cooling fluid. At a low flow rate of 0.05 m³/h and a concentration of 4%, the cooling time is reduced by approximately 18–22% compared to water, while this advantage diminishes as the flow rate increases. A favorable operating region was also observed within the investigated laminar and near-transitional range, beyond which increasing the flow rate produced only limited additional reductions in cooling time under the assumptions of the numerical model. The findings highlight the importance of correlating the thermophysical properties of the fluid with flow parameters in order to optimize the thermal management of photovoltaic panels. Full article

The synergistic co-production of ceramic fibers from fly ash and coal gangue offers a promising path for their high-value utilization. However, research in this area remains limited, hindering its broader application. This study employs numerical simulations to assess the influence of high-wheel rotational speed and melt temperature on the mass of inter-wheel melt transfer, as well as their effects on ligament size and slag-ball fraction. The results show that the high wheel, responsible for melt pre-fragmentation and transfer, plays a crucial role in determining the mass of inter-wheel melt transfer and controlling ligament dimensions. In contrast, the low wheel does not directly affect ligament size but aids in transforming pre-fragmented droplets into ligaments and modulates their dispersion. Melt temperature impacts both transfer mass and ligament size by modifying melt properties. The slag-ball fraction increases with the melt temperature and decreases with the high-wheel speed, while the low-wheel speed has a negligible effect. Under the optimal operating conditions of a melt temperature of 1745 °C and equal rotational speeds of 10,000 rpm for both the high and low wheels, a ligament structure with a relatively concentrated size distribution is obtained, with the slag-ball fraction effectively controlled within the range of 8–13%. Full article

The detection of bolt preload force is of vital importance for ensuring the structural reliability of equipment under extreme operating conditions. Traditional ultrasonic transducers based on bulk piezoelectric materials suffer from poor long-term coupling stability and high brittleness of the material, which limits their practical applications. In this work, AlN piezoelectric thin films were fabricated by RF magnetron sputtering, and the effects of RF power and target-to-substrate distance on film morphology, crystal structure, and ultrasonic response were investigated. The results show that increasing RF power increased the film thickness and deposition rate, reduced the detected O content on the film surface, and changed the XRD response. The film deposited at 900 W generated ultrasonic longitudinal wave echoes with a relatively high signal amplitude among the tested RF powers. Among the tested target-to-substrate distances, the film deposited at 60 mm showed a relatively higher deposition rate and generated an ultrasonic longitudinal wave echo with a relatively higher amplitude. The measured d₃₃ value of this film was approximately 4.8 pC/N. The AlN thin-film ultrasonic transducers prepared under the selected deposition conditions were directly deposited on bolts, and the effects of temperature and axial load were calibrated using the ultrasonic TOF measurement method. There was a linear correlation between the TOF and the temperature (R² > 99.99%), as well as between the TOF and the axial load. These results indicate that the deposited AlN thin-film transducer has potential for bolt preload measurement in wind turbine bolts. Full article

Thermal comfort in mixed-mode buildings is challenging due to individual differences in perception, particularly in humid subtropical climates. In Florianópolis, Brazil, dynamic indoor conditions influence occupants’ thermal perception and adaptation. This study investigates how thermal disposition shapes comfort perception. A total of 1032 responses from heat-sensitive users and 733 from cold-sensitive users were collected through electronic questionnaires. The data were analysed using Predicted Mean Vote (PMV), Actual Mean Vote (AMV), and a linear mixed-effects model. Although both groups exhibited average PMV values within the ASHRAE 55 comfort range, their subjective evaluations differed significantly: heat-sensitive users reported warmer sensations, whereas cold-sensitive users reported cooler sensations under similar conditions. Among heat-sensitive users, the PMV–AMV correlation was moderate and strongest under air-conditioning, whereas it was weak and non-significant for cold-sensitive users. Dissatisfaction levels frequently exceeded 20% among heat-sensitive users. Adaptive comfort analysis indicated that most observations fell within acceptability limits for mixed-mode buildings. The mixed-effects model confirmed that thermal disposition significantly moderates the relationship between operative temperature and thermal sensation. These findings highlight the importance of incorporating individual thermal sensitivity into occupant-centred comfort assessments. Full article