Search Results (160)

Compared with gaseous hydrogen at ambient temperature, liquid hydrogen (LH₂) possesses a higher volumetric energy density and is therefore regarded as one of the most economically viable hydrogen storage and transportation options. However, the extremely large temperature difference between the storage temperature of LH₂ and the ambient environment may give rise to serious safety hazards once a leakage accident occurs. Focusing on an integrated hydrogen production and refueling station (IHPRS), this study investigates the suppression effect of a novel synergistic protection system—combining a barrier wall and an air curtain—on LH₂ leakage and dispersion. By comparing the dispersion distances of hydrogen clouds under different barrier wall–air curtain configurations, the optimal synergistic structure was identified as a barrier wall with a planar size of 36 m × 12 m and a height of 3 m, combined with an air curtain velocity of 40 m/s. The reliability of this structure is further evaluated under practical influencing factors: under varying natural wind conditions, the maximum downwind dispersion distance is reduced by up to 58.02%; at a flash evaporation mass fraction of 20%, horizontal dispersion is suppressed by 42.18% and 33.17% in the X- and Z-directions, respectively; and at a leakage mass flow rate of 5.15 kg/s, the X-direction dispersion distance is reduced by 33.88% with a 40.14% increase in cloud height. The results show that the proposed barrier wall–air curtain synergistic protection structure can effectively alter the dispersion path of the FHC (refers to the hydrogen cloud with a volume concentration within the flammable range between 4 and 75% vol) formed by LH₂ leakage, shorten the hazardous downwind distance, and enhance the vertical dispersion of the FHC. These findings provide theoretical support and safety guidance for the risk control of LH2 leakage accidents in IHPRS. Full article

The rapid advancement of intelligent unmanned systems has brought new opportunities to mobile crowd sensing (MCS). Compared with traditional homogeneous frameworks, heterogeneous air-ground collaborative multi-agent frameworks consisting of unmanned aerial vehicles (UAVs) and unmanned ground vehicles (UGVs) exhibit superior flexibility and efficiency in complex sensing tasks. Task allocation among agents is crucial for improving overall MCS quality. To achieve efficient task allocation for heterogeneous collaborative agents, this study investigated two typical complex multi-agent task allocation scenarios with dual optimization objectives: (1) For the Air-Ground Few-Agents-More-Tasks (AG-FAMT) scenario, the objectives are to maximize task completion and minimize total travel distance; (2) For the Air-Ground More-Agents-Few-Tasks (AG-MAFT) scenario (task allocation based on agent locations), the objectives are to minimize total travel distance and travel time cost. Overall, in this paper, we proposed two algorithms: a multi-task minimum cost maximum flow optimization algorithm called Multi-Task Minimum-Cost Maximum-Flow (MT-MCMF) tailored for AG-FAMT, and a multi-objective optimization algorithm called Weighted Integer Linear Programming (W-ILP) for AG-MAFT (with a focus on optimizing UAV charging path planning). Experiments on a large-scale real-world dataset demonstrated that both proposed algorithms outperform baseline methods under varying experimental settings (task quantity, difficulty, and distribution), providing a novel approach to enhance the overall quality of air-ground MCS tasks. Full article

The rapid increase in memory power density has made memory thermal management a critical challenge in high-density servers, where extremely limited DIMM spacing significantly reduces the effectiveness of air cooling. Compared with CPUs and GPUs, memory-level liquid cooling has received less systematic study, particularly regarding the influence of cold plate structural design on thermal and hydraulic performance under realistic server conditions. In this paper, three engineering-feasible memory liquid cooling solutions (water-flowing cold plate, clamp-type cold plate and heat-pipe-based cold plate) are experimentally compared on a high-density server system. Experiments are conducted at coolant inlet temperatures of 37–50 °C with a fixed flow rate of 0.8–1.5 L/min. Memory, CPU, and voltage regulator temperatures, as well as system pressure drop, are measured. Results show that memory temperature increases with coolant inlet temperature for all configurations, while their relative performance remains unchanged. Memory temperatures range from 62.04 to 71.13 °C, 57.65 to 66.98 °C, and 66.22 to 76.07 °C, with corresponding pressure drops of 24.19–26.69 kPa, 32.73–35.98 kPa, and 27.00–29.96 kPa. These results provide insight into the role of coolant distribution and flow-path topology in memory thermal performance. Full article

A major challenge for aircraft fuel cell propulsion systems is to ensure that the air properties on the cathode side remain within a narrow, suitable envelope throughout the flight. The components must maintain almost constant temperature, pressure and humidity levels under widely varying ambient conditions. The choice of components must take into account the aviation-specific requirements for weight and waste heat. In this numerical study, we investigate a novel cathode air supply system for a hydrogen fuel cell propulsion system which replaces the state-of-the-art electrical components used to drive the compressor in the cathode air supply system with a hydrogen-fuelled micro gas turbine. Previous studies have shown the potential of waste heat and overall cathode gas path size reduction but the off-design performance of such system is yet to be investigated. Hence, based on realistic regional aircraft flight missions and realistic atmospheric conditions, we investigate the off-design performance of the propulsion system. Therefore, a constant mass flow algorithm along cathode and gas turbine gas paths is developed and presented. Next, earth observation data are used to determine realistic boundary conditions and air contamination. Based on these data, the possible contaminant ingestion of the fuel cell is evaluated to allow for future sizing of filters for robust operation. Furthermore, the effects of realistic ambient conditions on the thermodynamic cycle yield important information about necessary revisions of the cycle design point. Full article

Agroforestry, where trees and shrubs are planted in row-alley systems, can utilize the natural ability of plants to interact with pollutants and serve as a passive biotechnological method for improving air quality. A method for programming air phytoremediation processes is presented, using appropriately shaped plant structures, considering species characteristics and the spatial configuration of plants in row-alley plantings. The main objectives of this study were: to determine the relationship between pollution reduction and the characteristics of plant communities, considering the parameters of individual plants and group characteristics, to determine strategic parameters for the interaction between plants and pollutant flows, and to identify optimization paths for each stage. The optimization of the air phytoremediation process is presented using the example of changes in the fine particulate matter (PM_2.5) concentration pattern, analyzed through numerical experiments using micrometeorological computational fluid dynamics models (ENVI-met software). Ex-ante analysis of hypothetical scenarios showed that introducing appropriate configurations of variable vegetation structure could lead to pollution reductions of up to 19%. The effectiveness of the presented plant systems qualifies this method as a type of bioengineering technology, supporting the multifunctionality of agroforestry systems. Full article

Push–pull exhaust systems are widely applied for controlling industry-processing fumes, and their performance is fundamentally governed by the coupling interaction among the air-curtain jet (“push”), the buoyant thermal plume generated by the heat source, and the converging flow induced by the exhaust hood (“pull”). However, the dynamic characteristics and design criteria of this coupled flow field under large temperature differences remain insufficiently explored. Here, a series of scaled experiments combined with numerical simulations is conducted to systematically investigate the coupling behavior of the air-curtain jet and the thermal plume, and two quantitative performance indicators, namely plume deflection height and flow rate along the plume deflection path, are proposed to evaluate flow control effectiveness and energy dissipation. An orthogonal experimental design is further employed to analyze the sensitivity of heat-source and air-curtain parameters with respect to these indicators. The results demonstrate that the air temperature reaches its maximum at approximately 0.8 m downstream of the air-curtain outlet, and that both the supply velocity and outlet width of the air curtain are dominant parameters exerting statistically significant influences on plume deflection height and flow rate along the path (p < 0.01). Furthermore, the Archimedes number effectively characterizes the competition between jet inertia and plume buoyancy in the coupled flow field, with its appropriate value preliminarily recommended to be controlled below 40. This study provides quantitative insights for the engineering design of push–pull exhaust systems operating under high thermal load conditions. Full article

Ammonium bisulfate (ABS) fouling in air preheaters has become a critical challenge restricting the safe and efficient operation of coal-fired units. Optimizing the flow field of the outlet of the upstream SCR system is a potentially effective path to mitigate ABS fouling. In this work, CFD simulations were conducted on the SCR De-NO_x system and its succeeding flue ducts connected to the air preheater. The simulation results of the original design show that a significant velocity deviation exists at the inlet of the air preheater (with the CV₁ up to 53.2%), with a portion of the flue gas adhering to the walls, which could induce ABS fouling in the low-temperature region. By adding flow guide plates into the flue duct, the flow uniformity before the air preheater was expected to be effectively improved. Notably, considering the deposition characteristics of ABS and the operating characteristics of the rotary air preheater, this study proposed a novel evaluation indicator, radial variance coefficient (CV₂), which focuses on the velocity uniformity based on the annular sector unit, to indicate the risk of ABS deposition. The influence on velocity uniformity of different flow guide plate layouts was analyzed. Based on the multiple evaluation metrics including pressure drop and flow uniformity, the optimal layout scheme was then selected. After optimization, the radial variance coefficient decreased from 30.7% to 11.7%, with the pressure drop slightly increased from 50 Pa to 80 Pa. This study could help to reduce unit failure frequency and support efficient operation of coal-fired power plants. Full article

This study presents the development of a three-dimensional (3D) filament assembly model for predicting the air permeability of woven fabrics composed of spun yarns. To address the limitations of conventional single-line yarn models, the proposed framework incorporates fiber-level geometric representations using non-uniform rational B-splines (NURBS) and simulates multiple weave patterns—including plain, basket, twill, and rib—under various set density configurations. Each yarn was modeled with accurate filament distribution and cross-sectional layering, enabling the construction of realistic unit-cell-based CAD geometries. Computational fluid dynamics (CFD) simulations were performed using the k-ε turbulence model in SolidWorks Flow Simulation and validated against experimental measurements conducted under ISO 9237:1995 conditions. The filament assembly model achieved high predictive accuracy, exhibiting a lower of percentage prediction errors than the single-line yarn path model, thereby more effectively capturing airflow behavior through inter-yarn and intra-yarn pores. These findings highlight the capability of integrated CAD/CFD methodologies for virtual prototyping of breathable textiles and provide a robust foundation for high-precision performance prediction in functional and technical fabric design. Full article

To investigate how dynamic fluctuations in oxygen concentration—induced by air leakage flow in the goaf—affect the oxidation and spontaneous combustion behavior of residual coal along the airflow path, particularly considering the catalytic and inhibitory roles of CO and CO₂ generated during coal oxidation, a series-connected dual coal sample tank experimental system was developed. Experiments were conducted under controlled thermal conditions: isothermal operation in the upstream coal sample tank and programmed temperature ramping in the downstream tank. Coal oxidation indicators—including O₂ consumption rate, CO/CO₂ generation profiles, heat release rate, and apparent activation energy—were systematically quantified under dynamically varying atmospheric conditions and benchmarked against those obtained under fresh air and fixed-O₂ reference conditions. The results reveal that under dynamic atmospheres—characterized by declining O₂ concentration coupled with accumulating CO and CO₂—coal oxidation deviates markedly from behavior observed under stable, high-O₂ conditions. Crucially, CO and CO₂ are not merely passive oxidation products; they actively modulate reaction kinetics. Specifically, they suppress the dominant chain-propagation reactions of low-temperature oxidation, thereby reducing both oxygen consumption and heat release rates relative to fixed-O₂ controls at equivalent initial O₂ levels. Concurrently, they accelerate the CO-producing pathway, resulting in disproportionately elevated CO yields, even under thermally mild conditions. This decoupling between thermal activity and gaseous hazard implies a heightened risk of CO poisoning and combustible gas accumulation, potentially preceding detectable temperature rise. Accordingly, conventional single-parameter risk assessment frameworks—especially those relying solely on temperature or O₂ depletion—are insufficient for early hazard identification in such complex, transient airflow environments. We recommend integrating real-time CO concentration monitoring as a critical, proactive parameter in spontaneous combustion early-warning systems. Full article

Accurate prediction of air traffic noise is critical for advancing environmentally sustainable operations in high density terminal areas. Conventional noise prediction models often exhibit significant limitations due to discrepancies between actual and nominal flight trajectories. To overcome this challenge, this study introduces a probabilistic framework that integrates real air-traffic-flow data to generate realistic flight trajectory distributions. The proposed methodology extracts key operational features—including trajectory distribution probabilities, and essential trajectory operation features—within a machine learning architecture. Furthermore, we develop a dedicated air traffic noise prediction model for clustered flight paths that explicitly incorporates traffic flow patterns, enabling high-fidelity simulation of noise propagation under actual air traffic operation. The framework is validated using a QAR (Quick Access Recorder) dataset from the terminal area of Changsha Huanghua International Airport. Experimental results demonstrate the model’s high predictive accuracy for both air traffic noise distribution and its influence, coupled with computational efficiency and practical applicability. The findings indicate that the proposed approach successfully addresses the challenge of predicting air traffic noise from divergent, real-world flight trajectories, offering a robust method for supporting noise-abatement strategies and sustainable aviation-planning initiatives. Full article

Natural ventilation is a common cooling strategy in open dairy barns, but its efficiency largely depends on external wind directions and speeds. Misalignment between external airflow and fan jets often led to non-uniform air distribution, reduced local cooling efficiency, and an elevated risk of heat stress in cows. However, few studies have systematically examined the combined effects of wind directions and speeds on airflow and heat dissipation. Most research isolates natural or mechanical ventilation effects, neglecting their interaction. Accurate computational fluid dynamics (CFD) modeling of the coupling between outdoor and indoor airflow is crucial for designing and evaluating mixed ventilation systems in dairy barns. To address this gap, this study systematically analyzed the effects of external wind directions (0°, 45°, 90°, 135°, 180°) and speeds (1, 3, 5, 7, 10 m s⁻¹) on fan jet distribution and convective heat transfer around dairy cows using the open-source CFD platform OpenFOAM. By evaluating body surface airflow and regional convective heat transfer coefficients (CHTCs), this study quantitatively linked barn-scale airflow to animal heat dissipation. Results showed that both wind directions and speeds markedly influenced airflow and heat exchange. Under 0° wind direction, dorsal airflow reached 6.2 m s⁻¹ and CHTCs increased nearly linearly with wind speeds, indicating strong synergy between the fan jet and external wind. Crosswinds (90° wind direction) enhanced abdominal airflow (approximately 5.2 m s⁻¹), whereas oblique and opposing winds (135–180°) caused stagnation and reduced convection. The dorsal-to-abdominal CHTCs ratio ($R_{d/a}$) increased to about 1.6 under axial winds but decreased to 1.1 under cross-flow, reflecting reduced thermal asymmetry. Overall, combining axial and lateral airflow paths improves ventilation uniformity in naturally or mechanically ventilated dairy barns. The findings provide theoretical and technical support for optimizing ventilation design, contributing to energy efficiency, animal welfare, productivity, and the sustainable development of dairy farming under changing climatic conditions. Full article

With the increasing number of highly airtight residences, concerns have risen that the negative pressure formed indoors during kitchen hood operation can reduce capture performance and cause unintended infiltration. This study experimentally and numerically (via CFD simulations) examined whether installing an air supply unit on the cooktop beneath a hood can stabilize hood performance and suppress infiltration in small residential spaces. Two cases were established depending on whether air was supplied: Case 1 (hood operation only) and Case 2 (simultaneous operation of the hood and the air supply unit). In the experimental setup, the hood exhaust flow rate, supply airflow rate, sink-drain infiltration rate, and temperature/humidity were measured. The period during which variations in measured values remained within 10% was defined as the steady state. In the CFD analysis, winter conditions were assumed, and the measured values were applied to the wall boundary, after which the temperature and velocity field were analyzed. In Case 2, by supplying 24.11 CMH of air, the hood flow rate remained stable at 75.72 CMH (98.8% of the initial level) throughout the test, and no infiltration was detected. The CFD analysis revealed that the air supply unit generated an “air curtain” effect, enabling rapid capture of hot airflow and reducing the high-temperature region. In conclusion, the interconnected operation of supply and exhaust systems was shown to be effective in enhancing hood exhaust stability, suppressing unintended infiltration, and improving capture reliability in highly airtight small residential buildings. Future studies should include further analyses, such as the effects of actual cooking behaviors and leakage path distributions. Full article

To address the issue of climate change caused by greenhouse gases, extensive research has been conducted on technologies for separating and capturing carbon dioxide. This study aimed to investigate the internal flow behavior and relative spatial distribution of CO₂-related features inside a vortex tube using the Schlieren method. Due to the presence of numerous components in a typical counter-flow vortex tube that may cause optical refraction along the measurement path, a simplified tube with a single nozzle was designed and manufactured for the experiments. The experiments consisted of CO₂ single-phase flow and air–CO₂ mixture flow tests. Images captured during the experiments were processed using Gaussian filtering and background correction to enhance the visibility of boundary layers and internal flow structures. Based on the pixel intensity values of the processed Schlieren images, relative intensity distributions associated with CO₂-related flow behavior inside the tube were estimated and visualized. The experimental results revealed that, in both CO₂ single-phase and air–CO₂ mixture flows, regions of relatively high Schlieren intensity consistently appeared at specific locations within the tube. These observations indicate that the internal flow structure and relative distribution patterns are sensitive to the local flow features near the nozzle region under the tested conditions. The temporal evolution of the normalized Schlieren pixel intensity and its standard deviation was quantitatively evaluated, in a relative sense, to characterize the development of vortex flow structures under different operating conditions. The proposed visualization and analysis framework provides a systematic qualitative approach, supported by relative quantitative indicators, for investigating vortex-induced flow behavior. This framework may serve as a foundation for future studies that integrate complementary diagnostics and numerical analyses to further explore the vortex-based gas separation mechanism. Full article

The dynamics of gas–liquid two-phase flow at fracture junctions are crucial for optimizing fluid transport in the complex fracture networks of coal seams, particularly for coalbed methane (CBM) extraction and gas hazard management. This study presents a comprehensive numerical investigation of transient air–water flow in a two-dimensional, symmetric, cross-shaped fracture junction. Using the Volume of Fluid (VOF) model coupled with the SST k-ω turbulence model, the simulations accurately capture phase interface evolution, accounting for surface tension and a 50° contact angle. The effects of inlet velocity (0.2 to 5.0 m/s) on flow patterns, pressure distribution, and energy dissipation are systematically analyzed. Three distinct phenomenological flow regimes are identified based on interface morphology and force balance: an inertia-dominated high-speed impinging flow (Re > 4000), a moderate-speed transitional flow characterized by a dynamic balance between inertial and viscous forces (∼1000 < Re < ∼4000), and a viscous-gravity dominated low-speed creeping filling flow (Re < ∼1000). Flow partitioning at the junction—defined as the quantitative split of the total inflow between the main (straight-through) flow path and the deflected (lateral) paths—exhibits a strong dependence on the Reynolds number. The main flow ratio increases dramatically from approximately 30% at Re ∼ 500 to over 95% at Re ∼ 12,000, while the deflected flow ratio correspondingly decreases. Furthermore, the pressure loss (head loss, ΔH) across the junction increases non-linearly, following a quadratic scaling relationship with the inlet velocity (ΔH ∝ V₀^1.95), indicating that energy dissipation is predominantly governed by inertial effects. These findings provide fundamental, quantitative insights into two-phase flow behavior at fracture intersections and offer data-driven guidance for optimizing injection strategies in CBM engineering. Full article

This study used a 3D numerical model to investigate the heat-flow behavior of a 1 MW synchronous motor–generator by creating a conjugate heat transfer model that included the rotating parts. The computational model involved complex solid/fluid interfaces, a rotor–stator gap, and a fan-driven cooling path that passes through a stator’s external flow path in order to identify local temperature fields and flow distributions. Under design conditions, localized high-temperature regions were observed in the rotor coil because the cooling air was heated, and the airflow then diverged through the stator’s internal channels. On the contrary, periodic low-temperature areas were formed around the stator’s circumference as a result of conductive heat diffusion into the outer casing. A correlation was derived describing a relationship where the peak temperature decreased in a clear logarithmic manner as the cooling air mass flow rate increased. We confirmed that a cooling flow rate of at least 2.0 kg/s is needed to keep the rotor coil temperature below 120 °C within its operational limit under design points. Furthermore, the functional form of the temperature–flow rate relationship remained logarithmic, and the correlation coefficients in this relationship changed linearly with heat generation, even under off-design conditions, where the total heat generation was reduced to 88% of the design value and the ambient temperature was lowered. The study results will provide a practical basis for swiftly estimating peak temperature for various operating scenarios and for determining cooling paths and fan geometry to avoid repeating expensive simulations. Full article