Search Results (2,995)

As a representative digital additive construction material, three-dimensional printed concrete (3DPC) imposes a synergistic rheological requirement on fresh cementitious mixtures, namely “pumpability–extrudability–buildability,” throughout the forming process. Rheological parameters and their temporal evolution not only govern the stability of the material during pumping, nozzle extrusion, and layer-by-layer deposition, but also directly determine interlayer interfacial integrity, geometric fidelity, and the development of macroscopic mechanical performance. This paper provides a systematic review of the regulation strategies and evolutionary characteristics of 3DPC rheology, with particular emphasis on how raw material composition, printing parameters, and multiscale evolution mechanisms influence yield stress, plastic viscosity, and thixotropic behavior. The time-dependent evolution of rheological properties is elucidated across multiple length scales, encompassing microscopic particle interactions and hydration-induced bridging, mesoscopic aggregate force-chain networks and particle migration, and macroscopic shear stimulation coupled with temperature–humidity effects. On this basis, it is further highlighted that existing models and characterization frameworks remain insufficient to capture the time-dependent structural evolution under realistic printing conditions. Therefore, the establishment of unified characterization standards, together with in situ rheological measurements and multiscale simulations, is urgently required to enable the coordinated optimization of material design and printing processes and to facilitate engineering-scale implementation. Full article

Droplet size is a key factor in minimizing spray drift. Different types of adjuvants and sprayer operating pressures can affect the droplet size distribution in various ways. This study aimed to evaluate the effects of commercial adjuvants, namely, acids and surfactant (AS), silicone surfactant (SS), organosilicone surfactant (OS), mineral oil (MO and MO₂), and copolymer (CP) adjuvants, on the droplet spectra and physicochemical properties of aqueous solutions. Hydrogen potential (pH), volumetric mass ($VM$), electrical conductivity (EC), surface tension (ST), contact angle (CA), and droplet spectra were measured. The droplet spectrum variables, including volumetric diameters ($D_{v0.1}$, $D_{v0.5}$, and $D_{v0.9}$), the Relative Span Factor ($RSF$), and percentages of the total volume of droplets with a diameter smaller than 100 µm (V100) and larger than 500 µm (V500), were determined using a laser diffraction particle analyzer (Malvern Spraytec). Spraying tests were carried out using the AXI 11003 flat fan nozzle at pressures of (0.1, 0.2, 0.3, 0.4, and 0.5) MPa. The increase in pressure increased the V100 and the $RSF$, with greater sensitivity observed for SS. Adjuvants such as AS, MO₂ and OS showed a more balanced trend, with a smaller increase in fine droplets and a greater reduction in coarse droplets. The principal component analysis (PCA) revealed that the droplet spectrum variables were the ones that best explained the variation among the solutions. A negative correlation was identified between EC and other physicochemical properties, such as pH, ST, and CA. Therefore, these properties alone did not determine the atomization pattern. The study demonstrates that optimizing spray quality and minimizing drift require a combined consideration of adjuvant physicochemical properties and their interaction with operational pressure. Full article

Complementary feeding influences infant growth and health. Māori and Pacific infants in Aotearoa New Zealand experience disproportionate nutrition-related disease, yet complementary feeding data are limited. Caregivers of 625 infants (7–10 months) completed a questionnaire on timing of introduction, baby-led weaning (BLW), and baby food pouch use. Ethnicity was total response; infants not Māori or Pacific were classified as ‘other’. Complementary foods were introduced at around six months for 56.5% of Māori, 62.2% of Pacific, and 80.9% of others; before five months for 40.5%, 34.2%, and 17.3%. BLW prevalence was 29.2% (Māori), 17.1% (Pacific), and 27.3% (other). Although pouches were uncommon when complementary feeding began, by 7–10 months about two-thirds of Māori and Pacific infants were fed pouches sometimes or frequently. Frequent pouch use with mostly or always nozzle feeding occurred in 12.2% of Māori infants, 12.2% of Pacific infants, and 2.7% of other infants. Vegetables and purée were the most common first food and texture. By six months, over half consumed red meat and about half consumed iron-fortified baby rice. These feeding practices have implications for nutrition-related health inequities among Māori and Pacific infants, highlighting the need for culturally centered public health approaches to support whānau with feeding. Full article

This study investigates how torch standoff distance influences the microstructure, surface topography, and progressive-load scratch response of air plasma-sprayed 8YSZ and rare-earth co-doped GdYbYSZ thermal barrier coatings on an St-52 grade carbon steel substrate. Three nozzle-to-substrate spraying distances were examined: 80, 100, and 120 mm. X-ray diffraction revealed that the 8YSZ coatings possessed a predominantly tetragonal (t′) structure, with minor monoclinic fractions detected in the coatings obtained with the 80 mm and 100 mm distance parameters. The GdYbYSZ coatings, in contrast, exhibited a single-phase cubic defect-fluorite structure; their diffraction peaks appeared at lower 2θ angles relative to undoped cubic ZrO₂, consistent with lattice expansion caused by the substitution of Zr⁴⁺ by the larger Gd³⁺ and Yb³⁺ cations. Surface topography was quantified by non-contact laser profilometry, providing areal (Sa) and profile (Ra) roughness parameters for the as-sprayed condition as well as three-dimensional scratch-damage morphology after testing. Progressive-load scratch tests were performed using a Rockwell diamond indenter over a 2 mm track with the normal load ramped from 0.03 N to 30 N. Penetration depth, residual depth, tangential force, and acoustic emission were recorded continuously to identify critical damage transitions. Across all spraying distances, 8YSZ exhibited systematically shallower scratch grooves than GdYbYSZ; end-of-track maximum groove depths remained below 37 µm for 8YSZ, whereas GdYbYSZ reached up to 72 µm under identical loading conditions. The novelty of this study lies in combining torch standoff distance as a processing variable with multi-channel progressive-load scratch diagnostics, including in situ acoustic emission, depth profiling, and friction monitoring, to comparatively assess the scratch wear performance of 8YSZ and rare-earth co-doped zirconia TBCs for the first time. Full article

Modern high-pressure turbine (HPT) nozzle guide vanes (NGVs) operate under non-uniform inlet conditions, including hot streaks and swirl, which can induce complex flow phenomena and uneven thermal loading. These effects, particularly at the hub-vane corner, can compromise NGV durability, yet the combined influence of swirl and film cooling remains underexplored. The objective of this study is to investigate the aerothermal behaviour of contoured first-stage NGVs under varying swirl intensities and directions to improve understanding of hub and corner thermal protection and failure mechanisms. Steady, compressible RANS simulations were conducted with the k-ω SST turbulence model. A vane with a contoured hub and multiple film cooling rows was designed and analysed under axial and swirling inflows, both clockwise and counter-clockwise, with swirl numbers of Sn = ±0.2 and ±0.4. Axial flow achieved the highest area-averaged film cooling effectiveness (FCE) of 0.617. Negative swirl (Sn = −0.4) improved suction-side corner FCE to 0.215 but reduced pressure-side cooling, whereas positive swirl (Sn = 0.4) improved pressure-side cooling but reduced suction-side FCE to 0.043. Corner temperatures under positive swirl reached 1780 K, consistent with promoting failure, while negative swirl reduced corner temperatures to 1516 K. Aerodynamic losses increased with swirl, with negative swirl generating 5.78% higher total pressure losses than the axial baseline. Swirl altered the corner vortex topology, affecting boundary layer interactions and local heat transfer. These results highlight a trade-off between thermal protection and aerodynamic efficiency, emphasising that optimising NGV performance requires careful design of hub cooling and consideration of swirl direction and intensity. Full article

The present study demonstrates a step-by-step method for optimizing the outflow valve geometry and maximizing thrust generation. In this system, the skin-mounted OutFlow Valve (OFV) acts as a convergent–divergent nozzle and, as such, the De Laval nozzle equations are considered as guidance for the shape optimization. The performance of the skin-mounted flapped OFV optimized designs is assessed with a combination of analytical equations and Computational Fluid Dynamics (CFD) methods. The three-dimensional Reynolds-Averaged Navier–Stokes (RANS) yield reliable thrust recovery estimates and reveal key aspects of the aerodynamic flow behaviour through the valve, highlighting the interaction between the skin-mounted flapped OFV components. The results compare well with the analytical approach, providing a basis upon which a skin-mounted flapped OFV can be tailored for a specific mission. Full article

Open-air asphalt milling generates hazardous respirable crystalline silica (RCS), posing severe risks to operators of legacy machines lacking enclosed cabs. This study evaluates a novel, standalone retrofit water spray system designed to intercept fugitive dust. Field validation across 11 road maintenance sites involved particle characterization and paired system-off/on exposure monitoring. Results indicated a Mass Median Aerodynamic Diameter (MMAD) of 6.12 µm, confirming the efficacy of fine-atomizing nozzles (0.3 mm) for capturing respirable fractions. The system achieved RCS suppression efficiencies ranging from 60% to over 85% under low-to-moderate wind conditions (<2.5 m/s). A comparative analysis revealed no significant performance gain from larger 0.5 mm nozzles, supporting the use of smaller orifices for optimal water conservation. However, suppression efficacy degraded significantly when crosswinds exceeded 2.5 m/s, indicating a potential operational boundary. This retrofit solution provides a scientifically validated, cost-effective engineering control for reducing occupational silica exposure in aging road maintenance fleets. Full article

Three-dimensional printed concrete (3DPC) has emerged as an innovative construction technology for extreme environments, offering advantages in thermal insulation, reduced labor requirements, and rapid construction. However, this layer-by-layer deposition process brings interlayer effects that affect mechanical anisotropy, permeability, and thermal performance, posing challenges for structural reliability. This review systematically examines current methods for characterizing and mitigating interlayer effects in 3DPC. Material-related factors—including admixtures, aggregates, recycled materials, fibers, and geopolymer incorporation—alongside process parameters such as printing speed, nozzle geometry, layer height, interlayer time, and environmental conditions, are analyzed for their influence on interlayer quality. State-of-the-art techniques for evaluating interlayer voids, mechanical behavior, and thermal performance are summarized. Moreover, results from micro-imaging, mechanical testing, and heat transfer assessments are also introduced. Ultimately, strategies for optimizing material composition and printing parameters to improve interlayer bonding and overall performance are highlighted. Overall, this paper provides a methodological framework to guide the design, testing, and practical implementation of 3DPC in demanding engineering applications. Full article

This article presents the design and detailed characterization of a new supersonic wind tunnel at the Aerospace Laboratory for Lasers, ElectroMagnetics, and Optics of Texas A&M University, tailored for optical diagnostic development and sub-scale fundamental compressible fluid dynamics research. A Ludwieg tube tunnel architecture was selected due to its robustness, versatility, and low operational costs. The tunnel consists of a 50-foot-long driver tube constructed from modular Tri-Clamp spools, a Mach 4 nozzle with 3 in. exit diameter configured as a free jet, and a fast-acting valve with 14 ms opening time for high-duty-cycle operation. Such construction proved to be a robust, compact, and affordable solution for academic applications. Characterization methods consisted of simultaneous high-speed dot-schlieren, total and static pressure measurements, and femtosecond laser electronic excitation tagging. Average flow velocity for the first steady-state test time was measured via FLEET at (668.0 ± 5.7) m/s. The Mach number was calculated based on the angles of the attached oblique shocks formed near the 30° cone model. Calculated Mach number was repeatable from run to run and had small oscillations near the average value of 3.96 ± 0.03. Based on the simultaneously measured velocity and Mach number, the static temperature was calculated to be between (68.6 ± 0.3) K and (66.3 ± 0.3) K throughout the 400 ms test time, completely defining the thermodynamic state of the generated freestream flow. Full article

Ammonia (NH₃) has emerged as a promising carbon-free fuel for next-generation green energy systems due to its high hydrogen density, ease of storage and transport, and compatibility with existing infrastructure. These attributes contrast with hydrogen, which presents major challenges related to storage, safety, and high-pressure handling. Thus, ammonia offers a more practical alternative for combustion-based applications. However, its low reactivity and complex vaporization behavior, particularly under flash-boiling conditions, pose challenges for accurate modeling. This study presents a comprehensive numerical investigation of liquid-ammonia spray behavior under a range of ambient pressures, encompassing both flash-boiling and non-flashing conditions. Simulations were conducted using the Lagrangian particle tracking method, coupled with various turbulence models (the renormalization group (RNG) family, k-ω family, $\varsigma -f$, V2F models) to evaluate their predictive performance. Validation against experimental data for liquid and vapor penetration demonstrated that the V2F model achieved the best overall balance between accuracy and computational efficiency. Under strong flash-boiling conditions (2 bar), rapid droplet breakup and notable cooling were observed, with droplet temperatures decreasing to approximately 235 K within a few millimeters of the nozzle. In contrast, the cooling effect was more moderate under non-flashing conditions at higher ambient pressures (10–15 bar). Although the current findings were based on numerical simulations, experimental studies are ongoing to validate and refine the modeling framework further. This work provided valuable insights into the coupled effects of turbulence, phase change, and thermal transport in superheated ammonia sprays. Future research will build upon these results by extending the model to NH₃/H₂ dual-fuel systems, refining turbulence-phase interaction models, and exploring the potential application of ammonia-based flash-boiling cooling systems for electric vehicle (EV) battery thermal management. Full article

The cloud spatial uniformity in the test section is crucial for icing wind tunnels in aircraft icing research and airworthiness certification. To achieve uniform supercooled large droplet (SLD) icing conditions, both the spatial variation in droplet size distribution and the concentration should be considered. In this study, the spatial distribution of droplets under three SLD conditions is explored in the Aviation Industry Corporation of China Aerodynamics Research Institute (AVICARI)’s FL-61 icing wind tunnel. Measurements are conducted at 12 test points in vertical and horizontal directions using the holographic airborne cloud particle imager (HACPI) in conjunction with a two-axis traversing system. The droplet images obtained at specific test points below the test section centerline show deformation phenomena for droplets larger than 400 $\mathsf{\mu }$m. Additionally, the aspect ratio of deformed droplets increases with droplet size. The spatial evolution of the median volume diameter (MVD) and liquid water content (LWC) is examined. For two spray arrangements where the activated nozzles are positioned close, the test point where the LWC peak in the vertical direction occurs is higher than that of the MVD peak. Further analysis focuses on the size distribution of droplets in the vertical direction. The results show that the settling effect of the droplets larger than 50 $\mathsf{\mu }$m is evident under a flow velocity of 78 m/s. Meanwhile, the position where large droplets tend to appear lowers as the droplet size increases. Finally, the spatial uniformity of droplet size distributions at the same radial distance is discussed. Full article

Dust generated during coal mining and transportation poses serious threats to miners’ health, operational safety, and the surrounding environment. However, comprehensive review studies on dust suppression in coal mines remain limited, particularly those integrating dust movement laws with numerical simulation approaches. This review presents a systematic and reproducible analysis of dust control methods in coal mines with a particular focus on numerical simulation. Current research progress and development trends are summarized from three aspects: structural optimization of dust suppression devices, optimization of operating conditions, and ventilation system design. Existing studies indicate that structural improvements mainly concentrate on nozzle geometry, diameter, installation position, and spraying distance, while operating condition optimization primarily involves pressure regulation. Due to the complexity and high cost of full-scale experimental platforms, ventilation system optimization is largely achieved through numerical simulation, supplemented by field measurements. Studies based purely on numerical simulations remain limited in addressing the chemical modification of dust removers; however, with the advancement of molecular dynamics techniques, this area may represent a promising direction for future research. Full article

High-pressure hydrogen leakage can induce severe fire hazards and destructive overpressures. While protective walls are commonly employed as standard safety measures, most existing studies focus on either the effect of leakage height or the presence of protective walls individually. Systematic investigations on their combined influence remain limited, In contrast, the present study conducts a comprehensive analysis that explicitly considers the interaction between leakage height and the presence of protective walls, evaluating its subsequent effects on hydrogen dispersion, jet flame behavior and overpressure. A comprehensive investigation of this interaction is crucial for optimizing protective wall design and enhancing the safety of hydrogen facilities. Employing the Birch 1987 notional nozzle model, three-dimensional numerical simulations were performed to investigate the dispersion, jet flame morphology, and overpressure distribution of 35 MPa hydrogen leaks at varying heights. The results indicate that hydrogen jet flame reaches a peak temperature of approximately 2650 K within 1.1~1.2 m from the leakage orifice. Wall confinement promotes a broader accumulation of combustible gas clouds near the ground, thereby increasing the risk of delayed ignition. Low-altitude leaks generate near-ground jet flames, which bring the flame closer to the equipment and surrounding surface, potentially increasing local thermal exposure. Deterministic parametric analyses indicate that the installation of protective walls mitigates far-field overpressure by 76.5~89.5%. Crucially, as the leakage height approaches the wall height, the wall’s shielding effectiveness diminishes due to shock wave diffraction. These findings highlight that protective wall design must account for vertical leakage positioning to prevent localized safety failures. Full article

The fatigue behaviour of a 90° long radius elbow, which is adjacent to the feedwater nozzle in a BWR, was analyzed. The start-up and shutdown transients were considered. A thermo-mechanical finite element analysis was carried out to determine the stresses induced by thermal transients, considering the environmental conditions in the reactor feedwater pipe. In addition, the Palmgren–Miner methodology and the ASME B&PVC code fatigue curve were applied to evaluate the accumulated damage and service life of the component. Environmental correction factors were considered to estimate environmentally assisted fatigue. Reductions in fatigue life were observed. In the second part of this paper, a part-through thickness semielliptical crack was also postulated in the internal surface of the elbow. It was aligned along the axial direction at the crown zone. Its growth was modelled using the Paris equation, evaluating the risk of failure using fracture parameters. It was found that the vulnerable area is located on the inner surface of the elbow, due to the concentration of stress caused by the curved geometry. Failure assessment diagrams (FADs) were plotted. It was found that the crack depth is the main factor governing crack behaviour under the conditions studied. The results provide a methodology for assessing the integrity of pipes subjected to specific environmental and operating conditions. Full article