Search Results (258)

The new technological solutions supporting hard machining processes are becoming an up-to-date research area. The enhancement of cooling lubrication efficiency in the cutting zone plays a crucial role in improving cutting performance. This paper investigates the effectiveness of Minimum Quantity Lubrication (MQL) using SiC nanoparticle-enhanced oil in the hard milling process of AISI D2 tool steel. The results are compared with dry and pure MQL modes based on criteria including cutting force components, surface roughness, tool wear, and tool life. The research results show that compared to dry and pure MQL, the SiC nanofluid MQL environment provides the best performance with reductions in feed force F_x (22.3–23.8%), thrust force F_y (20.5–55.3%), tangential force F_z (26.5–34%), surface roughness (37–62.3%), tool wear (46.1–73.3%), and increased tool life (80–200%). These findings demonstrate that the lubrication and cooling efficiency of the base oil is improved with the addition of SiC nanoparticles. The deep penetration of oil droplets into the cutting zone and the formation of the oil film significantly contributed to reducing friction and cutting heat. SiC nanoparticles not only improved the lubricating and cooling capabilities of the base cutting oil but also created secondary mechanisms within the cutting zone. Furthermore, monitoring cutting forces and surface roughness can be suggested as supplementary criteria for evaluating tool wear and tool life. This research will provide important technological guidance and a theoretical basis for the improvement of hard milling and application of the SiC nanofluid MQL technique. Full article

FeNi50 powder production for metallic magnetic cores faces challenges including low fine-powder yield and defects like hollow particles. This study employed cyclone atomization to prepare FeNi50 powder and systematically examined the effects of atomization pressure (1–6 MPa) through combined simulation, experiment, and theoretical analysis. Results show that increasing pressure reduces the average particle size (D50) from 80.7 μm to 27.9 μm and raises the fine powder yield (−500 mesh) from 19.4% to 50.0%, far exceeding that of close-coupled nozzle atomization (<10%). The powder particles are spherical/near-spherical with dense, non-hollow interiors. Higher pressure also increases the cooling rate, which blurs surface grain boundaries, refines grain structure, and induces single-crystal or amorphous characteristics in particles < 15 μm while suppressing N and O absorption. X-ray diffraction confirms the phase composition remains unchanged. These evolutions originate from three synergistic mechanisms: competition between solidification and spheroidization times, centrifugal and Magnus forces from swirling flow, and plastic-state droplet deformation imparting specific surface roughness. Cyclone atomization therefore proves a promising method for producing high-quality FeNi50 powder, suitable for large-scale manufacturing of high-performance magnetic powder cores. Full article

Hydraulic nozzles are widely utilized for dust removal, cooling, and waste heat recovery in mining production. Nevertheless, the influence of co-flow disturbance on the atomization characteristics within the downstream region of droplet fields remains inadequately understood. In this study, three typical hydraulic nozzles were selected, and the atomization characteristics of the downstream region under different co-flow disturbance intensities were experimentally investigated. The results reveal that increasing co-flow disturbance velocity does not intensify the reduction in sauter mean diameter (SMD), but markedly reduces the dispersed phase fraction (DPF). Under four co-flow disturbance velocities (1.5, 3.0, 4.5, and 6.0 m/s), the relative reduction rates of mean SMD are 6.77%, 3.27%, 4.42% and 2.60%, while those of mean DPF are 13.86%, 35.85%, 52.88%, and 61.86% (e.g., hollow-cone nozzle), respectively. The variation in SMD is achieved through the redistribution of cumulative volume among CV₁, CV₂, CV₃, and CV₄. As the velocity increases from 0 to 3 m/s, the mean SMD of the three hydraulic nozzles exhibits a decreasing trend, which can be directly attributed to the continuous increase in the total cumulative volume of CV₁ and CV₂, and the continuous decrease in those of CV₃ and CV₄. For the hollow-cone and solid square-cone nozzles, the SMD first decreases and then increases, with the turning point occurring at 3.0 m/s, consistent with the variation trend of cumulative volume fractions. In contrast, for the solid-cone nozzle, the SMD continues to decrease at velocities exceeding 3.0 m/s. This work provides both a fundamental understanding of atomization characteristics in the downstream region of hydraulic nozzles under co-flow disturbance and practical guidance for velocity control in mine spray systems. Full article

The magmatic Ni-Co-Cu mineralization in the Iken deposit in the central part of the Kun-Manie complex, Amur Oblast, Russia, hosted by an olivine-bearing websterite, is of a low-sulfide type. The fine-grained disseminations of base metal sulfides (BMS), dominantly pyrrhotite, pentlandite (a major source of Ni of industrial importance), and chalcopyrite, are followed by a scarce Pd-Pt-Ag mineralization. Elevated contents of Al in orthopyroxene (mean 2.78 wt.% Al₂O₃) along with Al–Na enrichment in clinopyroxene (diopside; mean 5.10 wt.% Al₂O₃) are associated with highly aluminous compositions of low-chromium members of the spinel–hercynite series. High levels of TiO₂ in kaersutite and titanian phlogopite also reflect a pronounced degree of fractionation of the ore-forming melt. Minor portions of sulfide melt are distributed evenly as a result of immiscibility at advanced stages of orthopyroxene crystallization, after the formation of olivine. Differentiated grains of droplet-like BMS largely settled in situ close to grain boundaries of orthopyroxene or occupied interstitial spaces of pyroxenes and olivine in association with spinel–hercynite and fluorapatite. A combination of late saturation in S with relatively quick cooling rates of the hypabyssal body prevented the effective settlement and accumulation of sulfide droplets in the ore zone. The well-developed lamellae of troilite (Fe₅₀S₅₀) exsolved from the host pyrrhotite Fe₄₈S₅₂ during subsolidus cooling, as a consequence of a low-temperature reaction triggered by a sudden drop in fO₂. An influx of mantle-derived fluid bearing CO₂, CO, and CH₄ with the rising magma could be the primary cause of the fO₂ reduction. Also, graphite-bearing metasedimentary rocks could have been assimilated. Tiny grains of minerals of noble metals (moncheite and merenskyite with essential amounts of melonite component, sperrylite, hessite, alloy Au_63.2Ag_36.8, and argentopentlandite) deposited late in a fluid-enriched medium under submagmatic conditions. Full article

The dynamic spreading behavior of droplets impacting surfaces with different wettability is a critical hydrodynamic issue in industrial applications such as inkjet printing, spray cooling, and pesticide spraying. The maximum spreading diameter coefficient (${\beta }_{max}$) is the key parameter characterizing this process. Existing theoretical models often overlook the gravitational potential energy of droplets, resulting in significant discrepancies between the calculated viscous dissipation times and experimental results, which compromises the prediction accuracy. In this study, we incorporated gravitational potential energy into the energy balance system based on the principle of system energy conservation. We introduced the Bond number (Bo) to characterize the coupling effect of gravity and surface tension. By fitting experimental data, we corrected the viscous dissipation time, obtaining $t_c$ = 3.17$d_0/v_0$, which improves the reliability of dissipated energy calculation. Using Young’s equation and the Cassie model, we derived a fourth-order ${\beta }_{max}$ prediction model that includes the Weber number (We), Reynolds number (Re), contact angle (${\theta }_c$), and Bo number. The results show that regulating the impact height and droplet diameter will affect the trend of the maximum spreading coefficient model curve: the crossover Weber numbers are 41.519 and 41.530 for different liquid viscosities under the specific experimental and modeling conditions of this study. Below these thresholds, the maximum spreading diameter coefficients are more sensitive to impact height (inertial and kinetic-energy) than to droplet diameter (volume, mass, surface energy, gravitational potential energy, Bond number). Above the critical value, the influence of droplet diameter on the maximum spreading diameter coefficient becomes more pronounced. These intersections reflect the balance between size-dependent effects and impact-inertia-related effects under specific conditions, rather than universal physical thresholds. Compared with selected classical models, the proposed model shows better consistency with experimental data and provides improved prediction for the maximum spreading coefficient of water droplets on surfaces with different wettability. This study supplements the perspective of energy analysis for the modeling of droplet impact dynamics, and can provide a basis for the theoretical optimization of spray systems and interfacial fluid control. Full article

Spray impingement cooling is a well-established heat removal technique employed across a wide range of industrial processes. A particularly significant cooling regime arises when the temperature of the cooled surface surpasses the Leidenfrost temperature of the spray. Developing an accurate numerical framework for this regime holds considerable potential for optimising industrial applications such as cryogenic machining and spray quenching. This paper presents a Eulerian–Lagrangian Conjugate Heat Transfer (CHT) model tailored for spray impingement under Leidenfrost conditions. Two heat transfer sub-models are incorporated to characterise droplet–solid thermal interaction: the first, developed by Breitenbach, is grounded in a theoretical analysis of the droplet impingement process, while the second, proposed by Deb, relies on a semi-empirical correlation. Both models were validated against an experimental correlation obtained from a literature study on orthogonal water spray impingement, yielding mean relative errors of 3.54% for the Deb model and 5.2% for the Breitenbach model across a broad range of operating conditions and surface temperatures. Full article

This study investigated the suppression effects and mechanisms of fine water mist on methane/air explosions through large-scale roadway experiments and numerical simulations. Experiments showed that fine water mist curtains deployed at 40 m and 70 m effectively mitigate flame propagation and reduce overpressure. A coupled gas–liquid numerical model was developed to reproduce flame dynamics and droplet–flow interactions. The simulations revealed droplet breakup, transport, and coupling with the evolving explosion flow field, providing mechanistic insight into gas–liquid interactions in a confined roadway. Suppression by fine water mist is primarily driven by heat absorption and cooling, while radical chain interruption plays a secondary role. These coupled mechanisms significantly reduce flame propagation velocity and pressure rise rate, achieving complete suppression under optimized configurations. This study provides a solid foundation for the design and optimization of water mist explosion suppression systems in large-scale roadways. Full article

Conventional water mist systems require high-pressure pumps and complex piping networks to generate fine water droplets, which often results in high installation costs and maintenance difficulties. Recently, a water mist system with ultrasonic waves has been proposed as a viable alternative system to address those limitations. However, there is a lack of experimental data for evaluating the fire suppression performance of water mist systems using ultrasonic waves. Therefore, in this study, a simplified water mist system with an ultrasonic wave was suggested for evaluating the fire suppression performance. Subsequently, a reduced-scale room corner test (RCT) was conducted to investigate suppression performance under various fire sizes and suppression conditions. The experimental cases were classified according to pool size, door condition, and operation of the ultrasonic water mist system. Ultimately, fire suppression performance was quantitatively evaluated using performance indices derived from fire duration and indoor temperature variation. The results demonstrate that the ultrasonic water mist system effectively suppresses fires through combined cooling and oxygen-blocking effects, while significantly reducing indoor temperature compared to oxygen-blocking suppression. The proposed performance indices enable quantitative comparison of suppression effectiveness and confirm the feasibility of ultrasonic water mist systems as an alternative to conventional high-pressure water mist systems. Full article

To address the issues of start-up over-temperature and sharp reduction in creep life caused by the lack of droplet evaporation latent heat cooling effect when adapting micro turbojet engines (MTEs) to gaseous fuels (GFs), this study optimized the start-up control strategy based on the heat accumulation effect (HAE). By establishing a 160 kgf-class MTE GF experimental platform, the nonlinear coupling mechanism between the “supply-and-burn” characteristic of GFs and the lag of rotor aero-thermodynamic response was deeply analyzed. The study found that traditional linear fuel supply strategies ignore the closed-loop energy balance under the small volume effect of the combustor, which easily causes the exhaust gas temperature (EGT) to remain above the safety threshold for a prolonged period. Unlike conventional continuous ramping strategies, this study proposes a novel open-loop multi-stage thermal relief start-up strategy. By introducing speed dwell windows in the early ignition and mid-acceleration stages, dynamic thermal relaxation intervals were constructed to achieve a “deep washout” of the accumulated thermal load. Experimental results indicate that although the optimized strategy slightly increases the instantaneous peak temperature due to the adjustment of the acceleration slope, it effectively cuts off the over-temperature time. Specifically, the over-temperature duration is reduced from 17.2 s to 11.4 s (a 33.7% reduction), and the over-temperature severity index decreases from 756.76 °C·s to 451.70 °C·s (a 40.3% reduction). This strategy successfully achieves the smooth start-up of the GF MTE, providing an efficient and reliable start-up control paradigm for the transition of micro power systems to low-carbon/zero-carbon fuels. Full article

This study investigates the transient thermo-hydrodynamic behaviour of millimetric water droplets impacting heated solid substrates under subcooled conditions. The effects of wall temperature, wall material, and impact velocity on droplet spreading, heat transfer, and cooling performance are examined using high-resolution CFD simulations, validated against in-house experimental measurements of transient temperature evolution. The results show that droplet spreading is highly affected by impact inertia, with higher velocities producing faster radial expansion and larger maximum spreading. In contrast, the thermal response is strongly influenced by substrate properties. Steel exhibits steeper temperature gradients and stronger localized cooling within the substrate, while aluminium, owing to its higher thermal diffusivity and effusivity, sustains higher total heat-transfer rates at the wall–liquid interface. Increasing wall temperature significantly enhances the absolute heat-transfer rate due to the larger thermal driving potential, although normalized temperature profiles indicate reduced relative cooling. The analysis highlights the distinct roles of hydrodynamic and thermal mechanisms: impact velocity governs the lateral distribution of cooling, whereas substrate properties control the depth-wise thermal response. These findings provide a comprehensive understanding of droplet-induced cooling from a substrate perspective and offer insights for optimizing material selection and operating conditions in spray cooling, surface quenching, and high-heat-flux thermal management applications. Full article

To address the difficulty of simultaneously achieving effective heat dissipation and adequate humidification in open-cathode air-cooled proton exchange membrane fuel cells (PEMFCs) under medium and high power operation, this study proposes a hydrothermal management strategy based on coordinated ultrasonic atomization humidification and fan speed regulation. A three-dimensional single-cell multiphysics model is developed and validated using a 300 W experimental platform. The effects of atomization frequency and water temperature on stack performance and internal hydrothermal distribution are systematically investigated. Results show that ultrasonic atomization provides inlet precooling, latent heat absorption, and active region humidification, thereby improving hydrothermal uniformity within the stack. Under the optimal condition of 100 kHz and 55 °C, the peak stack power increases by 21.0% to 319.00 W, while voltage consistency and surface temperature uniformity are also improved. Analysis based on the Stokes number and Dalton’s law of partial pressures indicates that the optimum results from a balance between suppressing droplet agglomeration and inertial deposition, and limiting oxygen dilution caused by excessive water vapor. The proposed strategy provides a compact and practical approach for improving the stability, uniformity, and efficiency of air-cooled PEMFCs. Full article

Efficient thermal management of lithium-ion batteries is critical for the safety, performance, and longevity of electric vehicles. This work numerically investigates a battery thermal management system (BTMS) for a LiFePO₄ battery, featuring a liquid-cooling plate with novel droplet-shaped turbulators and coolant with different nanofluids. Computational Fluid Dynamics (CFD) simulations were employed to analyze the effects of cooling channel geometry, nanofluid type, nanoparticle volume fraction, coolant inlet velocity, and battery discharge rate on the system’s thermal performance and pressure drop. Results show that the droplet-shaped channel reduces the maximum battery temperature by 1.64 K compared to a conventional straight channel, owing to enhanced turbulence and larger heat-transfer area. Among different coolants, the 6% Cu–water nanofluid demonstrated the highest cooling effectiveness due to its superior thermal conductivity. To balance competing objectives, a multi-objective optimization using Response Surface Methodology (RSM) and the Non-dominated Sorting Genetic Algorithm II (NSGA-II) was performed. The optimal design was achieved with a coolant velocity of 0.097 m/s and a volume fraction of Cu nanoparticle of 3.85%, which maintained the maximum battery temperature of 299.7 K with a minimal pressure drop of 26.27 Pa at a 1.03 C discharge rate. These findings highlight that a BTMS combining droplet-shaped turbulators with a Cu–water nanofluid provides a highly effective and energy-efficient thermal management strategy. Full article

Aerial forest firefighting is a critical technology for wildfire suppression. Recent studies have examined suppression agent drop dynamics, deposition patterns, and optimization strategies. This review synthesizes advances from three perspectives: (i) in-flight suppression agent jet dynamics, (ii) ground deposition patterns, and (iii) suppression effectiveness, while outlining future research directions. Flight altitude, velocity, and momentum ratio govern jet behavior—affecting penetration, expansion, and breakup. Momentum ratio, shaped by drop velocity and aircraft speed, is pivotal in penetration depth and fragmentation. Deposition patterns vary with delivery systems and flight parameters: low-altitude/low-speed drops yield higher coverage density over smaller areas, whereas high-altitude/high-speed drops cover larger areas but less densely. Suppression efficacy depends on fire intensity–vegetation interactions, droplet size–coverage requirements, and operational parameters such as response time, aircraft capacity, and real-time intelligence. Large droplets excel in cooling high-intensity flames, while fine droplets provide efficient area coverage. Adequate resources and integrated data enhance outcomes. Future work should couple multi-physics models of terrain, meteorology, and fire plume dynamics, and develop integrated deposition models including wind, thermodynamics, terrain, and fire behavior to optimize aerial dispersion in diverse wildfire scenarios. Full article

Avoiding contrails is one of the recent trends in ATM. Aviation contrails are considered a significant non-CO₂ environmental factor worth avoiding even with a CO₂ increase (lower-level cruise or horizontal avoidance, both burning more fuel). This paper is a study of the global impact of aviation on global warming considering contrails and CO₂ trade-offs. In the literature, there are two concepts on why contrails are detrimental to the environment: (i) Daytime persistent contrails have a positive effect by reflecting the Sun’s rays back, whereas the contrails persisting into nighttime need to be avoided because they block the cooling of the planet by radiation—the overall impact is negative; (ii) too much humidity is injected into the tropopause by aircraft regardless of the type of contrails, persistent or not, and even by the flights without contrails. In hypothesis (ii), contrail avoidance is not the issue, since humidity is generated by the turbine engines regardless of the visibility of the water molecules (ice crystals or water droplets). Regarding hypothesis (i), the study analysed the Earth’s reflections contributing to albedo and the Earth’s emissions at the top of the atmosphere in infrared (day and night) over 25 years (2000–2025) from CERES data and found correlations with the two pandemic years, when the number of flights was significantly reduced, to understand the real environmental impact of aviation. The conclusion is that most of the time, contrails increase the Earth’s albedo, having a positive environmental impact. The damage to the environment comes mostly from 2% of flights, mainly over Europe, and the paper puts forward some practical proposals to regulate these flights, instead of complex contrail avoidance applied at the ATM level for all flights. Full article

This study presents the development and experimental evaluation of HygroCatch, a portable hybrid fog water harvesting prototype that integrates active and passive collection mechanisms. The device operates by combining fog droplet ionization in a high-voltage direct-current (HV DC) electrostatic field, thermoelectric cooling based on the Peltier effect, and mechanical deposition of droplets on vertical rods of symmetrical triads of electrodes. This hybrid approach enables adaptive operation across a wide range of fog liquid water content (LWC) conditions. The work establishes operating parameters for stable electrostatic ionization and evaluates the contribution of thermoelectric cooling to additional water harvesting. The results indicate that an operating voltage of 13–14 kV provides a stable ionization over a broad LWC range. The average fog water harvesting rate reached 3.15 kg/m²/h, with a maximum observed value of 4.44 kg/m²/h. On average, 56% of the collected water was obtained through HV DC ionization, 25% through Peltier-based thermoelectric cooling, and 19% through mechanical deposition on electrode grids under high LWC conditions. The total electrical power consumption of the device did not exceed 38.3 Wh/kg. The results demonstrate that a hybrid fog water harvesting strategy enables stable and efficient water collection under environmental conditions in which individual passive or active methods become ineffective. Full article