Search Results (42)

An experimental setup has been developed that enables the conversion of a complex stream of polydisperse droplets generated by an ultrasonic dispenser into a stream of nearly identical droplets falling through a vertical channel. The fall of droplets of an aqueous NaCl solution in this channel, filled with heated dry air, is studied. Water from the droplets evaporates quickly, and crystals of a solid salt crust form on their surface. At a later stage of the process, the remaining solution is removed from the droplet using a jet of water vapor that passes through the pores of the polycrystalline crust. It was first observed that some of the drying droplets suddenly shifted to one side under the influence of the reactive force generated by the vapor jet. Images obtained using a scanning electron microscope show that the salt particles formed have a diameter of around 25 µm, are slightly porous, and consist of numerous crystals. It has been proven that these particles do not have a central cavity. The use of seawater and the role of salt particles in protecting against thermal radiation from fires are briefly discussed. Calculations based on Mie theory have shown that the contribution of light scattering by thin-walled hollow sea salt particles formed above the ocean surface during relatively slow evaporation of seawater droplets can be significant to the ocean’s heat balance. Full article

A metallic material resistant to the attack of both oxygen and sulfur at high temperatures has been desired for years. Unfortunately, commonly used commercial oxidation-resistant materials degrade rapidly in the presence of sulfur. Conversely, sulfidation-resistant metals oxidize at a rate that eliminates their practical use in oxygen-containing atmospheres. However, the latest studies in this area strongly suggest that some refractory high-entropy alloys produced by arc melting can be resistant to oxidation and sulfidation to a degree comparable to that of several traditional materials currently used in individual gas environments. Nevertheless, melting refractory metals require high temperatures and expensive equipment. To eliminate these difficulties, this work used hot pressing to fabricate the AlCrMoTaTi and AlCrNbTaTi refractory multi-component alloys, the resistance of which was tested thermogravimetrically in atmospheres containing oxygen and sulfur vapors at temperatures ranging from 800 to 1000 °C. The achieved results clearly indicate that although these alloys are not homogeneous, they exhibit high resistance. In general, both alloys react in accordance with the parabolic law, with the AlCrMoTaTi alloy exhibiting greater resistance than the AlCrNbTaTi counterpart. Consequently, these alloys can potentially be used not only as solid materials but also in coatings produced, for example, by plasma spraying. Full article

Controlling deposition parameters is fundamental to obtaining the desired properties of cathodic arc physical vapor deposition (PVD) coatings. Achieving uniform coatings on tools with complex, sharp geometries remains a significant challenge due to localized ion flux concentration. Pulsing the substrate bias is an effective way of controlling deposition energy. However, while widely used in cathodic arc PVD, the relationship between the actual bias waveform, coating integrity on sharp tool geometries, and resulting machining performance has not been systematically established. This study investigates the effect of pulsed bias duty cycle (20% to 90%) and frequency (1 to 20 kHz) on the microstructural evolution, residual stress state, and machining performance of AlTiN coated tools. Real-time oscilloscope measurements demonstrated that system inductance and capacitance significantly distort the ideal bias waveform. Microstructural analysis via Focused Ion Beam/Scanning Electron Microscopy (FIB/SEM) cross-sectioning confirmed that all bias parameters generated a dense microstructure. While pulse frequency had no significant influence on micromechanical properties or residual stress states, the duty cycle was the dominant variable. High-energy deposition (90% duty cycle) increased hardness to 33.9 GPa but generated severe compressive residual stresses (−5.2 GPa). This extreme compressive stress led to catastrophic edge delamination on sharp solid carbide endmills. Conversely, a low-energy 20% duty cycle generated a coating with lower hardness (29.4 GPa) and a near-neutral stress state (0.5 GPa), effectively preserving the edge integrity. Unlike the endmills, the turning inserts maintained their edge integrity across all deposition conditions. During the high-speed (350 m/min) dry turning of AISI 304 stainless steel, all evaluated coatings exhibited comparable tool life and cutting forces. Wear progression was characterized by rake cratering, combined with abrasion and adhesion-induced attrition on the flank. The results indicate that tool life in this extreme environment is governed primarily by high-temperature thermo-chemical stability rather than initial room-temperature hardness. Lower-energy pulsed bias deposition therefore represents a robust strategy for coating a wide range of tool geometries, delivering equivalent high-speed machining performance while preventing stress-induced delamination on sharp features. Full article

The thermal decomposition (pyrolysis) of polypropylene has been investigated as a viable method for polymer waste recycling and the production of hydrogen-rich fuel. This study examined the effects of atmosphere, temperature, and catalytic systems based on iron oxide and strontium titanate, with a focus on gas-phase composition and reaction dynamics. A reactor geometry conducive to in-bed reforming was utilized, leading to a purer gas output compared to commonly reported results, making it suitable for solid oxide fuel cell (SOFC) applications. The hydrogen concentration was enhanced with increasing temperature, primarily due to the intensified reforming of methane and higher hydrocarbons. However, only marginal improvements were observed between 700 °C and 800 °C, which limits the benefits of higher energy input. The introduction of small amounts of water vapor (approximately 3% relative humidity) resulted in a reduction in solid residue formation by approximately 50% and a slight increase in hydrogen yield. Conversely, CO₂ atmospheres suppressed hydrogen production and increased residual solids but allowed for better control over reaction dynamics. The combined strontium titanate iron oxide catalyst (S-STO@Fe_xO_γ) demonstrated high efficacy, reducing solid residues to nearly zero and producing gas mixtures containing up to 45% hydrogen. This indicates significant potential for application and further development. These findings underscore the feasibility of in-bed reforming in polypropylene pyrolysis as a waste-to-energy strategy for hydrogen-rich fuel production, warranting further optimization and investigation for SOFC integration. Full article

This study developed antimicrobial composite coatings from gelatin (GL) and carboxymethyl chitosan (CMCS) functionalized with carvacrol (CA) as a natural alternative for the preservation of strawberries. Films incorporated with 0%, 1.5%, and 3% CA were characterized by their physical, mechanical, and structural properties. The addition of CA significantly improved opacity, tensile strength, elongation-at-break, and thickness, while reducing water vapor permeability, moisture content, and solubility (p < 0.05). Spectroscopy and microscopy also confirmed CA’s uniform dispersion within the matrix. During 14 days of storage at 4 °C, strawberries coated with GL/CMCS/CA-3% significantly reduced weight loss (50.91%) and fungal contamination, improved firmness (79.31%), and maintained color and pH. Conversely, uncoated strawberries showed rapid declines in soluble solids, acidity, phenolics, anthocyanins, vitamin C, and antioxidant activity (p < 0.05). Microbial growth was effectively suppressed in coated fruits, while sensory profiles were drastically impaired in uncoated samples at the end of storage (p < 0.05). These results demonstrate that GL/CMCS/CA coatings can effectively preserve strawberry quality and extend shelf life without synthetic preservatives. Full article

As landfill mining becomes more widely applied, growing attention is being paid to the waste-to-energy conversion of landfill waste. Co-disposal of landfill waste with municipal solid waste represents one of the primary strategies for achieving energy recovery of landfill waste. In this paper, the emission characteristics of pollutants were systematically analyzed during the co-disposal of landfill waste and municipal solid waste in a full-scale municipal solid waste incineration. The study investigated the formation patterns of toxic PCDD/Fs and gaseous pollutants under different co-disposal ratios of landfill waste (0%, 15%, 25%, 35%, and 45%). In total, 136 PCDD/Fs were analyzed to investigate the influence of co-disposal ratios on PCDD/F formation in both flue gas and fly ash. The influence of varying co-disposal ratios on the phase and elemental composition of fly ash was also investigated. Co-disposal led to a significant reduction in the toxic PCDD/F concentration at the boiler outlet, mainly attributed to the higher sulfur content of LW compared to MSW. With increasing co-disposal ratios, the annual emission amounts of toxic PCDD/Fs in fly ash significantly increased. The ∑PCDD/∑PCDF ratio in both flue gas of boiler outlet and fly ash also increased, indicating an enhancement of the precursor formation pathway, while the de novo synthesis pathway was relatively suppressed. The fly ash exhibited a high proportion of highly chlorinated dioxins (degree of chlorination: 7.19–7.23), likely due to their low saturated vapor pressure. According to the Hagenmaier congener distribution, high co-disposal ratios (25–45%) suppressed the chlorination of DD/DF in fly ash but promoted the formation of gas-phase PCDFs. Different co-disposal ratios significantly influenced both the emission concentrations and removal efficiencies of air pollutants, including NOx, SO₂, and HCl. Although co-disposal did not alter the crystalline phase composition of fly ash, it led to an increased content of heavy metals such as Cu, Hg, and Pb. Full article

The direct relationship between aerosols and clouds strongly influences the effects of clouds on the global climate. Aerosol particles act as cloud condensation nuclei (CCN) and ice nuclei (IN), affecting cloud formation, microphysics, and precipitation, as well as increasing the reflection of solar radiation at the cloud tops. Processes such as gas-to-particle conversion and new particle formation (NPF) control aerosol properties that, together with meteorological conditions, regulate cloud droplet nucleation through Köhler theory and related effects. The indirect aerosol effects described by Twomey and Albrecht demonstrate how changes in aerosols impact droplet number, cloud lifetime, and precipitation efficiency. Cloud microphysical processes, including droplet growth, collision-coalescence, and solid-phase mechanisms such as riming, vapor diffusion, and aggregation, shape precipitation development in warm, cold, and mixed-phase clouds. Ice nucleation remains a significant uncertainty due to the diversity of aerosol types and nucleation modes. This work synthesizes these physical interactions to better understand how the chemical and physical properties of aerosols influence cloud and precipitation processes, supporting improvements in weather and climate prediction models despite numerical challenges arising from the complexity of aerosol–cloud interactions. Full article

Transpiration cooling that utilizes the phase change of a liquid coolant is recognized as an effective thermal protection technique for extreme environments. However, the introduction of phase change within the porous structure brings about challenges, such as vapor blockage, pressure fluctuations, and temperature inversion, which critically influence system reliability. This study conducts numerical analyses of coupled processes of heat transfer, flow, and phase change in transpiration cooling using a Two-Phase Mixture Model. The simulation incorporates a Local Thermal Non-Equilibrium approach to capture the distinct temperature fields of the solid and fluid phases, enabling accurate prediction of the thermal response within two-phase and single-phase regions. The results reveal that under low heat flux, dominant capillary action suppresses dry-out and expands the two-phase region. Conversely, high heat flux causes vaporization to overwhelm the capillary supply, forming a superheated vapor layer and constricting the two-phase zone. The analysis also explains a paradoxical pressure drop, where an initial increase in flow rate reduces pressure loss by suppressing the high-viscosity vapor phase. Furthermore, a local temperature inversion, where the fluid becomes hotter than the solid matrix, is identified and attributed to vapor counterflow and its subsequent condensation. Full article

This work presents a one-dimensional (1D) model for simulating the behavior of an FCC riser reactor processing bio-oil. The FCC riser is modeled as a plug-flow reactor, where the bio-oil feed undergoes vaporization followed by catalytic cracking reactions. The bio-oil droplets are represented using a Lagrangian framework, which accounts for their movement and evaporation within the gas-solid flow field, enabling the assessment of droplet size impact on reactor performance. The cracking reactions are modeled using a four-lumped kinetic scheme, representing the conversion of bio-oil into gasoline, kerosene, gas, and coke. The resulting set of ordinary differential equations is solved using a stiff, second- to third-order solver. The simulation results are validated against experimental data from a full-scale FCC unit, demonstrating good agreement in terms of product yields. The findings indicate that heat exchange by radiation is negligible and that the Buchanan correlation best represents the heat transfer between the droplets and the catalyst particles/gas phase. Another significant observation is that droplet size, across a wide range, does not significantly affect conversion rates due to the bio-oil’s high vaporization heat. The proposed reduced-order model provides valuable insights into optimizing FCC riser reactors for bio-oil processing while avoiding the high computational costs of 3D CFD simulations. The model can be applied across multiple applications, provided the chemical reaction mechanism is known. Compared to full models such as CFD, this approach can reduce computational costs by thousands of computing hours. Full article

Incorporating silver wires into propellant has emerged as a highly effective strategy for enhancing propellant burning rates, a technique extensively deployed in the construction of numerous fielded sounding rockets and tactical missiles. Our research, employing a multi-faceted approach encompassing thermogravimetric-differential scanning calorimetry measurements (TG-DSC), combustion diagnoses, burning rate tests, and meticulous collection of condensed combustion products, sought to elucidate how variations in silver wire quantity and winding configuration impact the combustion properties of propellants. Our findings underscore the remarkable efficacy of double tightly twisted silver wire in significantly boosting propellant burning rates under ambient conditions. Moreover, at lower temperatures, the reduced gap between the propellant and silver wire further magnifies the influence of silver wire on burning rates. However, it is noteworthy that the relationship between burning speed and combustion efficiency is not deterministic. While a smaller cone angle of the burning surface contributes to heightened burning rates, it concurrently exacerbates the polymerization effect of vapor phase aluminum particles, consequently diminishing propellant combustion efficiency. Conversely, propellants configured with sparsely twinned silver wires exhibit notable enhancements in combustion efficiency, despite a less pronounced impact on the burning rate attributed to the larger cone angle of the burning surface. Remarkably, these trends persist at lower temperatures. Based on the principle of heat transfer balance, a theoretical model for the combustion of propellants with wire inserts is developed. The reliability of this theoretical model is validated through a comparison of calculated values with experimental data. Our research outcomes carry significant implications for guiding the application and advancement of the silver wire method in solid propellants for solid rocket motors, offering valuable insights to inform future research and development endeavors in this domain. Full article

Over the last ten years, the discovery of topological materials has opened up new areas in condensed matter physics. These materials are noted for their distinctive electronic properties, unlike conventional insulators and metals. This discovery has not only spurred new research areas but also offered innovative approaches to electronic device design. A key aspect of these materials is now that transforming them into nanostructures enhances the presence of surface or edge states, which are the key components for their unique electronic properties. In this review, we focus on recent synthesis methods, including vapor–liquid–solid (VLS) growth, chemical vapor deposition (CVD), and chemical conversion techniques. Moreover, the scaling down of topological nanomaterials has revealed new electronic and magnetic properties due to quantum confinement. This review covers their synthesis methods and the outcomes of topological nanomaterials and applications, including quantum computing, spintronics, and interconnects. Finally, we address the materials and synthesis challenges that need to be resolved prior to the practical application of topological nanomaterials in advanced electronic devices. Full article

Cold quarantine storage is the practice of subjecting citrus fruit to low temperatures after harvesting to comply with stringent international phytosanitary standards for export, but fruit quality can be affected during storage. Therefore, this study investigated the effects of glycine betaine (GB) and/or methyl salicylate (MeSA) on physicochemical changes, chemical attributes of juice, and peel color of ‘Moro’ blood orange at cold quarantine storage (2 °C) for 60 days. Fruit were treated with GB (15 and 30 mM) by vacuum infiltration at 30 kPa for 8 min and vapor treatment of MeSA (100 µM) for 18 h as well as the combination of both GB concentrations with MeSA. The key findings of this research revealed that the combined treatment of 30 mM GB and 100 µM MeSA significantly mitigated weight and firmness losses in ‘Moro’ blood orange fruit during the cold quarantine period. Furthermore, there was a decrease in titratable acidity (TA) across all treatments, with the highest TA recorded for the 30 mM GB + 100 µM MeSA combination. Conversely, total soluble solids (TSS), TSS/TA ratio, and juice pH increased in all treatments, with the control treatment displaying the highest values. Regarding peel color parameters, which encompass L* (lightness), b*, hue angle (h°), chroma (C*), and a*, as well as the citrus color index (CCI), these exhibited characteristic changes during cold quarantine storage. However, the application of GB and MeSA, especially at the 30 mM GB + 100 µM MeSA level, noticeably delayed these peel color variations. Overall, GB and MeSA treatments offer significant advantages in preserving the physicochemical characteristics and chemical attributes of ‘Moro’ blood oranges during cold quarantine storage. These findings underscore the potential of GB and MeSA treatments for maintaining the quality of ‘Moro’ blood oranges during cold quarantine storage, with a noteworthy synergistic effect between MeSA and GB in preserving fruit quality. Full article

In this study, carbon-based solid acids were used to catalyze the esterification of soybean saponin-acidified oil (SSAO) with methanol vapor for the synthesis of biodiesel. The esterification conversion under different conditions was determined, and the catalyst components were determined using acid-base titration, elemental analysis, and inductively coupled plasma spectroscopy. The results showed that the conversion of SSAO under the optimal esterification conditions (i.e., catalyst loading of 6 wt%, methanol/oil molar ratio of 50:1, reaction temperature of 76 °C, and reaction time of 4 h) was 98.9%. The conversion was still higher than 80% after the catalyst was reused for four batches. The methanol vapor esterification (MVE) effectively mitigated the leaching of sulfonic acid groups and the production of sulfonate esters, while the activated white clay adsorption can significantly reduce the metal ion content in SSAO, which weakens its ion exchange with sulfonic acid groups. MVE for biodiesel synthesis is less costly compared to liquid methanol esterification because of the high recovery of methanol and the improved catalyst stability. Therefore, the addition of methanol in the form of vapor in the carbon-based solid acid-catalyzed esterification system is an effective way to maintain the catalyst activity and reduce the production cost of biodiesel. Full article

Developments in waste incineration technology in terms of efficient fuel preparation, combustion, and emissions reduction, as well as the growing needs of the community in terms of electricity, water, and air conditioning loads, are the prime motive for this study. This study presents a novel approach, in which three models of the fluidized bed combustion of municipal waste for simultaneous power generation, freshwater production, and district cooling are analyzed for their energy and exergy performance. The three simultaneously evaluated utility models are different configurations of a fluidized bed combustion system with Rankine cycle power generation, cooling with a vapor absorption refrigeration system, and fresh water production using multiple effect desalination. The output from the turbine, cooling system, and desalination system is determined using the Engineering Equations Solver for different boiler operating pressures. Energy and exergy analysis data for different pressures are used to identify the best configuration. Two variants of the absorption cooling system, namely, single effect and double effect, are considered. The variants of the multiple-effect desalination are the three-stage and five-stage methods. Input parameters used in this study are municipal solid waste generation and composition data collected for an urban community in an arid climate zone with high demand for electric power, cooling, and fresh water. Model 2, which contains two turbines with the reheating and cooling systems connected to a high-pressure turbine and water desalination connected to a low-pressure turbine, gave the best overall performance. Significant savings in terms of the replacement of conventional energy were observed from these waste conversion plants with greater benefits in arid weather conditions. The results obtained by different models under different operating criteria constitute a guideline for municipal planners for the selection of appropriate waste utilization technology, as well as the appropriate operations. Full article

In this work, the production of hydrogen from the sodium borohydride (NaBH₄) reaction was studied using an experimental bench test in a passive device operating with or without minimal external energy input. The system consists of a reactor in which a mixture based on sodium borohydride powders and an organic acid is confined. A flow of water feeds the area in which the solid mixture is confined, which undergoes a hydrolysis reaction and this generates gaseous hydrogen. The hydrogen thus produced, already saturated with water vapor, is particularly suitable for feeding polymer electrolyte fuel cells for the production of electricity because it does not require further humidification. The borohydride–organic acid coupling studied for this device, and its chemical process, provides high reaction and conversion kinetics, presenting remarkable chemical stability over time. Full article