Search Results (35)

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

The conversion of waste into a valuable product is regarded as a promising alternative to relieving the burden of solid waste management and could be beneficial to the environment and humans. This study is focused on utilizing eggshell and orange peel enriched with banana starch to fabricate biofilm via the casting technique. The developed film is further characterized by field emission scanning electron microscope (FESEM), energy dispersive X-ray spectroscopy (EDX), atomic force microscopy (AFM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). The physical properties of films, including thickness, density, color, porosity, moisture content, water solubility, water absorption, and water vapor permeability, were also characterized. The removal efficiency of the metal ions onto film at different contact times, pH, biosorbent dosages, and initial concentration of Cd(II) were analyzed using atomic absorption spectroscopy (AAS). The film’s surface was found to have a porous and rough structure with no cracks, which can enhance the target analytes interactions. EDX and XRD analyses confirmed that eggshell particles were made of calcium carbonate (CaCO₃), and the appearance of the main peak at 2θ = 29.65° and 2θ = 29.49° proves the presence of calcite in eggshells. The FTIR indicated that the films contain various functional groups, such as alkane (C-H), hydroxyl (-OH), carbonyl (C=O), carbonate (CO₃²⁻), and carboxylic acid (-COOH) that can act as biosorption materials. According to the findings, the developed film exhibits a notable enhancement in its water barrier properties, thereby leading to improved adsorption capacity. The batch experiments showed that the film obtained the maximum removal percentage at pH = 8 and 6 g of biosorbent dose. Notably, the developed film could reach sorption equilibrium within 120 min at the initial concentration of 80 mg/L and remove 99.95% of Cd(II) in the aqueous solutions. This outcome presents potential opportunities for the application of these films in the food industry as both biosorbents and packaging materials. Such utilization can significantly enhance the overall quality of food products. Full article

Properties of the Langmuir-Blodgett (LB) films of arachidic and stearic acids, versus the amount of the films’ monolayers were studied and applied for chloroform vapor detection with acoustoelectric high-frequency SAW sensors, based on an AT quartz two-port Rayleigh type SAW resonator (414 MHz) and ST-X quartz SAW delay line (157.5 MHz). Using both devices, it was confirmed that the film with 17 monolayers of stearic acid deposited on the surface of the SAW delay line at a surface pressure of 30 mN/m in the solid phase has the best sensitivity towards chloroform vapors, compared with the same films with other numbers of monolayers. For the SAW resonator sensing using slightly longer arachidic acid molecules, the optimum performance was reached with 17 LB film layers due to a sharper decrease in the Q-factor with mass loading. To understand the background of the result, Atomic Force Microscopy (AFM) in intermittent contact mode was used to study the morphology of the films, depending on the number of monolayers. The presence of the advanced morphology of the film surface with a maximal average roughness (9.3 nm) and surface area (29.7 µm²) was found only for 17-monolayer film. The effects of the chloroform vapors on the amplitude and the phase of the acoustic signal for both SAW devices at 20 °C were measured and compared with those for toluene and ethanol vapors; the largest responses were detected for chloroform vapor. For the film with an optimal number of monolayers, the largest amplitude response was measured for the resonator-based device. Conversely, the largest change in the acoustic phase produced by chloroform adsorption was measured for delay-line configuration. Finally, it was established that the gas responses for both devices coated with the LB films are completely restored 60 s after chamber cleaning with dry air. Full article

This work discusses the possibility of decomposing magnesium fluoride by ionized water vapor to form solid magnesium oxide and hydrogen gas in the reaction: MgF₂ + H₂O → MgO + 2HF. The technology and individual apparatuses of the plasma-chemical installation are described, and the influence of the fractional composition of magnesium fluoride powder on the productivity of the plasma conversion process is considered. To improve the efficiency of the plasma pyrolysis process, a method for making magnesium fluoride briquettes was developed. The completeness of the conversion process of magnesium fluoride to an oxide was evaluated by energy dispersive X-ray spectroscopy in the study of objects in scanning electron microscopy (SEM) and by X-ray diffractometry. It was found that the conversion process of magnesium fluoride to magnesium oxide has a relatively high degree of decomposition of magnesium fluoride fraction ≤75 µm. The use of the proposed processing method makes it possible to obtain pure magnesium oxide as a commercial product and to utilize fluorine-containing industrial waste. Full article

The metal transfer behavior of gas metal arc welding in a pure argon shielding gas was evaluated through experiments using a standard solid wire and a metal-cored wire. The investigation was conducted using observation techniques based on recording images by a high-speed camera equipped with laser assistance and bandpass filters in a range of welding currents. It was observed that the metal transfer mode became a streaming transfer mode when the welding current increased in the solid wire. Meanwhile, in the metal-cored wire, the droplet transfer frequency increased, and the droplet diameter decreased without changing the metal transfer mode in the globular transfer mode. We surmised that the streaming transfer in the solid wire would be caused by the spread of argon plasma at the wire tip, which decreases the effect of the electromagnetic force on droplet detachment. Conversely, due to the presence of flux inside the metal-cored wire, the argon plasma could not spread and was attached close to the iron vapor plasma at the overhead of the droplet. Hence, the electromagnetic force acting on the side of the unmelted flux was ineffective at promoting droplet detachment, preventing the transition to a streaming transfer mode. Furthermore, weld bead formation in the metal-cored wire was better than that in a conventional solid wire. Full article

Tar is an unavoidable biomass gasification byproduct. Tar formation reduces gasification efficiency and limits the further application of biomass gasification technology. Hence, efficient tar removal is a major problem to be solved in the formation and application of biomass gasification technology. Chemical looping gasification (CLG), a novel and promising gasification technology has attracted extensive attention owing to its low tar generation. Active oxygen carriers (OCs), the reduced OC in CLG, are considered to be excellent catalysts for tar cracking. In this study, the use of benzene as a typical tar model compound for tar removal using the iron ore OC is investigated. In the blank experiment, where an inert material (SiO₂) is used as the carrier, the benzene cracking is relatively low, and the benzene conversion, H₂ yield, and carbon conversion are 53.65%, 6.33%, and 1.24%, respectively. The addition of hematite promotes benzene cracking. A large amount of oxygen-containing gases (CO and CO₂) are generated. Additionally, the conversion degrees for benzene, H₂ and carbon are about 67.75%, 21.55%, and 38.39%, respectively. These results indicate that hematite performs both oxidation and catalysis during benzene cracking. The extension of the residence time facilitates benzene removal, owing to the good interaction between the gas phase and solid phase. The addition of water vapor inhibits the benzene conversion and promotes the conversion of carbon deposition. The lattice oxygen reactivity of hematite OC shows an uptrend as the cycle number is increased during the benzene conversion cycle. The experimental results confirm that CLG has a low-tar advantage and that hematite is an effective OC for benzene removal. Full article

Steel converter slag, also called Linz-Donawitz (LD) slag, has been considered as an oxygen carrier for biofuel chemical looping applications due to its high availability. In addition to its content of iron which contributes to its oxygen-carrying capacity, LD slag also contains a significant amount of calcium. Calcium, however, is known to interact with sulfur, which may affect the usability of LD slag. To get a better understanding of the interaction between sulfur and LD slag, batch scale experiments have been performed using solid and gaseous fuel with or without sulfur dioxide, together with LD slag as an oxygen carrier. The reactivity and sulfur interaction were compared to the benchmark oxygen carrier ilmenite. Sulfur increases the gasification rate of biofuel char and the conversion of CO for both LD slag and ilmenite. However, no effect of sulfur could be seen on the conversion of the model tar species benzene. The increased gasification rate of char was suspected to originate from both surface-active sulfur and gaseous sulfur, increasing the reactivity and oxygen transfer of the oxygen carrier. Sulfur was partly absorbed into the LD slag particles with calcium, forming CaS and/or CaSO₄. This, in turn, blocks the catalytic effect of CaO towards the water gas shift reaction. When the SO₂ vapor pressure was decreased, the absorbed sulfur was released as SO₂. This indicates that sulfur may be released in loop-seals or in the air reactor in a continuous process. Full article

Catalytic upgrading of vapors from pyrolysis of triglycerides materials is a promising approach to achieve better conversions of hydrocarbons and production of liquid biofuels. Catalytic cracking often shows incomplete conversion due to distillation of initial reaction products and the addition of a second catalytic reactor, whereas pyrolytic vapors are made in contact to a solid catalyst was applied to improve the physical-chemical properties and quality of bio-oil. This work investigated the effect of catalyst content and reaction time by catalytic upgrading from pyrolysis vapors of residual fat at 450 °C and 1.0 atmosphere, on the yields of reaction products, physicochemical properties (density, kinematic viscosity, refractive index, and acid value), and chemical composition of organic liquid products (OLP), over a catalyst fixed bed reactor, in semi pilot scale. Pellets of red mud chemically activated with 1.0 M HCl were used as catalysts. The thermal catalytic cracking of residual fat show OLP yields from 54.4 to 84.88 (wt.%), aqueous phase yields between 2.21 and 2.80 (wt.%), solid phase yields (coke) between 1.30 and 8.60 (wt.%), and gas yields from 11.61 to 34.22 (wt.%). The yields of OLP increases with catalyst content while those of aqueous, gaseous and solid phase decreases. For all experiments, the density, kinematic viscosity, and acid value of OLP decreases with reaction time. The GC-MS of liquid reaction products identified the presence of hydrocarbons and oxygenates. In addition, the hydrocarbon content in OLP increases with reaction time, while those of oxygenates decrease, reaching concentrations of hydrocarbons up to 95.35% (area.). The best results for the physicochemical properties and the maximum hydrocarbon content in OLP were obtained at 450 °C and 1.0 atmosphere, using a catalyst fixed bed reactor, with 5.0% (wt.) red mud pellets activated with 1.0 M HCl as catalyst. Full article