Search Results (79)

The possibility of reinforcing polymeric matrices with multifunctional fillers for improving structural and functional properties is widely exploited. The compatibility between the filler and the polymeric matrix is crucial, especially for high filler content. In this paper, polymeric matrices of Nylon 6,6 with pyrene chains were successfully synthesized to improve the compatibility with carbonaceous fillers. The compatibility was proven using graphite as a carbonaceous filler. The different properties, including thermal stability, crystallinity, morphology, and local mechanical properties, have been evaluated for various filler contents, and the results have been compared to those of synthetic Nylon 6,6 without pyrene chain terminals. XRD results highlighted that the compatibilization of the composite matrix may lead to an intercalation of the polymeric chains among the graphite layers. This phenomenon leads to the protection of the polymer from thermal degradation, as highlighted by the thermogravimetric analysis (i.e., for a filler content of 20%, the beginning degradation temperature goes from 357 °C for the non-compatibilized matrix to 401 °C for the compatibilized one and the residual at 750 °C goes from 33% to 67%, respectively. A significant improvement in the interphase properties, as proven via Atomic Force Microscopy in Harmonix mode, leads to a considerable increase in local mechanical modulus values. Specifically, the compatibilization of the matrix hosting the graphite leads to a less pronounced difference in modulus values, with more frequent reinforcements that are quantitatively similar along the sample surface. This results from a significantly improved filler distribution with respect to the composite with the non-compatibilized matrix. The present study shows how the thermoplastic/filler compatibilization can sensitively enhance thermal and mechanical properties of the thermoplastic composite, widening its potential use for various high-performance applications, such as in the transport field, e.g., for automotive components (engine parts, gears, bushings, washers), and electrical and electronics applications (heat sinks, casing for electronic devices, and insulating materials). Full article

This study introduces a novel mathematical model tailored to the unique fluid dynamics of paper-based microfluidic devices (PBMDs), focusing specifically on the transport behavior of human blood plasma, albumin, and heat. Unlike previous models that depend on generic commercial software, our custom-developed computational incorporates the Richards equation to extend Darcy’s law for more accurately capturing capillary-driven flow and thermal transport in porous paper substrates. The model’s predictions were validated through experimental data and demonstrated high accuracy in both two- and three-dimensional simulations. Key findings include new analytical expressions for uniform paper wetting after sudden geometric expansions and the discovery that plasma and albumin preferentially migrate along paper edges—a phenomenon driven by surface tension and capillary effects that varies with paper type. Additionally, heat transfer analysis indicates that a one-minute equilibration period is necessary for the reaction zone to reach ambient temperature, an important parameter for assay timing. These insights provide a deeper physical understanding of PBMD operation and establish a robust modeling tool that bridges experimental and computational approaches, offering a foundation for the optimized design of next-generation diagnostic devices for biomedical applications. Full article

This study investigates the spread patterns of tunnel fires and examines issues related to emergency response. It focuses on the temperature characteristics, spread patterns, conditions leading to multi-source fires, and the efficacy of water mist suppression methods in heavy-haul railway tunnel fires. The research employs theoretical derivations and numerical simulations to achieve its objectives. It was discovered that, during a fire in a heavy-haul railway tunnel, the temperature inside the tunnel can exceed 500 °C. Furthermore, depending on the nature of the goods transported by the train and under specific wind speed conditions, the fire source has the potential to spread to other carriages, resulting in a multi-source fire. Using the numerical simulation software Pyrosim 2022, various wind speed conditions were simulated. The results revealed that at lower wind speeds, the smoke demonstrates a reverse flow phenomenon. Concurrently, when the adjacent carriage on the leeward side of the fire is ignited, the high-temperature reverse flow smoke, along with the thermal radiation from the flames, ignites combustible materials in the adjacent carriage on the windward side of the burning carriage. Through theoretical derivation and numerical simulation, the critical wind speed for the working conditions was determined to be 2.14 m/s. It was found that while a higher wind speed can lead to a decrease in temperature, it also increases the flame deflection angle. When the wind speed exceeds 2.4 m/s, although the temperature significantly drops in a short period, the proximity of combustible materials on the leeward side of the carriage becomes a concern. At this wind speed, the flame deflection angle causes heat radiation on the leeward side, specifically between 0.5 m and 3 m, to ignite the combustible materials on the carriage surface, resulting in fire spread and multiple fire incidents. The relationship between wind speed and the angle of deflection from the fire source was determined using relevant physics principles. Additionally, the relationship between wind speed and the trajectory of water mist spraying was established. It was proposed to optimize the position of the water mist based on its deviation, and the results indicated that under critical wind speed conditions, when the water mist spraying is offset approximately 5 m towards the upwind side of the fire source, it can act more directly on the surface of the fire source. Numerical simulation results show a significant reduction in the maximum temperature and effective control of fire spread. Under critical wind speed conditions, the localized average temperature of the fire decreased by approximately 140 °C when spraying was applied, compared to the conditions without spraying, and the peak temperature decreased by about 190 °C. This modification scheme can effectively suppress the threat of fire to personnel evacuation under simulated working conditions, reflecting effective control over fires. Additionally, it provides theoretical support for the study of fire patterns in tunnels and emergency response measures. Full article

To address the hydrogeological parameters of polluted sites at the site scale, a series of physical and numerical simulation experiments were conducted to investigate seepage and solute transport under the influence of various physical fields. These experiments utilized an experimental platform designed for the acquisition of pollutant transport and transformation data, which incorporated three-dimensional multifield coupling, alongside a numerical model that also accounted for multiphysical field interactions. The numerical simulations employed Darcy’s law, the heat conduction equation, and convective–dispersive equations to analyze the seepage field, heat transfer, and solute transport processes, respectively. The findings from both physical and numerical tests indicate that variations in groundwater temperature and solute concentration significantly influence solute transport dynamics. Specifically, an increase in groundwater temperature correlates with an accelerated migration rate of sodium chloride (NaCl) solute, resulting in a reduced time for the solute to achieve equivalent concentrations in observation wells. Conversely, when the concentration of NaCl in groundwater rises, the temperature of the groundwater also increases when the solute reaches the same concentration in the observation wells. This phenomenon can be attributed to the decrease in the specific heat capacity of groundwater with higher solute concentrations. Moreover, as the concentration of sodium chloride in groundwater increases, the rate of temperature elevation in the groundwater accelerates due to a decrease in specific heat capacity associated with higher solute concentrations, thereby requiring less thermal energy for the groundwater to attain the same temperature. The results further reveal that the hydraulic conductivity of the target aquifer, specifically the pulverized clay layer, ranges from 6.72 to 8.52 × 10⁻⁶ m/s, with an effective thermal conductivity of 2.2 W/(m·K), a longitudinal dispersion of 0.554 m, and a transverse dispersion of 0.05 m. Full article

Moisture phase change (MPC), a key process in bread baking, significantly impacts heat and mass transfer, as confirmed by experiments. However, existing models poorly characterize this phenomenon, and its quantitative impact on baking needs systematic study. This research develops a coupled multiphase model for heat and mass transfer with large deformation, employing both equilibrium and nonequilibrium approaches to describe MPC in closed and open pores, respectively. Experimentally calibrated pore-opening functions and viscosity variations revealed that pore-opening primarily occurs at 71–81 °C, whereas dough solidification occurs at 50–110 °C. Model-based analysis indicates that in closed pores, evaporation–diffusion–condensation is the primary mode of moisture transport and heat transfer with contributing approximately 60% of the total effective thermal conductivity, and when pores open, water vapor evaporates or condenses on pore walls, forming an ‘evaporation front’ and ‘condensation front’. The content of liquid water increases at the ‘condensation front’ and decreases at the ‘evaporation front’. Bread deformation is predominantly governed by pressure differentials between closed pores and the ambient environment, with the partial pressure of water vapor emerging as the principal driver because its average content exceeds 70% within closed pores. These findings demonstrate that MPC governs heat and mass transfer and deformation during bread baking. Full article

Compared with traditional immunoassay methods, microfluidic immunoassay restricts the immune response in confined microchannels, significantly reducing sample consumption and improving reaction efficiency, making it worthy of widespread application. This paper proposes an exciting multi-frequency electrothermal flow (MET) technique by applying combined standing-wave and traveling-wave voltage signals with different oscillation frequencies to a three-period quadra-phase discrete electrode array, achieving rapid immunoreaction on functionalized electrode surfaces within straight microchannels, by virtue of horizontal pumping streamlines and transverse stirring vortices induced by nonlinear electrothermal convection. Under the approximation of a small temperature rise, a linear model describing the phenomenon of MET is derived. Although the time-averaged electrothermal volume force is a simple superposition of the electrostatic body force components at the two frequencies, the electro-thermal-flow field undergoes strong mutual coupling through the dual-component time-averaged Joule heat source term, further enhancing the intensity of Maxwell–Wagner smeared structural polarization and leading to mutual influence between the standing-wave electrothermal (SWET) and traveling-wave electrothermal (TWET) effects. Through thorough numerical simulation, the optimal working frequencies for SWET and TWET are determined, and the resulting synthetic MET flow field is directly utilized for microfluidic immunoassay. MET significantly promotes the binding kinetics on functionalized electrode surface by simultaneous global electrokinetic transport along channel length direction and local chaotic stirring of antigen samples near the reaction site, compared to the situation without flow activation. The MET investigated herein satisfies the requirements for early, rapid, and precise immunoassay of test samples on-site, showing great application prospects in remote areas with limited resources. Full article

This paper delves into the present situation, challenges, and possible prospects of electrical energy storage systems in the aviation industry, specifically focusing on hybrid electric aircraft and their service industries. The use of energy storage systems in the aviation industry has been the subject of a thorough literature analysis spanning the last ten years. Moreover, adapting current technological solutions from other transport sectors, such as automotive and naval, to the aviation sector presents a complex challenge, particularly when considering the typical phenomenon of thermal runaway. This study focuses on the promising behavior of lithium-based batteries among various battery technologies in the aircraft sector. Based on data gathered from completed and ongoing electric and hybrid aircraft projects, this study deals with the suitability of many different types of lithium-based batteries for use in airplanes, including lithium–sulfur, lithium–air, lithium-polymer, and lithium-ion batteries. Full article

The ambient levels of NO₂ in urban areas in China in recent years have generally shown a downward trend, but high NO₂ concentrations still exist under certain conditions, and the causes for such phenomenon and its impact on air quality remain unclear. Taking Dongying, a typical petrochemical city in the Bohai Bay of China, as an example, this paper analyzed the influence of NO₂ on urban air quality and investigated the causes for the formation of NO₂ with high concentrations. The results indicated that higher daily NO₂ concentrations (>40 μg/m³) mainly occurred during January-April and September-December each year, and higher hourly NO₂ concentrations mainly occurred during the nighttime and morning rush hour in Dongying from 2017 to 2023. With the increase in daily NO₂ concentrations, the daily air pollution levels showed a general increasing trend from 2017 to 2023. The occurrence of high NO₂ values in Dongying was affected by the combination of unfavorable meteorological conditions, local emissions and regional transports, and localized atmospheric chemical generation. High-pressure and uniform-pressure weather patterns in 2017–2022, along with land–sea breeze circulation in 2022, contribute to high NO₂ concentrations in Dongying. Boundary layer heights (BLH) in spring (−0.43) and winter (−0.36), wind direction in summer (0.21), and temperature in autumn (−0.46) are the primary meteorological factors driving NO₂-HH (High hourly NO₂ values), while BLH (−0.47) is the main cause for NO₂-HD (High daily NO₂ values). The titration reaction between NO with O₃ is the main cause for NO₂-HH in spring, summer and autumn, and photochemical reactions of aromatics have a significant influence on NO₂-HD. NOx emissions from the thermal power and petrochemical industry in Dongying and air pollution transports from western and southwestern Shandong Province (throughout the year) and from the Bohai Sea (during spring and summer) had serious adverse impact on high NO₂ values in 2022. The results of the study could help to provide a scientific basis for the control of NO₂ and the continuous improvement of air quality in Dongying and similar petrochemical cities. Full article

Nanofluids, with their enhanced thermal properties, provide innovative solutions for improving heat transfer efficiency in renewable energy systems. This study investigates a numerical simulation of bioconvective flow and heat transfer in a Williamson nanofluid over a stretching wedge, incorporating the effects of chemical reactions and hydrogen diffusion. The system also includes motile microorganisms, which induce bioconvection, a phenomenon where microorganisms’ collective motion creates a convective flow that enhances mass and heat transport processes. This mechanism is crucial for improving the distribution of nanoparticles and maintaining the stability of the nanofluid. The unique rheological behavior of Williamson fluid, extensively utilized in hydrometallurgical and chemical processing industries, significantly influences thermal and mass transport characteristics. The governing nonlinear partial differential equations (PDEs), derived from conservation laws and boundary conditions, are converted into dimensionless ordinary differential equations (ODEs) using similarity transformations. MATLAB’s bvp4c solver is employed to numerically analyze these equations. The outcomes highlight the complex interplay between fluid parameters and flow characteristics. An increase in the Williamson nanofluid parameters leads to a reduction in fluid velocity, with solutions observed for the skin friction coefficient. Higher thermophoresis and Williamson nanofluid parameters elevate the fluid temperature, enhancing heat transfer efficiency. Conversely, a larger Schmidt number boosts fluid concentration, while stronger chemical reaction effects reduce it. These results are generated by fixing parametric values as $0.1<\varpi <1.5, 0.1<\mathit{Nr}<3.0, 0.2<\mathrm{Pr}<0.5, 0.1<\mathit{Sc}<0.4, \mathrm{and} 0.1<\mathit{Pe}<1.5.$ This work provides valuable insights into the dynamics of Williamson nanofluids and their potential for thermal management in renewable energy systems. The combined impact of bioconvection, chemical reactions, and advanced rheological properties underscores the suitability of these nanofluids for applications in solar thermal, geothermal, and other energy technologies requiring precise heat and mass transfer control. This paper is also focused on their applications in solar thermal collectors, geothermal systems, and thermal energy storage, highlighting advanced experimental and computational approaches to address key challenges in renewable energy technologies. Full article

The microwave sintering of various materials is a promising technology, which has received much attention for its demonstrated potential. Both the conventional (furnace) and microwave sintering rely on thermal activation for particle bonding, for which a high temperature environment is essential. In comparison, microwave treatment achieves the same degree of densification as furnace sintering in a time shorter by a factor of two or higher and at a temperature lower by 5% to 15%. However, this is a phenomenon not yet fully understood and is commonly referred to as a non-thermal effect. Its understanding is a subject of both physics and practical interest. The non-thermal effect has been studied under years of research in order to broaden the applicability of microwave sintering. Here, we first present an overview of experimentally demonstrated advantages of microwave sintering. To facilitate further studies, we then review the literature and put together four commonly recognized interpretations of the non-thermal effects: the ponderomotive force-driven mass transport, magnetism-created cohesive forces, polarization charge-enhanced wave electric field, and polarization charge-induced attractive force among the sintered particles, with an emphasis on recent development. Full article

Sediment transport in alluvial channels has a long history of intensive research. River ice could affect sediment transport and channel morphology through the impact of various dynamic and thermal ice processes. However, studies on sediment transport under the influence of ice have been minimal until recent years. This phenomenon was partially due to the complicated interactions between ice, flow, and sediment dynamics, which require a good understanding of the river ice process, in addition to the difficult field data collection conditions. This paper reviews the progress and needs of river ice-related research on sediment transport and channel morphology, including the influence of ice cover and surface ice runs on sediment transport, the effects of frazil ice, anchor ice, and bank stability with freeze-thaw effects. Full article

For monitoring capillary moisture conduction, the most important parameter is the moisture conductivity coefficient, which is a material characteristic; however, its use in practical calculations is not very common. For further development in the field of liquid moisture propagation, an automated measuring apparatus has been developed and granted a European patent. Its essence lies in detecting the liquid water content based on a well-known physical phenomenon: electromagnetic radiation in the microwave range. The determination of the spatiotemporal moisture field is the first and fundamental step for describing transportation phenomena. The moisture field thus created allows for the viewing of the moisture conductivity coefficient, which is one of the most important parameters in describing transportation phenomena as a function of moisture. The presence of water in building materials can significantly affect their physical properties, such as mechanical or thermal–technical characteristics. This may lead to unacceptable consequences, which might only manifest after a certain period of time. In the case of multi-layered structures, moisture can transfer from one material to another. Therefore, it is essential to address this process. The advantage of the software solution described by the methodology is the use of an open communication protocol in the form of a synchronized array, which is not common in typical applications of this type. The principle of separating hardware modules is also unusual for devices of this type, as it requires the independent communication of each module with the control software. Mutual communication is handled exclusively at the software level, making it possible to modify, optimize, or parameterize the procedures as needed. Upon closer examination of the wetting curves of various materials, anomalies were revealed in some of their structures. This can be advantageously utilized in the research of newly developed composite materials. The assembled system of measuring instruments, their software integration, and control provide a foundation for the practical application of the described procedures and methods for determining the moisture field of building materials. The parameterization of individual processes, as well as the open access to data, allows for the optimization of the methodology, as materials of entirely different characteristics may require an individual approach, which will certainly contribute to the advancement of science and research in this area. Currently, this work is being followed by further extensive studies, not yet published by the authors, focusing on the application of the described moisture field to evaluate the moisture conductivity coefficient as a function dependent on the material’s mass moisture content. Their application requires specific mathematical and programming approaches due to the significant volume of data involved. Full article

The existing natural gas transportation pipelines can withstand a hydrogen content of 0 to 50%, but further research is still needed on the pathways of NO and CO production under moderate or intense low oxygen dilution (MILD) combustion within this range of hydrogen blending. In this paper, we present a computational fluid dynamics (CFD) simulation of hydrogen-doped jet flame combustion in a jet in a hot coflow (JHC) burner. We conducted an in-depth study of the mechanisms by which NO and CO are produced at different locations within hydrogen-doped flames. Additionally, we established a chemical reaction network (CRN) model specifically for the JHC burner and calculated the detailed influence of hydrogen content on the mechanisms of NO and CO formation. The findings indicate that an increase in hydrogen content leads to an expansion of the main NO production region and a contraction of the main NO consumption region within the jet flame. This phenomenon is accompanied by a decline in the sub-reaction rates associated with both the prompt route and NO-reburning pathway via CH_i=0–3 radicals, alongside an increase in N₂O and thermal NO production rates. Consequently, this results in an overall enhancement of NO production and a reduction in NO consumption. In the context of MILD combustion, CO production primarily arises from the reduction of CO₂ through the reaction CH₂(S) + CO₂ ⇔ CO + CH₂O, the introduction of hydrogen into the system exerts an inhibitory effect on this reduction reaction while simultaneously enhancing the CO oxidation reaction, OH + CO ⇔ H + CO₂, this dual influence ultimately results in a reduction of CO production. Full article

Fracture structures are important natural gas transport spaces in shale gas reservoirs, and their storage state in shale gas reservoirs seriously affects gas production and extraction efficiency. This work uses numerical modeling techniques to investigate the logging response law of the thermal and epithermal neutrons in the gas-containing fracture environment at various angles, applying neutron logging as a technical method. To increase the precision of the evaluation of the natural gas storage condition in shale gas reservoirs, the angle of the fractures’ neutron logging data is analyzed. It is found that even in an environment with the same porosity of the fractures, there are significant differences in the logging results due to the different angles of the fracture alignment: 1. the neutron counts in the high-angle (70–90°) fracture environment are 2.25 times higher than in the low-angle (0–20°), but the diffusion area of the neutrons is only 10.58% of that in the low-angle (0–20°); 2. in the neutron energy spectrum, neutron counts are spreading to the high-energy region (7–13 MeV) along with the increase in the angle of the fracture, and the feature is especially prominent in the approximately vertical (60–90°) fracture environment, which is an increase of 528.12% in comparison with the counts in the approximately horizontal angle (0–30°) environment. The main reason for these differences is the variation in the volume of the fracture within the source radiation. This volumetric difference results from the variation in fracture angles (even though the fracture porosity is the same). In view of the above phenomenon, this paper proposes the concept of “effective fracture volume”, which can intuitively reflect the degree of influence of fracture angle on neutron logging results. Further, based on the unique characteristics of shale gas reservoirs and neutrons, this paper provides important theoretical support for the modification of the porosity of the field operation, the evaluation of the physical characteristics of the gas endowment space, and the assessment. Full article

The environmental challenges associated with high-power, high-voltage electrified aircraft require a targeted approach with regard to the development of next-generation aerospace electrical insulation. This study reports findings on polyphenylsulfone (PPSU) as a matrix material based on its unique thermal, mechanical, and dielectric properties, filled with hexagonal boron nitride (h-BN) with micron- and nanoscale particulates. The inorganic ceramic filler was selected for its thermally conductive and electrically insulating performance in extreme environments. The main goal was to investigate the dielectric strength and electrical resistance (endurance) to partial discharges (PDs). Since PDs are a leading accelerated degradation phenomenon causing premature failure in organic electrical insulation, the capability of an insulating material to endure PD-induced degradation for the whole (or part of) its design life is of paramount importance. It was observed that incorporation of h-BN micro fillers can significantly improve the PD resistance, even in comparison with insulating materials typically used for electrified transportation, such as corona-resistant Kapton. It was also observed that a suitable combination of micro and nano fillers can also be used as a viable solution to increase the electrical performance and reliability of the avionics insulation components. Full article