Search Results (503)

From the perspective of magnetohydrodynamics (MHD), the heat transfer properties of Maxwell fluids under MHD conditions with modified dynamic viscosity present complex challenges in numerical simulations. In this paper, we develop a time-fractional coupled model to characterize the heat transfer and MHD flow of Maxwell fluid with consideration of the Hall effect and Joule heating effect and incorporating a modified dynamic viscosity. The fractional coupled model is numerically solved based on the L1-algorithm and the spectral collocation method. We introduce a novel approach that integrates advanced algorithms with a fully discrete scheme, focusing particularly on the computational cost. Leveraging this approach, we aim to significantly enhance computational efficiency while ensuring accurate representation of the underlying physics. Through comprehensive numerical experiments, we explain the thermodynamic behavior in the MHD flow process and extensively examine the impact of various critical parameters on both MHD flow and heat transfer. We establish an analytical framework for the MHD flow and heat transfer processes, further investigate the influence of magnetic fields on heat transfer processes, and elucidate the mechanical behavior of fractional Maxwell fluids. Full article

In this paper, a coupled model is built to research the space-fractional magnetohydrodynamic (MHD) flow and heat transfer problem. The fractional coupled model is solved numerically by combining the matrix function vector products method in the temporal direction with the spectral method in the spatial direction. A fast method based on the numerical scheme is established to reduce the computational time. With the help of the Bayesian method, the space-fractional orders of the coupled model are estimated, and the problem of multi-parameter estimation in the coupled model is solved. Finally, a numerical example is carried out to verify the stability of the numerical methods and the effectiveness of the parameter estimation method. Results show that the numerical method is stable, which converges with an accuracy of O(τ2+N−r). The fast method is efficient in reducing the computational time, and the parameter estimation method can effectively estimate parameters in the space-fractional coupled model. The numerical solutions are discussed to describe the effects of several important parameters on the velocity and the temperature. Results indicate that the Lorentz force produced by the MHD flow blocks the movement of the fluid and prolongs the time for the fluid to reach a stable state. But the Hall parameter m weakens this hindrance. The Joule heating effects play a negative role in heat transfer. Full article

Thermal agents (TAs) have exhibited promise in clinical tests when utilized in cancer thermal therapy (TT). While rapid degradation of TAs may address safety concerns, it limits the thermal stability required for effective treatment. TAs, which possess exceptional thermal stability, experience gradual deterioration. There are few approaches that effectively address the trade-off between improving thermal stability and simultaneously boosting material deterioration. Here, we control the thermal character of tungsten disulfide (WS₂)-based 2D materials by utilizing an M13 phage through Joule heating (the M13–WS₂–PEG nanostructures were generated and termed a tripartite (T) nanostructure), and developed a T nanostructure-driven TT platform (we called it T-TT) for efficient thermal ablation of clinically relevant MCF-7 cells. A relative cell viability of ~59% was achieved, as well as onset time of degradation of ~0.5 week. The T-TT platform also discloses an energy density of 5.9 J/mL. Furthermore, the phage-conjugated WS₂ can be utilized to achieve ultrasound imaging for disease monitoring. Therefore, this research not only presents a thermal agent that overcomes TA limitations, but also demonstrates a practical application of WS₂-type material system in ultra-energy efficient and effective cancer therapy. Full article

This paper focuses on the multi-objective optimization of friction stir welding process parameters. Three input variables, including the axial load (AL), tool rotation speed (RS), and tool tilt angle (TA), were selected to optimize the mechanical characteristics of Al-2024 friction stir-welded (FSW) joints. The ultimate tensile strength (UTS) and impact energy (IE) were selected as output responses to measure the mechanical characteristics of Al-2024 FSW joints. A total of nine experiments, using the L9 orthogonal array as part of the Taguchi method, were performed to determine the significance of the process parameters. Gray relational analysis (GRA) was employed to conduct the multi-objective optimization of these combinations of process parameters. The results of the analysis of variance (ANOVA) showed that the AL has the most significant effect on the UTS and IE of Al-2024 FSW joints, followed by the TA and RS. The Taguchi-based GRA analysis revealed that an AL of 10 KN, a TA of 2 degrees, and an RS of 1500 rpm resulted in an optimal UTS of 333.06 MPa and an IE of 40.62 Joules. In these optimal experimental settings, optical microscopy analysis revealed the presence of a recrystallized fine-grain structure in the heat-affected zone of the welded region. Full article

The introduction of optimized nanoheaters, which function as theranostic agents integrating both diagnostic and therapeutic processes, holds significant promise in the medical field. Therefore, developing strategies for selecting and utilizing optimized plasmonic nanoheaters is crucial for the effective use of nanostructured biomedical agents. This work elucidates the use of the Joule number (Jo) as a figure of merit to identify high-performance plasmonic theranostic agents. A framework for optimizing metallic nanoparticles for heat generation was established, uncovering the size dependence of plasmonic nanoparticles optical heating. Gold nanospheres (AuNSs) with a diameter of 50 nm and gold nanorods (AuNRs) with dimensions of 41×10 nm were identified as effective nanoheaters for visible (530 nm) and infrared (808 nm) excitation. Notably, AuNRs achieve higher Jo values than AuNSs, even when accounting for the possible orientations of the nanorods. Theoretical results estimate that 41×10 nm gold nanorods have an average Joule number of 80, which is significantly higher compared to larger rods. The photothermal performance of optimal and suboptimal nanostructures was evaluated using photoacoustic imaging and photothermal therapy procedures. The photoacoustic images indicate that, despite having larger absorption cross-sections, the large nanoparticle volume of bigger particles leads to less efficient conversion of light into heat, which suggests that the use of optimized nanoparticles promotes higher contrast, benefiting photoacoustic-based procedures in diagnostic applications. The photothermal therapy procedure was performed on S180-bearing mice inoculated with 41×10 nm and 90×25 nm PEGylated AuNRs. Five minutes of laser irradiation of tumor tissue with 41×10 nm produced an approximately 9.5% greater temperature rise than using 90×25 AuNRs in the therapy trials. Optimizing metallic nanoparticles for heat generation may reduce the concentration of the nanoheaters used or decrease the light fluence for bioscience applications, paving the way for the development of more economical theranostic agents. Full article

In recent years, large power batteries have been widely used not only in automobiles and other vehicles but also in maritime vessels. The thermal uniformity of large marine battery packs significantly affects the performance, safety, and longevity of the electric ship. As a result, the thermal management of large power batteries has become a crucial technical challenge with traditional battery management system (BMS) that cannot effectively solve the battery heating problem caused by electrochemical reactions and joule heating during operation. To address this gap, a battery thermal management system (BTMS) has been newly designed. This article presents the design of a large marine battery pack, which features a liquid cooling system integrated into both the bottom and side plates of each pack. The flow plate is constructed from five independent units, each connected by manifold structures at both ends. These connections ensure the formation of a stable and cohesive flow plate assembly. Although research on the BTMS is relatively advanced, there is a notable lack of studies examining the effects of liquid temperature, flow rate, and battery discharge rate on the temperature consistency and uniformity of large marine battery packs. This work seeks to design the cooling system for the battery pack and analyzes the impact of the temperature, flow rate, and battery discharge rate of the liquid fluid on the consistency and uniformity of the battery pack temperature on the overall structure of the battery pack. It was found that, in low discharge conditions, there was good temperature consistency between the battery packs and between the different batteries within the battery pack, and the temperature difference did not exceed 1 °C. However, under high discharge rates, a C-rate of 4C, there might have been a decrease in temperature consistency; the temperature rise rate even exceeded 50% compared to when the discharge rate was low. The flow rate in the liquid flow characteristics had little effect on the temperature consistency between the batteries and the temperature uniformity on the battery surface, and the temperature fluctuation was maintained within 1 °C. Conversely, the liquid flow temperature had little effect on the temperature distribution between the batteries, but it caused discrepancies in the surface temperature of the batteries. In addition, the liquid flow temperature could cause the overall temperature of the battery to increase or decrease, which also occurs under different discharge rates. Full article

On 4 November 2021, during the rising phase of solar cycle 25, an intense geomagnetic storm (Kp = 8−) occurred. The effects of this storm on the outer magnetospheric region up to the ionospheric heights have already been examined in previous investigations. This work is focused on the analysis of the solar wind conditions before and during the geomagnetic storm, the high-latitude electrodynamics conditions, estimated through empirical models, and the response of the atmosphere in both hemispheres, based on parameters from the ECMWF ERA5 atmospheric reanalysis dataset. Our investigations are also supported by counter-test analysis and Monte Carlo tests. We find, for both hemispheres, a significant correspondence, within 1–2 days, between high-latitude electrodynamics variations and changes in the temperature, specific humidity, and meridional and zonal winds, in both the troposphere and stratosphere. The results indicate that, in the complex solar wind–atmosphere relationship, a significant role might be played by the intensification of the polar cap potential. We also study the reciprocal relation between the ionospheric Joule heating, calculated from a model, and two adiabatic invariants used in the analysis of solar wind turbulence. Full article

The hybridization of single-walled carbon nanotubes (SWCNTs) and Cu nanoparticles offers a promising strategy for creating highly conductive and mechanically stable fillers for flexible printed electronics. In this study, we report the ultrafast synthesis of SWCNT/Cu hybrid nanostructures and the fabrication of flexible electrodes under ambient conditions through a laser-induced photo-thermal reaction. Thermal energy generated from the nonradiative relaxation of the π-plasmon resonance of SWCNTs was utilized to reduce the Cu-complex (known as a metal–organic decomposition ink) into Cu nanoparticles. We systematically investigated the effects of SWCNT concentration and output laser power on the structural and electrical properties of the SWCNT/Cu hybrid electrodes. The SWCNT/Cu electrodes achieved a minimum electrical resistivity of 46 μohm·cm, comparable to that of the metal-based printed electrodes. Mechanical bending tests demonstrated that the SWCNT/Cu electrodes were highly stable and durable, with no significant deformation observed even after 1000 bending cycles. Additionally, the electrodes showed rapid temperature increases and stable Joule heating performance, reaching temperatures of nearly 80 °C at an applied voltage of less than 3.5 V. Full article

Hot-spot generation is critical to the performance and lifespan of photovoltaic (PV) modules; however, the underlying mechanisms of hot-spot formation have not been fully elucidated. This work conducted a localized shading test on a PV module, measured the micro-electrical characteristics and temperature distributions of both the shaded and unshaded cells, calculated the heat-source power densities, and then predicted the occurrence and locations of hot and cold spots via numerical simulations. It was found that, under an irradiance of 750 W/m², when one cell in a PV module is shaded by 1/2, the unshaded area within the shaded cell exhibited a hot spot, with the temperature reaching up to 77.66 °C, approximately 22.5 °C higher than the surrounding cells. The intrinsic mechanism for the occurrence of the hot spot is that, compared with the unshaded cells, the unshaded portion of the shaded cell can generate an extra significantly large Joule heat power density, about 1079.62 W/m². The reason for generating such a large Joule heat power density is that this portion is in a reverse-bias state with a high current density flowing through it, according to our measurements. In contrast, the shaded portion forms a cold spot, about 7.5 °C cooler than the surrounding cells. This is because the shaded portion can only generate a Joule heat power density of about 46.98 W/m² due to the small reverse-bias current density flowing through it and fails to absorb heat from solar irradiance, which is about 645 W/m². Moreover, this work demonstrates that the hot-spot temperature initially rises and then decreases with increasing shading ratio, with the highest temperatures and the most pronounced temperature changes occurring around a shading ratio of 1/2. The presented method can be also used to evaluate the performance and reliability of various other PV modules under local shading conditions. Full article

The trend in partial pressure of atmospheric CO₂, P(CO₂), across the 66 MYr of the Cenozoic requires elucidation and explanation. The Null Hypothesis sets sea surface temperature (SST) as the baseline driver for Cenozoic P(CO₂). The crystallization and cooling of flood basalt magmas is proposed to have heated the ocean, producing the Paleocene–Eocene Thermal Maximum (PETM). Heat of fusion and heat capacity were used to calculate flood basalt magmatic Joule heating of the ocean. Each 1 million km³ of oceanic flood basaltic magma liberates ~5.4 × 10²⁴ J, able to heat the global ocean by ~0.97 °C. Henry’s Law for CO₂ plus seawater (H_S) was calculated using δ¹⁸O proxy-estimated Cenozoic SSTs. H_S closely parallels Cenozoic SST and predicts the gas solute partition across the sea surface. The fractional change of Henry’s Law constants, Hn−HiHn−H0 is proportional to ΔP(CO₂)_i, and Hn−HiHn−H0×∆P(CO2)+P(CO2)min, where ΔP(CO₂) = P(CO₂)_max − P(CO₂)_min, closely reconstructs the proxy estimate of Cenozoic P(CO₂) and is most consistent with a 35 °C PETM ocean. Disparities are assigned to carbonate drawdown and organic carbon sedimentation. The Null Hypothesis recovers the glacial/interglacial P(CO₂) over the VOSTOK 420 ka ice core record, including the rise to the Holocene. The success of the Null Hypothesis implies that P(CO₂) has been a molecular spectator of the Cenozoic climate. A generalizing conclusion is that the notion of atmospheric CO₂ as the predominant driver of Cenozoic global surface temperature should be set aside. Full article

The conversion of nitrogen (N₂) and water (H₂O) into NH₃ by photocatalysis under ambient conditions has been considered an environmentally friendly strategy. However, developing effective catalysts for N₂ fixation is still challenging. Herein, we report a bimetallic JH Fe, Co/TiO₂ derived from NH₂-MIL-125(Ti) by the fast Joule heating (FJH) method for visible–light–driven catalytic N₂ fixation. It was found that the photocatalytic N₂ reduction efficiency of bimetallic FC@TiO₂-JH was improved, enabling an NH₃ yield rate of 110.14 µmol g⁻¹ h⁻¹ without any sacrificial agents. Furthermore, the rate was higher than those of Fe@TiO₂-JH and Co@TiO₂-JH, suggesting that the synergistic effect between Fe and Co broke the electronic equilibrium and increased the center of its d-band, enhancing electronic feedback to the antibonding π* orbitals of N₂ while weakening the bonding energy of N≡N. Meanwhile, the rate was about 2.75 times higher than that of FC@TiO₂-TF, which was calcined in a tube furnace. It is assumed that FJH might lead to the formation of lattice defects, leading to localized charge deficiency, enhanced carrier separation, and transport. Thus, doping of Fe and Co synergistically interacted with the defects produced from FJH, facilitating the photocatalytic reduction process. As detected, it had a greater ability to separate hole–electron pairs and transferred electrons to adsorbed N₂ at faster rates. Our work demonstrates a prospective strategy for designing bimetallic catalysts derived from NH₂-MIL-125(Ti) for N₂ fixation. Full article

Electro-conductive films with excellent flexibility and thermal behavior have great potential in the fields of wearable electronics, artificial muscle, and soft robotics. Herein, we report a super-elastic and electro-conductive composite film with a sandwich structure. The composite film was constructed by spraying Polyvinyl alcohol (PVA) polymers onto a buckled conductive carbon nanotube-polydimethylsiloxane (CNTs-PDMS) composite film. In this system, the PVA and PDMS provide water sensing and stretchability, while the coiled CNT film offers sufficient conductivity. Notably, the composite film possesses high stretchability (205%), exceptional compression sensing ability, humility sensing ability, and remarkable electrical stability under various deformations. The produced CNT composite film exhibited deformation (bending/twisting) and high electro-heating performance (108 °C) at a low driving voltage of 2 V. The developed CNT composite film, together with its exceptional sensing and electrothermal performance, provides the material with promising prospects for practical applications in wearable electronics. Full article

African scientific research faces formidable challenges, particularly with limited access to state-of-the-art measurement instruments. The high cost associated with these devices presents a significant barrier for regional research laboratories, impeding their ability to conduct sophisticated experiments and gather precise data. This predicament not only hampers the individual laboratories but also has broader implications for the African scientific community and the advancement of knowledge in developing nations—the financial cost barrier considerably impacts the research quality of these laboratories. Reflection on technical and economical solutions needs to be quickly found to help these countries advance their research. In civil engineering, the thermal conductivity property is the most important measurement for characterizing heat transfer in construction materials. Existing devices (i.e., conductometers) in a laboratory are expensive (approximately EUR 30,000) and unavailable for some African laboratories. This study proposes a new and affordable device to evaluate thermal conductivity in construction materials. The method involves establishing a thermal flux between a heat source (from the Joule effect provided by steel wool where a current is circulating) and a cold source (generated by ice cubes) under steady-state conditions. The development of the cylindrical prototype is based on the comparative flux-meter method outlined in the measuring protocol of the ASTM E1225 standard document. Experiments were conducted on four distinct materials (polystyrene, wood, agglomerated wood, and rigid foam). The results indicate a correct correlation between the experimental values obtained from the newly developed prototype and the reference values found in the literature. For example, concerning the experimental polystyrene study, the detailed case analysis reveals a good correlation, with a deviation of only 4.88%. The percent error found falls within the acceptable range indicated by the standard recommendations of the ASTM E1225 standard, i.e., within 5% acceptable error. Full article

This work explores microcombustion technologies enhanced by plasma-assisted combustion, focusing on a novel simulation model for a Y-shaped device with a non-premixed hydrogen-air mixture. The simulation integrates the ZDPlasKin toolbox to determine plasma-produced species concentrations to Particle-In-Cell with Monte Carlo Collision analysis for momentum and power density effects. The study details an FE-DBD plasma actuator operating under a sinusoidal voltage from 150 to 325 V peak-to-peak and a 162.5 V DC bias. At potentials below 250 V, no hydrogen dissociation occurs. The equivalence ratio fitting curve for radical species is incorporated into the plasma domain, ensuring local composition accuracy. Among the main radical species produced, H reaches a maximum mass fraction of 8% and OH reaches 1%. For an equivalence ratio of 0.5, the maximum temperature reached 2238 K due to kinetic and joule heating contributions. With plasma actuation with radicals in play, the temperature increased to 2832 K, and with complete plasma actuation, it further rose to 2918.45 K. Without plasma actuation, the temperature remained at 300 K, reflecting ambient conditions and no combustion phenomena. At lower equivalence ratios, temperatures in the plasma area consistently remained around 2900 K. With reduced thermal power, the flame region decreased, and at Φ = 0.1, the hot region was confined primarily to the plasma area, indicating a potential blow-off limit. The model aligns with experimental data and introduces relevant functionalities for modeling plasma interactions within microcombustors, providing a foundation for future validation and numerical models in plasma-assisted microcombustion applications. Full article

Developing multifunctional flexible composites with high-performance electromagnetic interference (EMI) shielding, thermal management, and sensing capacity is urgently required but challenging for next-generation smart electronic devices. Herein, novel nacre-like aramid nanofibers (ANFs)-based composite films with an anisotropic layered microstructure were prepared via vacuum-assisted filtration and hot-pressing. The formed 3D conductive skeleton enabled fast electron and phonon transport pathways in the composite films. As a result, the composite films showed a high electrical conductivity of 71.53 S/cm and an outstanding thermal conductivity of 6.4 W/m·K when the mass ratio of ANFs to MXene/AgNWs was 10:8. The excellent electrical properties and multi-layered structure endowed the composite films with superior EMI shielding performance and remarkable Joule heating performance, with a surface temperature of 78.3 °C at a voltage of 2.5 V. Additionally, it was found that the composite films also exhibited excellent mechanical properties and outstanding flame resistance. Moreover, the composite films could be further designed as strain sensors, which show great promise in monitoring real-time signals for human motion. These satisfactory results may open up a new opportunity for EMI shielding, thermal management, and sensing applications in wearable electronic devices. Full article