Search Results (2,731)

The magnetic susceptibilities of various electrically insulating ordinary fluids depend on their local states, such as their density and temperature. When such fluids, which can be characterized as either paramagnetic or diamagnetic and occur commonly in nature, are subjected to magnetic field gradients, it induces an effective body force—the Kelvin force. This force, which depends on the susceptibility and the gradient of the square of the magnetic field strength, can become one of the effective mechanisms for modulating the flow and transport, particularly where terrestrial gravity becomes negligible, such as in free space or under microgravity conditions. For the first time, we developed a theoretical model demonstrating that a viscous current can be generated due to the contrasts between the magnetic susceptibilities of the intruding and ambient fluids in the presence of gradients in magnetic fields, analogous to the viscous gravity current in terrestrial situations. We derived similarity solutions for the two-dimensional and axisymmetric currents arising from a balance between the Kelvin buoyancy and viscous forces with a prescribed power law for the magnetic field strength. These determine the shape and various spreading relationships of the viscous current. For a prescribed time variation in the source flux, it is shown that a family of scaling laws exists for the spreading rate and the thickness of the current, which depend on the steepness of the magnetic field gradient. Unlike gravity, since the driving horizontal buoyancy arising from the Kelvin force is externally specified, it potentially offers a mechanism to control the characteristic shape and the rate of motion of the viscous current. Full article

This study investigated density-driven mixing and stratified flow dynamics in Paldang Reservoir, a river-type reservoir formed at the confluence of the South Han River, North Han River, and Gyeongan Stream in South Korea. High-resolution field observations were conducted under varying hydrologic and hydraulic conditions using an Acoustic Doppler Current Profiler (ADCP) and multi-parameter water quality sensors (EXO2). Spatial distributions of flow velocity, water temperature, and electrical conductivity (EC) were analyzed to evaluate tributary interaction and mixing behavior within the reservoir. Distinct spatial mixing structures associated with tributary inflow heterogeneity and hydraulic operation conditions were identified. During flood-season conditions, highly turbid and high-conductivity inflow from the South Han River propagated beneath the North Han River inflow, generating density-driven lower-layer intrusion near the confluence region. Under intermittent discharge conditions at the Cheongpyeong Dam, unstable upper- and lower-layer separation structures and localized reverse-flow behavior developed. In contrast, continuous discharge conditions promoted stable tributary propagation and persistent stratified mixing structures. Case-based Richardson number (Ri) estimates further indicated localized shear-driven mixing at low-Ri inflow sections and relatively stable stratification at high-Ri sections, providing quantitative support for the observed spatial heterogeneity in density-driven mixing. Overall, spatial mixing in Paldang Reservoir was governed by tributary density contrasts and further shaped by hydraulic operation conditions. These findings improve understanding of density-driven mixing processes in river-type reservoirs under varying hydraulic conditions. Full article

The study evaluated the conventional extraction (CE), microwave-assisted extraction (MAE), ultrasound-assisted extraction (UAE), and pulsed electric fields-assisted extraction (PEFAE) of bioactive compounds from orange peel waste. The effect of extraction time (0–120 min), ethanol concentration (0, 50 & 80%), and temperature (25–70 °C) were investigated, while response surface methodology (RSM) was applied for each process optimization. MAE achieved the highest total phenolic content (TPC) (6.36 mg/g w.m.) under optimized conditions (50 kJ microwave energy, 50% ethanol, 60 min), representing approximately 12% higher recovery compared to CE (TPC: 5.29 mg/g w.m.; 50 °C, 55% EtOH, 80 min). UAE (90% amplitude, 66.4 W/kg) resulted in the highest flavonoid recovery (0.48 mg/g w.m.) using 50% ethanol at 50 °C for 90 min, while PEFAE (4 kV/cm, 1000 pulses) for 75 min extraction time exhibited the same TPC yield as CE and the highest antioxidant activity (1.12 mg/g w.m.) using only water at room temperature. RSM analysis confirmed that ethanol concentration and extraction time significantly affected extraction performance. These findings demonstrate the potential of green extraction technologies for sustainable valorization of citrus processing waste and recovery of high added-value compounds. Full article

The oil-immersed environment within power transformers is characterized by high temperatures, strong electric fields, and severe electromagnetic interference, posing significant challenges for simultaneous multi-parameter monitoring. Conventional electrical sensors are susceptible to electromagnetic interference, whereas typical integrated fiber Bragg grating (FBG) sensors exhibit cross-sensitivity and reliability issues under such harsh operating conditions. To address these challenges, this paper proposes an integrated FBG-based sensor. Through specialized material and structural design, each sensing element is engineered to respond predominantly to its target parameter at the physical level. This approach effectively mitigates cross-sensitivity, enabling high-precision simultaneous measurement of oil temperature, pressure, and moisture content. Under simulated transformer oil conditions, the sensor achieved a temperature sensitivity of 17.1 pm/°C, a pressure sensitivity of approximately 4 nm/MPa, and a moisture sensitivity of 7.775 × 10⁻⁴ nm/%RS (equivalent to 6.37 × 10⁻⁴ nm/ppm at 40 °C). The results also confirmed excellent linearity, repeatability, and resistance to cross-sensitivity. These findings demonstrate that the proposed integrated FBG sensor can achieve stable multi-parameter measurement and effective decoupling under the tested transformer-oil conditions, indicating its potential for engineering application in transformer online monitoring. Full article

Thermal–gas–chemical treatment (TGCT) using activated aluminum alloys is a promising near-wellbore stimulation method for high-viscosity oil reservoirs, combining localized heat generation, hydrogen release, pressure increase, and chemical activation of the treated zone. This study evaluates the potential of TGCT for the Karazhanbas field using laboratory core flooding experiments and reservoir-scale scenario analysis. Experiments were conducted on unconsolidated core models saturated with high-viscosity oil. Treatment with activated aluminum alloy and formation water generated up to 2600 mL of gas but did not increase oil displacement efficiency. In contrast, the system containing activated aluminum alloy, 3 wt.% HCl, and 2 wt.% surfactant intensified the reaction, promoted gas–liquid foam formation, increased electrical resistivity to 5000 Ω·m, and improved oil displacement efficiency from 0.37 to 0.61. The additional oil recovery reached 16.8 mL, corresponding to a relative increase of approximately 65%. Reservoir-scale scenario calculations showed a heterogeneous production response, with maximum oil production rate increases ranging from 0.03 to 3.27 m³/day, depending on well conditions. The results indicate that TGCT efficiency is controlled by the combined thermal, gas, and chemical effects rather than gas generation alone. Field-scale implementation requires the calibration of the treatment radius, effect duration, temperature response, gas saturation, permeability alteration, and well-specific reservoir conditions. Full article

Aiming at non-uniformity in the vertical direction in the polishing effect on stainless steel after plasma electrolytic polishing (PEP), this paper took 304 L stainless steel as the research object. Under an ammonium sulfate electrolyte system with a mass fraction of 2.5 wt%, PEP was carried out utilizing different placement methods for the anode and electrolyte temperatures, and the causes of non-uniformity in the polishing process were explored. Experimental results demonstrate that the vertical polishing inhomogeneity originates from the upward movement of unruptured bubbles at the sample bottom. Under the combined effects of electrolyte internal pressure and bubble buoyancy, a vapor-gas envelope (VGE) featuring a thick upper part and thin lower part forms near the sample surface. This enhances plasma-related physicochemical reactions at the sample bottom and consequently raises the polishing rate. The vertical polishing unevenness can be alleviated by adjusting the electrolyte temperature. Non-uniformity could be improved by controlling the temperature of the electrolyte. Compared with the result at 95 °C, the maximum dimensional variation in each region on the sample at 75 °C was reduced by 36% because a VGE with more uniform thickness was formed, and a properly oxidized sparse layer helped protect the substrate from ablation and over-polishing. In addition, the removal rate of elements on the surface of stainless steel is affected by its activity due to the oxidation reaction. The high removal amount in the bottom region caused a trend of increasing Cr and decreasing Fe content percentages from the top to the bottom on the stainless-steel surface. However, the oxidation removal rate of elements is extremely fast due to the high temperature of the ionization center and strong electric field; therefore, the content percentage of each element on the surface is little changed after polishing. Full article

The present study employs an entropy analysis to investigate the boundary layer flow and heat transfer characteristics of an electrically conducting fluid subjected to the influence of a constant transverse magnetic field over a flat plate with viscous dissipation. The Keller box method is utilized to solve non-similar boundary layer equations. The effects of magnetic interaction, viscous dissipation (Eckert number), and group parameters on heat transfer, entropy generation, Bejan number, velocity, and temperature profiles are calculated. The findings demonstrate that a reduction in the magnetic parameter and Eckert number is associated with an enhancement in the heat transfer parameter. Furthermore, the surface behaves as a significant source of irreversibility due to higher entropy generation parameters near the surface. A new correlation is also obtained for the local skin friction and heat transfer parameters. An Artificial Neural Network is constructed to forecast the desired output values. Finally, the problem is mathematically defined with symbolic regression trees using genetic programming and artificial bee colony programming. The performances of the algorithms are evaluated according to coefficient of determination and root mean squared error values. The best model is obtained by ABCP algorithm with three arithmetic operators (+, -, *). The model’s coefficient of determination is found to be 0.9762, while its root mean squared error value is calculated as 0.0129. Full article

To address the limitations of existing low-temperature evaluation methods for battery electric vehicles (BEVs) in terms of real-world road adaptability, test consistency, and multidimensional performance assessment, this study proposes a standardized on-road testing and multidimensional adaptability evaluation system for BEVs in frigid environments. To address the issues that conventional bench tests cannot adequately replicate real-world road environments, routine road tests lack consistency, and existing evaluation indicators pay insufficient attention to charging efficiency and cabin heating performance, this study defines the ambient temperature for road testing, low-speed steady-state driving conditions, and the conditions for ensuring consistency in road testing. It also establishes a cold-environment adaptability evaluation system comprising three dimensions—driving range, charging efficiency, and heating, ventilation, and air conditioning (HVAC) heating performance—and four evaluation indicators: the driving range degradation rate in cold environments, charging time per 100 km, HVAC heating duration, and HVAC heating energy consumption per unit cabin volume. Field tests were conducted on 10 representative BEVs in real-world road conditions near −20 °C in Heihe City, Heilongjiang Province, China. The results indicate that the average range degradation rate for these 10 models in cold environments was 60.7%, and approximately 60% of the vehicles could complete a 100 km charge in under 30 min; the average HVAC heating time was 34 min, with an average power consumption of 9.2 kWh. The tests also revealed that the heating efficiency and thermal comfort of single-heat-pump HVAC systems at −20 °C still have room for improvement, and that the uniformity of cabin temperature distribution and consistency in foot temperature between the left and right sides significantly affect thermal comfort. The evaluation method proposed in this study can serve as a reference for testing the cold-weather adaptability of BEVs, as well as for optimizing thermal management systems and developing vehicle performance. Full article

There has been a rising trend for recovering waste heat, especially after the invention of new types of semiconductors. Among all available utilization options, thermoelectric generation (TEG) systems are promising for recovering waste heat. Thermoelectric devices are environment-friendly, operate silently, and are suitable for low- to high-power applications. This review paper presents a comprehensive study of TEGs, starting with the current problem, state of the art, advantages, disadvantages, generation and related principles, and applications, and covers different arrangements (individual and combined) and working fluids. Furthermore, this article systematically covered various experimental and numerical studies, including optimization, offering insights into heat exchanger configurations, working fluids, and performance parameters. Here, an effort is made to describe the contributions of individual/coupled TEG systems. As a coupled system, the individual TEG system is used with other systems like solar, distillation, solar pond, etc., for cogeneration and enhanced efficiency. The thermal/system parameters of individual/coupled systems are thoroughly discussed, and their impact on efficiency and power generation is illustrated. It was found that the design of the heat exchanger configuration varies from plate type to an efficient liquid-based electricity generation system in these TEG systems. The working fluid inside the fluid loop of a thermoelectric generation system varies from simple fluids to nanofluids. The current state of thermoelectric generation technology is facing challenges in module materials, equipment cost optimization, and commercialization. The progressive TEG generation capabilities have improved with recent advancements in these areas. The power densities are increasing from 0.5 to 1.2 W/cm${}^2$ in earlier standalone TEGs to 2.5–4.8 W/cm${}^2$ in recent optimized hybrid configurations, and overall system efficiencies are rising from an average of 5.2% (standalone) to 18.7% in coupled solar-TEG or waste heat recovery systems. The reported maximum ZT values are also improved from ∼1.2 to 2.1–2.8 in next-generation materials. Liquid-based heat exchangers in conjunction with nanofluids are the most efficient way to maximize temperature gradient coefficient (0.75–0.92) and minimize parasitic losses. While flexible, ionic, and hybrid next-generation material platforms are still in the early phases of development (TRL 3–5), liquid-based heat exchanger systems improved with nanofluids are closest to commercialization (Technology Readiness Level, TRL 6–8). Therefore, further research in these areas is required to mitigate these challenges. Finally, the recent developments in the thermoelectric generation field and future research direction are briefly discussed. Full article

High-power electric air heaters are key charging components in air thermal energy storage systems, but the dominant heat-loss regions and retrofit basis of existing devices remain unclear. In this study, a three-dimensional conjugate heat-transfer model was developed for an existing 1200 kW vertical electric air heater and validated using three steady-state experimental cases, with a maximum outlet-temperature deviation of 2.17%. Based on the validated model, temperature-field characteristics and segmental heat-loss distributions were analyzed under different mass flow rates. The results show that heat loss was highly non-uniform: Segments 2 and 3 accounted for 37.26% and 54.51% of the total heat loss, respectively, contributing 91.77% in total. A targeted local retrofit scheme was, therefore, proposed by filling the non-flowing inner-cylinder region in Segments 2 and 3 with glass wool and enhancing insulation near local cooling boundaries. After optimization, the average total heat loss decreased from 31.94 kW to 17.69 kW, corresponding to a 44.6% reduction. Under the rated condition, the outlet temperature increased from 1421.6 K to 1482.0 K, providing 584.8 kWh of additional effective thermal storage per cycle and an estimated payback period of 399 d. This study provides a diagnosis-guided retrofit approach for existing high-power electric air heaters. Full article

Crystallization temperature was tuned to control the crystal structure and relaxor behavior of Na_0.5Bi_5.5Ti₄AlO₁₈ films. This established a structure–property regulation pathway, enabling controlled transitions from ferroelectric, non-ergodic relaxor to ergodic relaxor states. Precise crystallization temperature control reduced grain size, thereby increasing both bulk resistivity and breakdown strength via suppressed conduction pathways. The Na_0.5Bi_5.5Ti₄AlO₁₈ film achieves outstanding energy storage performance when crystallized at 500 °C, delivering a recoverable energy density of 49.6 J/cm³ and an energy efficiency of 73.5% at an applied electric field of 2820 kV/cm. It also exhibits excellent thermal and frequency stability. Thus, crystallization temperature control is a direct, effective lever for optimizing dielectric energy storage films. Full article

To address the issues of thermal non-uniformity and insulation aging of converter transformers operating under long-term high electric field and high-temperature conditions in ultra-high-voltage direct current (UHVDC) transmission systems, this paper investigates the temperature field distribution characteristics of converter transformers based on electro–thermal–mechanical multiphysics coupling. By establishing a full-scale multiphysics simulation model of a ±800 kV converter transformer, the interactions among the electric field, temperature field, and mechanical stress field are comprehensively considered. The temperature gradient distribution and hotspot formation mechanisms within the valve-side winding and the lead-out structure are revealed. The results show that the internal temperature distribution of the converter transformer is non-uniform, resulting in a nonlinear distribution of material parameters in oil-paper insulation, which significantly affects the insulation performance. The research findings provide a theoretical basis and engineering reference for the structural optimization and thermal stability improvement of the main insulation system of converter transformers. Full article

Crack defects are prone to occur during MAG overlay remanufacturing of TBM cutter rings, thereby affecting the repair quality and service reliability of the remanufactured layer. In this study, longitudinal alternating magnetic field (LAMF) stirring was introduced into the MAG overlay remanufacturing process of H13 steel cutter rings to regulate molten-pool behavior and suppress crack defects. A molten-pool-scale sequentially coupled thermo-fluid-electromagnetic model was developed to compare the relative changes in the temperature and velocity fields with and without LAMF under identical MAG process parameters, heat-source input, material properties, and boundary conditions. In the model, the effect of LAMF was introduced through a Lorentz-force source term acting on the electrically conductive molten metal. The simulation results show that LAMF promoted heat redistribution within the molten pool, smoothed the thermal transition near the rear region of the molten pool, and reduced local heat accumulation. Meanwhile, LAMF modified the molten-pool flow pattern by weakening excessive flow along the welding direction and enhancing transverse circulation and vortex-induced mixing. Comparative overlay remanufacturing experiments were then conducted using a self-built magnetic-field stirring platform. Penetrant testing, X-ray inspection, metallographic observation, and industrial CT reconstruction were combined to characterize surface cracks, internal defects, and post-solidification microstructure. Compared with the non-LAMF condition, the maximum internal crack length decreased from 29.41 mm to 20.30 mm, corresponding to a reduction of 30.98%, and the crack-defect volume fraction decreased from 0.93% to 0.28%, corresponding to a decrease of 0.65 percentage points. The combined simulation and characterization results indicate that Lorentz-force-driven electromagnetic stirring improves the thermal-fluid conditions near the solidification front, thereby effectively reducing the formation tendency of solidification-related crack defects during MAG overlay remanufacturing. Full article

The present study investigates heat transfer characteristics in the thermally developing region of a porous tube under the local thermal nonequilibrium (LTNE) model. The influence of magnetohydrodynamic (MHD) flow on an electrically conducting fluid flowing through a porous medium under a transverse magnetic field is examined. Under the LTNE framework, two separate energy equations are employed to describe the temperature fields of the fluid and solid phases. The coupled governing equations are solved numerically using the Keller-box method. The results indicate that increasing the interphase heat transfer parameter strengthens thermal coupling between the fluid and solid phases, thereby reducing temperature differences and promoting local thermal equilibrium. In contrast, an increase in the Prandtl number reduces thermal diffusion, leading to larger temperature gradients and greater disparity between the two phases. Furthermore, the magnetic field suppresses both the velocity and temperature distributions through the Lorentz force. An increase in permeability reduces the velocity profiles due to the combined effects of the MHD and Prandtl numbers while increasing the temperature profiles. Increasing the interphase heat transfer rate drives the system from the LTNE to the LTE phase. The study confirms that LTNE effects play a significant role in thermal transfer processes in porous media and are relevant for various industrial heat transfer applications. Full article

Thermally responsive shape memory polymer materials are the most widely used type of intelligent materials and have found applications in numerous fields. However, their practical utility is often limited by poor heat conduction. Carbon nanotubes (CNTs), renowned for their exceptional thermo-conductive and photothermal properties, provide a promising solution. In this study, CNTs were integrated into polyurethane prepared by stepwise polymerization method, using hydroxyl terminated polycaprolactone (PCL-diOH), poly(ethylene glycol) (PEG) and hexamethylene diisocyanate (HDI). The resulting polyurethane composite material exhibits remarkable mechanical strength, enhanced thermal conductivity, and superior shape memory performance. Notably, it demonstrates a form of training enhancement phenomenon, which shows higher mechanical properties. And the composite could achieve stress-free two-way shape memory behavior after cyclic stretching process. Additionally, this composite material can exhibit “vitrimer” material properties at higher temperatures (110 °C), allowing for shape reprogramming. The carbon nanotube-reinforced composite material can achieve remote and precise manipulation under light stimulation. By combining the composite material with a metal thermally conductive layer, a multi-layer structure with shape memory properties can be prepared, which can achieve two-way shape memory behavior under electrical and light stimulation, further expanding the application potential of the composite material in the real world. Full article