Search Results (4,134)

Cellulose paper, a natural polymeric dielectric, determines the lifetime of oil–paper insulation systems in transformers, yet its molecular degradation behavior in ester-based insulating media remains insufficiently clarified. This study investigates the electro–thermal aging of cellulose polymer immersed in soybean-based natural ester (SBNE) and palm fatty acid ester (PFAE), with emphasis on depolymerization and its relationship with partial discharge (PD) activity. Accelerated aging experiments were conducted under combined electrical and thermal stress, and the evolution of the degree of polymerization (DP) was measured to quantify polymer chain scission. Phase-resolved PD (PRPD) patterns were recorded during aging, and multi-dimensional statistical features were extracted and reduced using principal component analysis to characterize degradation-sensitive electrical responses. The results show a progressive decrease in DP with aging time in both ester media, accompanied by distinct PD evolution characteristics, indicating different influences of the two esters on cellulose polymer stability. An ensemble learning model integrating multiple classifiers was further employed to identify aging stages based on PD features, achieving reliable discrimination performance. These findings establish a correlation between cellulose depolymerization and dielectric discharge behavior, providing a polymer-centered interpretation of aging mechanisms in ester-based oil–paper insulation systems. Full article

Thermoplastic composite resistance welding boasts stable process, low cost and reliable quality, making it a dependable joining technique for such materials. This process employs a heating element (HE) as the sole heat source and therefore, it is critical in controlling the welding process. This study proposed a perforated stainless-steel mesh (SSM) as the HE and investigated the effect of welding parameters and insulation film thickness on the joint performance of resistance welded carbon-fiber-reinforced polyamide 6 (CF/PA6). The results showed that the joint lap shear strength (LSS) increased first then decreased as the welding pressure, welding time and welding current increased. The maximum LSS reached 24.4 MPa when 0.2-mm-thick films were used. The joint failure mode was identified as blocky fiber peeling with compromised fiber continuity for the joints welded with 0.1-mm-thick and 0.3 mm-thick PA6 films. For the joints made with 0.2-mm-thick PA6 films, the joint failure mode was characterized by resin peeling from the fiber surface. Full article

To overcome the low thermal conductivity and flow channel clogging inherent in traditional phase change materials (PCMs) for immersion cooling, this study develops a novel oil-based phase change emulsion (PCE) integrating high thermal transport with adaptive rheological behavior. A liquid thermal conductivity enhancer was synthesized by modifying epoxidized soybean oil with LiTFSI and blending it with a synthetic ester to form a dielectric base fluid. A mid-to-low-temperature PCM (Span65) was then incorporated via surfactant-free ultrasonic emulsification. The resulting PCE exhibits a tunable phase-change window (25~40 °C) driven by interfacial confinement effects and a multiscale lamellar network. It achieves significantly enhanced thermal conductivity (15% increase over base oil) while maintaining excellent electrical insulation (<10⁻⁹ S/cm). Rheologically, the emulsion transitions from shear-thinning in the solid state to near-Newtonian in the liquid state, optimizing both suspension stability and pumping efficiency. This work establishes a strategy for designing high-performance, safe, and energy-efficient dielectric coolants, offering a robust solution for next-generation electronic and battery thermal management systems. Full article

The retrofit of existing residential buildings plays a critical role in reducing energy consumption and carbon emissions in the building sector. However, previous retrofit evaluations often fail to account for the age-related thermal and lighting requirements of residents in aging residential buildings, thereby overlooking the substantial behavioral heterogeneity that shapes retrofit effectiveness. This study evaluates the comprehensive performance of different building envelope retrofit strategies, considering occupants’ thermal and visual comfort, from the perspectives of energy efficiency, economic feasibility, and environmental sustainability. First, age-specific differences in occupancy patterns, thermal preferences, and lighting requirements between elderly and non-elderly comparison group occupants were systematically extracted from the literature. Then, a typical high-rise residential building was modeled in EnergyPlus to serve as the reference building, within which the differentiated occupant behavior models were implemented, and the pre-retrofit condition was defined as the baseline scenario. Next, six commonly applied exterior wall insulation materials and different glass configurations and window frames were parameterized and evaluated under varying insulation thicknesses and remaining building service life scenarios. Finally, the energy-saving performance, economic benefits, and carbon reduction potential of envelope retrofit measures were quantitatively assessed across three primary functional zones (bedroom, living room, and study), using area-normalized indicators. The results indicate that, in the retrofit of existing residential buildings, bedrooms and study rooms exhibit greater retrofit benefits than living rooms, primarily due to longer occupancy durations and higher heating demand. In terms of retrofit strategies, exterior wall insulation consistently outperforms window retrofitting in energy-saving potential, with energy-saving rates of approximately 3.2–4.3% depending on functional zone, material type, and insulation thickness. Among the evaluated materials, vitrified microbead insulation performs best overall in terms of energy, economic, and carbon benefits at 40–60 mm thickness. These findings support occupant-informed, low-carbon retrofit decision-making for existing residential buildings. Full article

During high-speed flight, intense friction on the aircraft surface always occurs due to atmospheric fluid medium. The resultant high frictional drag will trigger a significant aerothermal effect, and thus raise the surface temperature sharply to 1000–3000 °C. This extreme heat not only remarkably reduces the aerodynamic efficiency but probably also causes thermal failure of the structural integrity and damage of internal components. Therefore, robust heat-resistant materials are the preferred choice for designing high-speed aircraft due to their benign tolerance to high temperature, oxidation and ablation as well as large strength and durability. This work systematically unveils the generation mechanism of frictional drag in high-speed flight and introduces the characteristics and applications of typical thermal insulation materials (TIMs). After that, the recent progress in a thermally protected material system including metal-based alloys and metal-doped compound materials, ultra-high-temperature ceramics (UHTCs), carbon (C)/carbon (C) and C/SiC composites, ceramic matrix composites (CMCs), UHTCs-modified C/C and C/SiC composites is conducted. Finally, the current technical bottlenecks are discussed, simultaneously proposing the development direction of novel TIMs for the potential applications for high-speed aircrafts. Full article

Thermal barrier materials play a crucial role in reducing heat transfer, suppressing thermal runaway (TR) propagation, and mitigating the risk of fire and explosion. Among the various types of thermal barrier materials, polymer-based thermal barrier materials, including polyimide (PI), aramid, epoxy resin (ER), polyurethane (PU), phenolic resin (PR), and silicone, have been widely applied in lithium-ion battery (LIB) safety protection owing to their excellent thermal stability, structural tunability, and favorable processability. This review provides a systematic and comprehensive overview of polymer-based thermal barrier materials for mitigating thermal runaway propagation in LIBs. The propagation pathways of TR in battery systems are first outlined to clarify the functional requirements of thermal barrier materials. Subsequently, representative classes of polymer materials are reviewed with emphasis on their structural characteristics and advantages. Strategies for enhancing thermal insulation, flame retardancy, heat absorption capacity, and mechanical robustness are then summarized in the context of thermal safety protection. Finally, key challenges associated with polymer-based thermal barrier materials are discussed, and future development directions are proposed. Full article

The thermal conductivity of thermal insulation materials is a critical parameter for assessing energy efficiency and performance in building, industrial, and aerospace applications. This study combined numerical simulation, parameter inversion optimization and experimental measurement to evaluate the transient hot-wire method for measuring the thermal conductivity of expanded polystyrene (EPS) foam. Using a nickel wire as the hot wire, the effects of various parameters—including wire length and width, heating power, Kapton film thickness and end effect—were systematically analyzed through finite element analysis and Bayesian optimization algorithm. Following the simulation and inversion conclusions, a series of hot-wire sensors with a fixed length of 30 mm and widths of 25 μm, 50 μm, 100 μm, 150 μm, and 200 μm were fabricated for experimental validation. Measurement results were compared against a reference value obtained by the guarded hot plate method. It was found that the sensor with a length of 30 mm and a width of 100 μm demonstrated optimal performance among the configurations tested, with deviations between the experimental measurements and the reference value remaining within approximately ±1.5%. Full article

The present theoretical study proposes and unravels chemical graft modification using a novel voltage stabilizer (3-amino-5-chlorophenyl 3-fluorophenyl methanone, ACFM) to ameliorate electrical insulation performance, oxygen-resistant characteristics, and thermal stability of addition-cure silicone rubber (SiR) used for cable accessory insulation in power transmission systems. First-principles calculations demonstrate that chemically grafted ACFM introduces shallow hole and electron traps into addition-cure SiR macromolecules to respectively impede hole transport and restrict hot electron production. Through molecular dynamics and Monte Carlo simulation, the chemically grafted ACFM is verified to enhance chain segment coalescence and decrease oxygen compatibility of addition-cure SiR macromolecules due to its higher dipole moment, leading to a reduction in oxygen permeation and improvement in thermal stability of the SiR crosslinked material. It is indicated from first-principles oxidation reaction paths that chemical grafting ACFM contributes positively to the oxidative stability of addition-cure SiR. The improved abilities of charge trapping and withstanding high temperatures together with enhanced resistance to both oxygen infiltration and oxidation of the addition-cure SiR material, as unraveled on a molecular scale in this research, open an avenue for developing advanced polymer dielectrics applied in harsh environments. Full article

Olive pomace biochar, obtained through the pyrolysis of lignocellulosic biomass, has emerged as a sustainable and multifunctional additive for polymer composites. Its physicochemical properties, including porosity, surface area, and electrical conductivity, can be tailored by controlling feedstock type and pyrolysis conditions. Although mechanical reinforcement and thermal stability improvements are well documented, the influence of biochar on surface-related properties such as wettability and contact angle remains insufficiently explored for environmentally relevant composite systems. In this study, epoxy-based composites containing biochar synthesized at 750 °C were evaluated in terms of their water interaction behavior by monitoring the evaporation dynamics of ultra-pure water droplets (10 μL, 0.055 mS/cm conductivity) at eight time intervals between 20 and 580 s using high-resolution digital microscopy. Image enhancement and segmentation were performed prior to Discrete Cosine Transform (DCT) analysis to describe droplet geometry in the frequency domain. Time-dependent variations in the standard deviations of DCT coefficients were optimized using the Bat Algorithm, resulting in mathematical models capable of accurately representing droplet evolution and surface–fluid interactions. The primary novelty of this study lies in the development of a hybrid experimental–computational framework that integrates droplet-based wettability measurements with signal-domain analysis and metaheuristic optimization. Unlike conventional studies focusing solely on material characterization, this approach establishes quantitative relationships between surface behavior and numerical descriptors derived from DCT and the Bat Algorithm. The proposed methodology provides a data-driven tool for predicting wettability trends in biochar-reinforced composites and supports the development of moisture-resistant materials for coatings, packaging, and thermal insulation applications within the context of sustainable composite design. Full article

In the context of the “dual-carbon” targets and the development of green building materials, lightweight mortar has attracted considerable attention, owing to its low density and excellent thermal insulation properties. However, lightweight aggregates, such as vitrified microspheres, while effectively reducing mortar density, exhibit high porosity and weak interfacial bonding, which compromise mechanical performance. To address this issue, this study introduces sugarcane bagasse fiber (SBF) as a reinforcing material, with contents of 0%, 0.4%, 0.8%, 1.2%, and 1.6%. The effects of SBF on physical properties (consistency, density, water absorption) and mechanical properties (compressive strength, flexural strength, and tensile bond strength) were systematically evaluated. Furthermore, low-field nuclear magnetic resonance (LF-NMR) and scanning electron microscopy (SEM) were employed to analyze pore structure and interfacial transition zone (ITZ) characteristics at multiple scales. The results indicate that: (1) at low contents (0.4–0.8%), SBF was uniformly dispersed, improving matrix compactness; (2) compared with the control group, the 28-day compressive, flexural, and tensile bond strengths increased by 7.1%, 13.1%, and 25%, respectively; (3) NMR analysis revealed that the incorporation of SBF significantly increased the proportion of capillary pores, reduced total porosity, and enhanced mortar compactness, thereby improving mechanical strength; (4) fractal dimension analysis showed that contents of 0.4% and 0.8% increased structural complexity while reducing pore connectivity, leading to higher compressive strength; (5) SEM observations further demonstrated that the fibers provided bridging and anchoring effects within the ITZ, promoted the deposition of hydration products, and enhanced interfacial compactness. Full article

This study takes the relevant literature published in the past decade as the research object, screens the literature by setting clear inclusion and exclusion criteria, and systematically reviews the thermal insulation performance, durability, and prospects for engineering applications of bio-based thermal insulation materials by means of qualitative integration and comparative analysis. With the advantages of low energy consumption, renewability, and biodegradability, bio-based thermal insulation materials have emerged as a green alternative to traditional thermal insulation materials. This paper systematically reviews the research progress of such materials, which are classified into two categories: natural biomass (e.g., straw bales and cork boards) and bio-based composites. The core thermal insulation indicators include thermal conductivity, thermal resistance, and thermal storage coefficient, and the performance is affected by factors such as component ratio, pore structure, temperature, and humidity. The thermal conductivity of some bio-based materials is comparable to that of expanded polystyrene (EPS) and mineral wool. In terms of durability, temperature–humidity cycling, corrosion, biological erosion, and mechanical action are the main causes of performance degradation, and composite modification can effectively improve their stability. Current engineering applications face challenges such as thermal insulation performance being susceptible to humidity, poor construction compatibility, high costs, and a lack of relevant standards. Future research should focus on the development of high-performance composite systems, the investigation of long-term durability mechanisms, the innovation of low-cost green preparation technologies, and the establishment of unified standards, so as to promote the large-scale application of bio-based thermal insulation materials in the construction industry and contribute to the achievement of carbon neutrality goals. Full article

This study investigates the sound insulation performance of an anechoic chamber, exploring the influence patterns of different multilayer material combinations on wall sound insulation characteristics. Based on sound transmission theory, a predictive model for multilayer material wall sound insulation was established. The finite element method was employed to simulate the sound propagation characteristics of walls and glass doors with various material combinations. After validating the simulation results through a double-room method experiment, the material combination scheme for the anechoic chamber walls and glass doors was optimized. Based on this, a 1000 mm × 1000 mm × 2300 mm soundproof room prototype was designed and constructed. Its sound insulation performance under reverberant conditions was tested using the insertion loss method and compared with simulation data. Simultaneously, a hybrid calculation method combining low-frequency finite element analysis with high-frequency statistical energy analysis enabled precise and efficient prediction of the overall sound insulation performance of the soundproof room. Research revealed that single-pane glass with thicknesses between 5 and 20 mm conformed to the mass law, with sound insulation increasing by an average of 0.8 dB per additional millimeter. The 10 mm single-pane glass emerged as the optimal choice for the soundproof room’s glass door due to its ideal thickness and excellent low-to-mid-frequency sound insulation. The optimized wall structure featured compact thickness, outstanding low-frequency sound insulation, and balanced mid-to-high-frequency performance. Simulation and experimental results for the core frequency range of 63–1000 Hz showed high consistency, which validates the reliability of the theoretical model and simulation methodology within this frequency band. The deviation of simulation results from experimental data in the frequency range above 1000 Hz is mainly caused by acoustic leakage due to experimental sealing defects, and the high-frequency simulation results are only used for trend analysis rather than conclusion support. This study identifies the optimal multi-layer material combination for soundproof rooms, providing practical material strategies for acoustic design. It also reveals the sound insulation mechanisms of multi-layer composite structures. The findings offer significant reference for optimizing soundproofing materials and structures in architectural acoustics and transportation noise control. Full article

Crosslinked polyethylene (XLPE) is a widely used cable insulation material for power cables at various voltage levels, offering excellent electrical, mechanical, and thermal stability. However, during the continuous extrusion moulding process, prolonged shear action and localized temperature accumulation can easily induce premature crosslinking. This leads to a decline in melt rheological properties and reduced processing stability, as well as having an adverse effect on the microstructure and overall performance of the formed insulation layer. This study systematically investigated the impact of shear-induced pre-crosslinking on the mechanical properties and dielectric characteristics of XLPE cable insulation materials through experimental testing methods. The experimental results demonstrate that, while premature crosslinking has a minimal effect on mechanical properties, it significantly deteriorates dielectric performance, as evidenced by increased conduction current, reduced breakdown strength, and compromised microstructural integrity. These findings suggest that, to improve the quality and reliability of XLPE cable production, engineering designs should prioritize controlling the pre-crosslinking process to ensure stable dielectric performance. Full article

The evaluation of the seismic behavior of masonry aggregates, which characterize Italian historic centres, is a challenging and widely debated topic in the field of structural engineering. These constructions, composed of several adjacent structural units, tend to exhibit both global and local damage when subjected to horizontal seismic actions—loads that were not considered at the time of their original construction. Developed over centuries of unplanned urban growth, they are based on empirical construction rules and locally sourced materials. Due to their poor thermal properties, these buildings are also affected by significant heat losses, resulting in reduced indoor comfort. In this context, the present study aims to evaluate the seismic performance of a masonry aggregate and two of its constituent structural units located in Visso, in the province of Macerata, an area severely affected by the 2016 Central Italy seismic sequence, both before and after the application of an innovative integrated retrofitting solution. The proposed strengthening system combines aluminium alloy exoskeleton with insulating sandwich panels, simultaneously addressing seismic vulnerability and energy inefficiency. The assessment is carried out through numerical analyses, including nonlinear static and dynamic approaches, to achieve a comprehensive understanding of the structural response. Moreover, a comparative analysis between the masonry aggregate and the two individual structural units, modelled as isolated buildings, is performed to investigate the influence of structural interaction among adjacent units. The results demonstrate the effectiveness of the proposed retrofitting strategy, highlighting a significant improvement in global stability. Furthermore, the comparison confirms the critical role of inter-unit interaction and underscores the necessity of modelling historic masonry aggregates rather than isolated buildings to obtain a more realistic seismic performance evaluation. Full article

Thermal stress is an important factor affecting the long-term performance of solid insulation in GIS/GIL, and the physicochemical properties of insulating materials play a crucial role in governing surface charge dynamics. This study investigates the influence of accelerated thermal aging on the surface charge behavior of Al₂O₃-doped epoxy resin insulators. Different aging severities were applied to simulate long-term service conditions, and charge accumulation and dissipation characteristics were correlated with physicochemical evolution revealed by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). The results indicate that increasing aging severity reduces the charge accumulation rate while increasing the saturated surface charge density. Voltage polarity significantly influences surface charge behavior: a relatively uniform distribution is observed under positive polarity, whereas localized charge clusters are more likely to form under negative polarity. Thermal aging also accelerates the development of surface defects and increases polar functional groups, resulting in degraded insulating performance. These findings clarify the relationship between thermal aging, physicochemical evolution, and surface charge dynamics in epoxy-based insulation systems. Full article