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This study analyzes the impact of anomalous diffusive heat equations (GCE) on the photoacoustic (PA) signal of the optically opaque two-layer sample measured in the gas-microphone configuration with minimum volume cell. We calculated the temperature distribution in the sample based on classical, hyperbolic, and two generalized fractional theories of heat propagation, including anomalous diffusion effects. Using the composite piston model, we derived the models of both the thermoelastic (TE) and thermodiffusion (TD) components as well as the total PA signal. In the analyses, we used opaque aluminum samples with an opaque dye coating. The results indicate that even small changes in fractional order of coating significantly affect the PA response of analyzed structure.

In recent years, ancient wooden building fires have been a hot issue that has not been properly solved. The existing ancient wood buildings objectively have serious natural ageing phenomenon, among which the dry and wet alternating ageing phenomenon of wood caused by water is the most serious. However, the phenomenon of dry and wet alternating ageing pays less attention to the influence of wood combustion. Therefore, this study took the typical wood species of ancient wooden buildings as the research object, based upon the natural ageing phenomenon of these buildings, determining the artificial acceleration of dry and wet alternate ageing method, to obtain dry and wet alternate ageing wood. The thermal diffusion coefficient of dry and wet ageing wood was analysed by thermal property experiments. Using differential scanning calorimetry experiment, we appraised the change law of heat flow in the combustion process of dry and wet ageing wood, determined the characteristic peak intensity and stage continuous temperature of dry and wet ageing wood, and mastered the change characteristics of wood in different thermal release stages affected by dry and wet alternating ageing. Finally, the apparent activation energy distribution of ageing wood in different exothermic stages was calculated and analysed by isoconversion method. The influence mechanism of alternating dry and wet ageing on wood combustion thermal release behaviour was revealed. The results show that the main thermal release of dry–wet ageing is the stage of volatiles precipitation. The alternate ageing of dry and wet has the greatest impact on the energy demand of thermal response in the accelerated thermal release stage. The influence of alternating dry and wet ageing on different types of wood in the rapid exothermic stage is quite different.

The thermal motion of stiff filaments in a crowded environment is highly constrained and anisotropic; it underlies the behavior of such disparate systems as polymer materials, nanocomposites, and the cell cytoskeleton. Despite decades of theoretical study, the fundamental dynamics of such systems remains a mystery. Using near-infrared video microscopy, we studied the thermal diffusion of individual single-walled carbon nanotubes (SWNTs) confined in porous agarose networks. We found that even a small bending flexibility of SWNTs strongly enhances their motion: The rotational diffusion constant is proportional to the filament-bending compliance and is independent of the network pore size. The interplay between crowding and thermal bending implies that the notion of a filament's stiffness depends on its confinement. Moreover, the mobility of SWNTs and other inclusions can be controlled by tailoring their stiffness.

Lock-in thermography is a widely adopted infrared nondestructive testing technique that detects subsurface defects by applying modulated thermal waves and analyzing the resulting surface temperature variations. However, quantitatively characterizing subsurface defects at varying depths remains a significant challenge. This study explores the lateral resolution of subsurface defect detection using phase-based lock-in thermography, integrating analytical modeling, finite element simulation, and phase difference analysis. The results demonstrate that defect visibility and boundary definition are highly influenced by the excitation frequency. The thermal diffusion length, which is inversely proportional to the square root of the excitation frequency, governs both the penetration depth and the lateral spread of thermal energy. Higher frequencies enhance lateral resolution, whereas lower frequencies improve the detectability of deeper defects. Detection becomes particularly difficult for defects with small radii or low radius-to-depth ratios. A critical radius-to-depth threshold of 2 is identified as essential for reliable boundary delineation. These findings offer practical guidance for selecting excitation frequencies to achieve an optimal balance between depth sensitivity and lateral resolution in thermal-wave-based nondestructive evaluation.

The effect of T4 and T6 treatment on the microstructures, precipitates, thermal expansion and thermal conductivity properties of Mg-2Nd-4Zn alloys was systemically investigated. The number of NdZn 2 phase increased subjected to T6 treatment. The coherent relationship between the NdZn 2 phase and Mg matrix was observed in the Mg-2Nd-4Zn alloys, which plays a great influence on improving the thermal expansion, thermal conductivity and mechanical properties of Mg-2Nd-4Zn alloys. The decrease in the coefficient of thermal expansion (CTE) and the thermal conductivity of Mg alloys were ascribed to the existence of solute atoms in alloys after the T4 treatment. It was also found that the T6-treated alloy has smaller area of the hysteresis loop, which has better thermal stability. Therefore, the high performance was mainly due to T6 treatment, the thermal conductivity of T6-treated Mg-2Nd-4Zn alloy is 124.4 K·m −1 ·K −1 at room temperature, and TYS of 235.5 MPa, CYS of 393.7 MPa, elongation of tension and compression are 31 and 27%, respectively.

The current study aims to investigate the thermal-diffusion and diffusion-thermo effects on heat and mass transfer in third-grade fluid with Darcy–Forchheimer relation impact over an exponentially inclined stretching sheet embedded in a porous medium. The proposed mechanism in terms non-linear and coupled partial differential equations is reduced to set of ordinary differential equations by employing an appropriate similarity variable formulation. The reduced form of equations is solved by using the MATLAB built-in numerical solver bvp4c. The numerical results for unknown physical properties such as velocity profile, temperature field, and mass concentration along with their gradients such as the skin friction, the rate of heat transfer, and the rate of mass transfer at angle of inclination α=π/6 are obtained under the impact of material parameters that appear in the flow model. The solutions are displayed in forms of graphs as well as tables and are discussed with physical reasoning. From the demonstration of the graphical results, it is inferred that thermal-diffusion parameter Sr velocity, temperature, and concentration profiles are augmented. For the increasing magnitude of the diffusion-thermo parameter Df the fluid velocity and fluid temperature rise but the opposite trend in mass concentration is noted. The current results are compared with the available results in the existing literature, and there is good agreement between them that shows the validation of the present study.

In high-humidity environments, the epoxy resin solid insulation materials of high-frequency transformers are prone to aging, resulting in varying degrees of deterioration in the material’s dielectric properties and other aspects. To enhance the adaptability of epoxy resin in high humidity environments, this paper, based on the molecular dynamics simulation method, establishes epoxy resin-based nanocomposites with doped nanofillers: a pure epoxy resin model and three epoxy resin models, respectively, doped with carbon nanotubes, graphene(GR), and SiO2. Based on the above models, using LAMMPS-17Apr2024, the thermal diffusion coefficients (thermal conductivity and specific heat capacity), glass transition temperatures, and dielectric constants under different moisture contents are calculated. The results show that the various properties of the epoxy resin nanocomposites doped with nanofillers have been improved to varying degrees. Among them, the GR/epoxy resin composite model shows the most significant improvements in thermal conductivity, thermal diffusivity, and glass transition temperature, and the SiO2/epoxy resin composite model has the best dielectric properties. Considering the high-temperature operation conditions and heat dissipation requirements of the high-frequency transformer, the GR-enhanced epoxy resin becomes the optimal filler choice.

The current investigations are carried out to study the influence of the Darcy–Forchheimer relation on third-grade fluid flow and heat transfer over an angled exponentially stretching sheet embedded in a porous medium. In the current study, the applied magnetic field, Joule heating, thermaldiffusion, viscous dissipation, and diffusion-thermo effects are incorporated. The proposed model in terms of partial differential equations is transformed into ordinary differential equations using suitable similarity transformation. The reduced model is then solved numerically with the help of MATLAB built-in function bvp4c.The numerical solutions for velocity profile, temperature profile, and mass concentration under the effects of pertinent parameters involved in the model are determined and portrayed in graphical form. The graphical effects of the skin friction coefficient, the Nusselt number, and the Sherwood number are also shown. From the displayed results, we conclude that when the Joule heating parameter is enlarged, the velocity and the temperature of the fluid are increased. We observed that while enhancing the viscous dissipation parameter (Eckert number) the fluid’s velocity and temperature increase but decreases the mass concentration. By increasing the values of the thermal-diffusion parameter, the velocity distribution, the temperature field, and the mass concentration increase. When the diffusion–thermo parameter rises, the velocity field and the temperature distribution increase, and the reverse scenario is seen in the mass concentration. The results of the current study are compared with already published results, and a good agreement is noted to validate the current study.

This study presents the design and fabrication of a glass fiber–poplar veneer composite plate, investigating how varying interlayer configurations of glass fiber (single- and double-layer) and the arrangement of poplar veneer layers (odd and even) impact the mechanical and thermal insulation characteristics of these composite plates. Compared to plywood made from natural wood, glass fiber significantly improved the properties of fast-growing poplar plywood. The highest impact strength increased by 3.62 times, while the flexural strength increased by 26.22% and the tensile strength by 29.66%. The thermal diffusion coefficient of the experimental group decreased by 40.74%, indicating better insulation. Interestingly, single-layer glass fiber is superior to a double-layer structure in terms of thermal insulation. An optimal interlayer structure was identified, comprising one veneer layer between two layers of glass fiber cloth, repeated three times. Abaqus 2019 was used for finite element analysis (FEA). The simulation results agree with the experimental data to within 5%. These findings confirm the importance of structural configuration in determining the properties of composite materials, providing a theoretical basis for the structural design of fiber–reinforced composite materials.

The article presents the results of research on the application of innovative thermal diffusion zinc coating technology with the recirculation of the reactive atmosphere to high-strength grade 10.9 bolts. The innovation of this method consists in the introduction of reactive atmosphere recirculation and the application of coating powder mix which contains zinc powder and activator. Recirculation of the reactive atmosphere ensures its uniform composition, while the presence of an activator intensifies the process of saturating steel surface with zinc, which boosts the efficiency of active agents. Coatings were created at 440 °C and a heat soaking time of 30–240 min. Coating structure (SEM) was exposed, chemical composition in microsites (EDS) was defined, and coating phase structure (XRD) was identified. The kinetics of coating growth were defined. It was found that the increment of coating thickness was controlled by square root of soaking time. Coatings obtained using innovative thermal diffusion zinc coating technology had a two-layer structure. At the substrate, a compact layer of phase Γ1 (Fe11Zn40) was created, which was covered with a layer of phase δ1 (FeZn10). The new method of thermal diffusion zinc coating will alow for the creation of coatings of very good corrosion resistance while maintaining strength properties of bolts defined as strength class 10.9.