Thermal Diffusion Coefficient Research Articles

Heat transfer in two-zone thick-walled pipes with axial varying periodic temperature boundary condition

The combined heat transfer in thick-walled pipes is investigated by also considering axial heat conduction. The problem considers a two-zone infinite pipe. There is a constant outer wall temperature boundary condition in the upstream region of the pipe. In the downstream region, the outer wall temperature is assumed to vary periodically in the axial direction spatially. This problem, where the flow is assumed to be laminar, is solved numerically by the finite difference method. The effects of the basic parameters of wall thickness ratio, Peclet number, wall-fluid thermal conductivity coefficient ratio and wall-fluid thermal diffusivity coefficient ratio on the interface heat flux are investigated. The effects of the axial dimensionless frequency on the results are also taken into account in the studies. The results obtained are highly dependent on the parametric values. It is observed that the wall thickness ratio is more effective than the other parametric values. In addition, it can be said that the pipe wall and fluid axial conduction cause heat transfer to the upper flow region at a non-negligible scale.

ЗАКОНОМЕРНОСТИ ИЗМЕНЕНИЯ ТЕПЛОФИЗИЧЕСКИХ ПОКАЗАТЕЛЕЙ ЭЛАСТОМЕРОВ НА ОСНОВЕ ЭТИЛЕНПРОПИЛЕНОВОГО КАУЧУКА, СОДЕРЖАЩИХ МИКРОСФЕРЫ

The influence of hollow glass microspheres on the thermal properties of fire-protective materials based on ethylene-propylene rubber was assessed. The linear dependence of thermal diffusivity and thermal conductivity coefficients of compositions on the content of glass microspheres has been established. An assumption was made about the occurrence of non-covalent (supramolecular) interactions of elastomer compositions on the surface of the microspheres.

Kinetics of thermal and photoinduced diffusion of Ag into thin layers of chalcogenide glasses

This study examines the kinetics of thermal diffusion of silver in Ag-GeSe2 and Ag- As10Ge30S60 thin film structures during prolonged storage in the dark at room temperature, as well as the effects of plasmon-enhanced photostimulated diffusion of silver into As10Ge30S60 films. Ag diffraction gratings with a period of 519 nm were used to excite surface plasmon-polaritons (SPP) at the silver-chalcogenide glass interface. It was found that the thermal diffusion coefficient of silver into GeSe2 is significantly higher than into As10Ge30S60. For Ag– As10Ge30S60, photostimulated silver diffusion coefficients were measured with and without SPP excitation. SPP excitation triples the photostimulated Ag flux into As10Ge30S60. Although photosensitivity decreases over time, the plasmon-stimulated increase in Ag flux remains stable. Additionally, As10Ge30S60 thermally doped with silver shows much higher optical absorption at the probing wavelength compared to the photodoped layer with the same silver concentration. Possible mechanisms of these layers formation are discussed.

DFT investigations of doping effects on the structural stability, thermal diffusion, and absorption/desorption kinetics in cubic, hexagonal, and monoclinic Mg2NiHx hydrides

The pseudo-potential plane-wave method, based on Density Functional Theory (DFT) and using the Generalized Gradient Approximation (GGA), is applied to investigate the effects of progressive hydrogen insertion on the structural stability and energetics of Mg2NiHx hydrides. The obtained results indicate that Mg2Ni crystallizes in the hexagonal (P6222) structure. Taking into account the site preference of H atoms, the progressive hydrogenation of Mg2Ni favors the formation of Mg2NiHx hydrides in cubic (Fm-3m) and monoclinic (C2/c) phases rather than the parent hexagonal phase. The alloying effects of Cu, Y, Si, Ti, Cr, and Fe on the structural stability and absorption/desorption kinetics of monoclinic Mg2NiH4 are also investigated. More particularly, systems with Cu and Si additions have the lowest desorption temperatures, as confirmed by Molecular Dynamic (MD) calculations. The thermal diffusion is well observed in all studied compounds. The corresponding average thermal diffusion coefficients are mainly attributed to hydrogen atoms and are increased by the addition of Cu. These trends are expected to have an important role in phase transitions observed during hydrogen insertion. The present study based on DFT and MD calculations shows that doped Mg2NiHx are promising hydrides with interesting kinetic behavior. The obtained results can be useful for future experimental studies devoted to improving hydrogen absorption/desorption temperatures, low energy costs, and high atomic hydrogen storage capacities in Mg2Ni.

Analytical solutions for large-deflection bending of variable-thickness inhomogeneous functional graded composite circular plates with parameterized boundaries under hygro-thermo-mechanical loads

A brand-new hygro-thermo-mechanical bending model of the inhomogeneous concave and convex composite circular plates having varying thickness undergoing large deformation resting on nonlinear tri-parameter spring and shear elastic layers is proposed. Three-dimensional analytical hygrothermal field of circular plate is demonstrated with non-uniform thermal and moisture diffusion coefficients in axial variation, while thickness and elastic module of material are modeled in quadratically change and sufficiently summarized in normalization. The circled boundaries with arbitrary translational and rotational constraints are parameterized with feasible region of elastic parameters highlighted in rectangular domain by Linear Programming method. Two reduced-order integro-differential governing equations for the composite circular plates under extreme load have been derived, while analytical bending solutions are obtained by an employed homotopy-based analytical scheme with accuracy verified and convergence accelerated by truncation and iteration. Whether thickness or elastic module of composite material is variable, the final outcome on plate structural strength is the discrepancy of bending stiffness with different load capacity, with the former revealing more sensitive than the latter under the condition of same values. Once amplitude and distribution of hygrothermal load are determined, influence on large-deflection bending of circular plates exists at a limited range of nonlinearity, while non-uniform distribution of thermal expansion and moisture concentration aggravates bending effects only within this range.

New in assessing the fire resistance of reconstructed reinforced concrete ribbed building panel

The article describes the innovative application of a methodology for assessing the design fire resistance of a reconstructed reinforced concrete ribbed floor panel based on the criterion of the occurrence of a limit state based on loss of load-bearing capacity. In this case, the fire resistance limit of a bending element is established without thermal force destruction based on a set of single quality indicators of structural concrete and reinforcing steel, which simplifies engineering calculations and reduces the cost of expensive experiments. The results of a study of the influence of the geometric dimensions of a reconstructed reinforced concrete ribbed panel, the heating scheme of the design section in fire conditions, the placement of the main and additional reinforcement in the design section, the depth of the cores of the main and additional reinforcement and the degree of its fire protection, the thermal diffusion coefficient of structural concrete, the magnitude of the test load on the panel are presented. and the intensity of stress in the rods of longitudinal working reinforcement to the design fire resistance indicator, which is established based on the loss of load-bearing capacity. The use of the new proposed technical solution makes it possible to determine the design fire resistance of a reconstructed reinforced concrete ribbed panel without natural thermal force effects, simplifies engineering calculations, increases the reliability of statistical quality control of reinforced concrete materials and non-destructive tests, and reduces experimental costs.

Thermophysical properties of AlxCoCrCuFeNi high entropy alloys

The AlxCoCrCuFeNi (x = 0.25, 0.5, 1, 2) high entropy alloys (HEAs) were prepared by arc melting and spray casting techniques. Their microstructures, hardness, and thermophysical properties such as fusion enthalpy, entropy, thermal diffusion coefficients, thermal expansion coefficients, were investigated. XRD results indicated that AlxCoCrCuFeNi (x = 0.25 and 0.5) alloys were composed of a high-entropy FCC phase and Cu-rich nanophase. As the Al content increased to 1 and 2, the phase structures included the AlNi-rich B2 phase, FeCr-rich A2 phase and Cu-rich nanophase. With the increased Al content, the microstructures of AlxCoCrCuFeNi HEAs transitioned from coarse dendrites to petal-like dendrites, and the grains were continuously refined. Moreover, the Al additions reduced the density whereas increased the Vickers hardness of the alloys. The maximum hardness observed in Al2CoCrCuFeNi HEA was approximately 2.4 times greater than that of the Al0.25CoCrCuFeNi HEA. The thermal diffusion coefficients of alloys initially increased and subsequently decreased as the temperature elevated. The phase transformation induced by Al content was an effective method for rapidly homogenizing the internal temperature of alloys. Furthermore, the crystal structure, elemental segregation, lattice distortion, enthalpy and entropy of fusion, and lattice vibration frequency all mutually affected the thermal diffusion and expansion coefficients of AlxCoCrCuFeNi HEAs.

Heat diffusion coefficient study of polymers based on interpretable machine learning

Abstract. Polymers hold significant application value across various fields of modern society, with different application scenarios requiring specific thermal diffusivity coefficients. Finding polymer materials with targeted thermal diffusivities is crucial. However, due to the vast variety and complex structures of polymers, constructing a unified structured dataset for machine learning modeling is challenging. Although machine learning has shown great potential in materials science, it has rarely been applied to predict the heat diffusion coefficient of polymers. This paper constructs a dataset for predicting the thermal diffusion coefficient of polymers using a publicly available dataset by transforming the SMILES code of polymers into eight features with practical physical and chemical meanings. Using the Random Forest algorithm, training with 400 of these data and randomly selecting 200 of them for cross-validation, the accuracy of the test set reached 0.9. Additionally, through interpretability analysis, we found that the molecular weight of the polymer monomers, the TPSA (the polar surface area of the molecule), and the NRB (the number of rotatable bonds) are the main features affecting the polymer thermal diffusion coefficient. An increase in the TPSA and the NRB positively contributes to the thermal diffusivity, while an increase in molecular weight negatively contributes. Our study provides a new method for the prediction of polymer thermal diffusivity and creates a new paradigm for the study of polymer thermal diffusivity, promoting further development in this field.

Effect of Laser on the Interface and Thermal Conductivity of Metallized Diamond/Cu Composite Coatings Deposited by Supersonic Laser Deposition.

To achieve the rapid heat dissipation of components in the industrial field, the heat dissipation coating is prepared on the surface, which is conducive to improving the service life of the parts and greatly reducing the industrial costs. In this paper, metallized diamond/Cu composite coatings were fabricated on 1060Al substrate by supersonic laser deposition. The composite coatings were prepared at a nitrogen pressure of 3.0 MPa, a scanning speed of 10 mm/s, and a 1060 nm semiconductor coupled fiber laser with different laser power. The research results show that the laser power affects the interface bonding by affecting the temperature of adiabatic shear instability during particle impact. The metallized diamond forms a good bonding at the interface through the plastic deformation of the Cu matrix. Appropriate parameters ensure that the jet does not affect the subsequent particle deposition and build a good heat transfer bridge to elevate the heat transfer efficiency. The coating prepared at a laser power of 1000 W has the highest thermal diffusion coefficient of 89.3 mm2/s and thermal conductivity of 313.72 W/(m·K), which is 8.92% higher compared to the coating prepared without laser. Experiments with thermal imaging have also demonstrated that the coating at optimal parameter transferred heat faster. Our research provides a technical guidance for rapid preparation of high-quality heat dissipation coatings in industry.

Atomic cluster expansion interatomic potential for defects and thermodynamics of Cu–W system

The unique properties exhibited in immiscible metals, such as excellent strength, hardness, and radiation-damage tolerance, have stimulated the interest of many researchers. As a typical immiscible metal system, the Cu–W nano-multilayers combine the plasticity of copper and the strength of tungsten, making it a suitable candidate for applications in aerospace, nuclear fusion engineering, and electronic packaging, etc. To understand the atomistic origin of the defects (e.g., vacancies, free surfaces, grain boundaries, and stacking faults and thermodynamical properties), we developed an accurate machine learning interatomic potential for Cu–W based on the atomic cluster expansion (ACE) method. The Cu–W ACE potential can faithfully reproduce the fundamental properties of Cu and W predicted by density functional theory (DFT) calculations. Moreover, the thermodynamical properties, such as the melting point, coefficient of thermal expansion, diffusion coefficient, and equation of the state curve of the Cu–W solid solution, are calculated and compared against DFT and experiments. Monte Carlo molecular dynamics simulations performed with the Cu–W ACE potential predict the experimentally observed phase separation and uphill diffusion phenomena. Our findings not only provide an accurate ACE potential for describing the Cu–W immiscible system but also shed light on understanding the atomistic mechanism during the Cu–W nano-multilayers formation process.

Current, core channel radius, and related parameters of channel plasma in artificially triggered lightning

Based on plasma physics methods, the relationship among the channel current (i), core channel radius (rcc), and other related parameters including electrical conductivity (σ), thermal conductivity (λe), and thermal diffusion coefficient (DeT) was investigated and strong interdependence was found among these parameters. Then, these dependent relationships together with the measured electron temperature (Te) and electron density (ne), derived from spectral diagnostics, were applied to determine the measured results on the i, rcc, σ, λe, and DeT of channel plasma in artificially triggered lightning along with their measured accuracies. Good accordance can be found with the aid of comparisons with other measurements of the artificially triggered lightning [L. Cai et al., J. Electrost. 109, 103537 (2021)].

Dynamic behaviors of interfacial oxides and elements during the ultrasonic-assisted diffusion bonding of 6063Al alloys

Efficiently breaking the oxide layer and rapidly diffusing of elements at low-temperature has been a longstanding goal in the diffusion bonding (DB) of Al alloys. To break the interfacial oxide layers and accelerate atomic diffusion, ultrasound energy was introduced during the DB of 6063Al. A full Zn–Al eutectoid joint was manufactured via a pure Zn interlayer at 360 °C in atmospheric by an ultrasonic-assisted diffusion bonding (U-DB) at only an ultrasonic vibration of10 min. During U-DB, brittle cracks were formed in the interfacial oxide layers due to high strain rate induced by ultrasonic action. Zn diffused into Al alloy through the brittle cracks in oxide layers via “subcutaneous diffusion,” forming a Zn–Al eutectoid diffusion region between the Al alloy and oxide layer. The oxide fragments irregularly migrated to the center of the joint due to Kirkendall effect and ultrasonic action, finally dispersed in the bonded metal. The bonded metal finally transformed as a full Zn–Al eutectoid phase after consuming interlayer. The shear strength of the Zn–Al eutectoid joint reached 82.6 MPa. The Zn–Al mutual diffusion coefficient of U-DB at 360 °C was ∼0.6 μm2/s, which was about 20 times higher than the thermal diffusion coefficient under same temperature condition. Additionally, the mechanism of ultrasonic-assisted diffusion based on the strain-driven diffusion mode was discussed in detail.

Measurement of thermophysical parameters of artificial skin

Computer methods for process research and methods for processing the measurement results of the parameters of these processes are widely used in biology and medicine. Therefore, the problem of automation of biophysical measurements and computer processing of the results of such experiments is relevant. In the treatment of wounds and burns with a large surface area of tissue damage, medicine has to resort to artificial skin. A procedure for studying thermal processes in artificial skin and measuring its thermophysical parameters was developed. The measurement process was described. The thermophysical parameters of the artificial skin samples used in medicine for the treatment of wounds and burns were determined. The samples of the artificial skin used were made in Ukraine. Each sample was made from six layers of skin. To control the temperature distribution in the sample between the skin adjacent layers and on the surface of the sample, thermocouples were placed. The surface of the sample was heated with an incandescent lamp. The thermocouple signals were sent to an analog-to-digital converter (ADC), amplified, and digitally transmitted to a computer. Processing was carried out using the ADC software and the MATHCAD program. A mathematical model was obtained. For this purpose, a differential equation describing thermal processes in the sample was solved. The found temperature distribution function and its changes over time are in a good agreement with experimental data. The analysis of the function allows finding the thermal conductivity coefficient of artificial skin, its volume heat capacity, thermal diffusivity coefficient, and heat exchange coefficient with the external environment. The proposed method of measuring and processing experimental data makes it possible to detect main thermophysical parameters of artificial skin. Based on these results, a theoretical model was obtained that well describes the course of thermal processes in artificial skin, which makes it possible to predict the course of these processes. Such method is based on heating the skin with optical radiation. The thermal conductivity and thermal diffusivity of artificial skin are significantly less than such parameters of human skin, which should be considered when using it.

Hygroscopic hydrogel-based cooling system for photovoltaic panels: An experimental and numerical study

Thermal management is an essential aspect of photovoltaic (PV) system design because of the negative effects of high temperatures on the efficiency of PV panels. The use of hygroscopic hydrogels for the evaporative cooling of PV panels is an emerging technique that has attracted attention owing to the high latent heat and recyclability of these materials. However, a comprehensive understanding of the heat and mass transport mechanisms in hygroscopic hydrogels is necessary. Factors that would ensure the long-term performance of PV panel/hydrogel (PV/HG) systems under real-world conditions are still poorly understood, and the intrinsic properties of hydrogels and the effect thereof on their cooling performance have hitherto remained unexplored. Herein, we propose a mathematical model for hydrogel-cooled PV panels to study the heat and mass transfer mechanisms of PV/HG systems in practical environments. The model is used to examine the impact of the thermal conductivity, diffusion coefficient, and thickness of the hydrogel on the performance of the PV/HG system. Unlike previously reported approaches to enhance the efficiency, in this study, the external heat transfer resistance and internal mass transfer resistance were identified as the primary controlling factors. Enhancement of the thermal conductivity of the hydrogel is shown to have a limited effect on the performance, whereas improving the water diffusion within the hydrogel significantly boosts the system efficiency. Optimally, the thickness of the hydrogel must be such that it balances the heat and mass transfer distances with the available water volume. During the summer in Guangzhou, China, a 6-mm thick layer of hydrogel lowered the temperature of a PV cell by up to 7.5 °C to increase the daily power generation by 2.1%. Analysis of the nationwide situation showed that hydrogels have substantial potential for lowering the peak PV panel temperatures (by as much as 19.3 °C) to mitigate fluctuations in the output power. Our findings offer valuable insights into the design of PV/HG systems towards improving their performance.

Enhanced comprehensive properties of alumina ceramic shells by a pennisetum fiber/AlF3•3H2O powder hybrid system

The strength and permeability to gas of ceramic shells are key factors affecting the quality of castings. This research aims to improve the properties of alumina-based ceramic shells (i.e., Al2O3 and SiO2) using a combination of pennisetum fiber and AlF3•3H2O powder. The pennisetum fiber can improve the green strength of ceramic shells, while AlF3•3H2O powder can improve the high-temperature strength of ceramic shells by inducing the generation of mullite (3Al2O3•2SiO2) whiskers at high temperatures. Meanwhile, the mixture of pennisetum fibers and mullite whiskers can also improve the permeability to gas of the ceramic shell. As a result, the modified ceramic shell shows a clear increase in the above-mentioned properties, including 43 % of the green strength, 100 % of the permeability to gas, and 30 % of the thermal diffusion coefficient. In addition, the high-temperature bending strength and deformation under the weight of the ceramic shells are also obtained.

Regulating the thermophysical properties of rare earth cerates through high entropy design and substitute

Cerate ceramics are considered promising candidates for the new generation of thermal barrier coatings. However, in the middle temperature area (473–673 K), the CTE mismatch due to the thermal contraction often results in coating failure. The aim of this work is to develop an innovative component regulation method that significantly reduces the thermal conductivity and alleviates the thermal contraction. Cerates exhibit a low thermal diffusion coefficient, primarily attributed to the impact of extrinsic phonon scattering mechanisms. Our comprehensive analysis encompassed various factors such as point defects, the degree of size and mass disorder, grain interfaces, and lattice distortion. By employing high entropy design and doping strategies, we have successfully alleviated the thermal contraction phenomenon in cerates, while maintaining their high CTE. Furthermore, an in-depth investigation of the valence states of elements and lattice energy was conducted to elucidate the thermal contraction mechanism of cerates in the middle temperature area.

Study of the thermal diffusivity in low-response optical systems combining a thermal lensing approach with a standard addition method

Abstract Thermal lensing is a local effect produced by the incidence of a light beam that heats a part of an absorbent material. Mathematical modeling of this photothermal phenomenon allows the determination of the medium’s thermal diffusivity. A pumping-modulated laser (405nm) induces the thermal lensing effect, and a test laser (650nm) generates the photothermal signal measured as a function of the modulation. The thermal diffusivity is obtained from a curve fit of the signal (calibrated for ethanol). In this work, the thermal diffusion coefficients of low-absorbance nanoparticle suspensions are established. This was achieved through the application of a standard addition method. The added analyte, enhance the optical response of SiO 2 nanoparticle suspensions. Different aliquots of tartrazine (analyte) resulted in different values for the thermal diffusion of the samples. It was found that the experimental coefficients of this colloids agree with the theoretical model. Finally, a linear regression allowed to find the thermal coefficient in the zero concentration point.

Durability and thermal insulation properties of glazed hollow bead concrete with nanoparticles in marine atmospheric environment

Industrial and civil buildings in coastal areas have been in the marine atmosphere for a long time and are especially susceptible to the combined effects of carbonation and salt spray, which accelerate the deterioration of concrete durability and the reduction of thermal insulation performance. This paper focused on the effect of nano-SiO2 and nano-Al2O3 on the durability and thermal insulation of glazed hollow bead concrete (GC) under a salt spray carbonation environment, and analyzed the mechanism of nanoparticles on the improvement of durability and thermal insulation of GC by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) microscopic tests. The results showed that both nano-SiO2 and nano-Al2O3 incorporation could improve the durability and thermal insulation of GC to a certain extent. The optimal amount of both nanoparticles was 2 %, and nano-SiO2 had a stronger beneficial effect than nano-Al2O3. In comparison to GC, the free Cl− content in the surface layer of GCNS20 and GCNA20 after 56 cycles was decreased by 33.33 % and 27.22 %, respectively. Furthermore, the carbonation depths of GCNS20 and GCNA20 were decreased by 42.83 % and 36.38 %, respectively. The thermal conductivity of GCNS20 and GCNA20 decreased by 24.86 % and 17.34 %, respectively, while the thermal diffusion coefficients were reduced by 33.22 % and 23.73 %, respectively. The incorporation of nanoparticles effectively reduced the microcracks and pores in GC, improved its internal structure, and reduced the possibility of thermal bridge formation. In addition, the incorporation of nanoparticles significantly reduced the production of erosion products such as CaCO3 and Friedel's salt in GC.

Effect of phase change materials on thermophysical properties of asphalt mixtures and snow melting performance

The increased Thermal Conductivity and Thermal Diffusion Coefficient of asphalt mixtures means that the material is able to conduct and disperse heat more efficiently. In winter, this property can be used to accelerate the melting process of snow and ice, reducing the risk of road sliding due to snow and ice build-up. In this study, the thermal conductivity, thermal diffusion coefficient, and specific heat capacity of phase change asphalt (PCA) mixtures were investigated using a transient flat-plate heat source method. Analysis was performed with a thermal constant analyzer, a custom-designed thermal conductivity experiment, and a differential scanning calorimeter. Additionally, a phase change asphalt mixture thermoregulation rutting plate was prepared to evaluate its thermoregulation and snow and ice resistance under actual winter and indoor conditions. Results indicated that the thermal conductivity and thermal diffusion coefficient of PCA mixtures were superior to those of conventional asphalt mixtures. Notably, the specific heat capacity of these mixtures increased significantly within the phase change temperature range. The integration of phase change materials enhanced heat transfer within the asphalt mixtures, allowing for a delayed cooling process when temperatures decreased, with the maximum cooling range observed to be 2.8°C. Snow melting tests confirmed the early snowfall efficacy of the phase change asphalt mixture rutting plate, effectively achieving minimal snow accumulation and demonstrating the capability of 'melting light snow.'

Microstructural, thermal characterization and CMAS corrosion resistance of novel quaternary (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 high entropy disilicate material

A novel (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 high entropy disilicate quaternary composition was synthesized from commercial oxide powders using ball milling and sintering processes as a candidate material for environmental barrier coatings (EBC). As-synthesized high entropy disilicate powders were sintered at different durations (12, 18, and 24 h) at 1600 °C in a muffle furnace before characterization. The XRD and SEM analyses revealed the single-phase monoclinic structure (β-type) with homogeneous elemental distribution for the sintered samples. The (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 samples exhibited low thermal diffusivity coefficient, low thermal conductivity, a close coefficient of thermal expansion (CTE) to SiC and a high temperature stability. The (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 samples were subjected to CMAS corrosion tests at 1300 °C with different durations (2, 12, and 24 h) to evaluate CMAS corrosion resistance. Additionally, Yb2Si2O7 samples were prepared and subjected to molten CMAS in the same way for comparison. Based on the results, the CMAS corrosion resistance was improved with (Y0,25Er0,25Tm0,25Yb0,25)2Si2O7 composition.