Dependence Of Thermal Diffusivity Research Articles

Quantitative characterization of archaeological bronzes based on thermal and compositional analysis

AbstractPulsed thermography has been applied to the quantitative characterization of the insertions of two ancient bronzes, the Boxer at Rest and the Hellenistic Prince. The analysis of the thermographic signal time dependence performed by a specifically developed model enabled the evaluation of the insertions’ thickness and of elements which could provide indications about the procedure followed for their insertion. This could be achieved by exploiting a semi‐empirical relation establishing the thermal diffusivity dependence on the total effective weighted concentration of Sn and Pb atoms obtained from the analysis of the values determined on samples containing different concentrations of Sn and Pb.

Infrared thermography for the thermal diffusivity evaluation in Sn-Pb bronze alloys: A tool for the investigation of ancient statuary

In this work, we report on the application of Pulsed Infrared Thermography for the analysis of the thermal diffusivity dependence on the composition of copper alloys with tin (Sn) and lead (Pb) concentrations typical of ancient bronze artefacts. To this aim, specifically prepared bronzes samples have been investigated. Both the measured thermal diffusivity values and those retrieved from the literature showed a decreasing trend with increasing Sn and Pb concentration. In the overall data analysis, the concentration of Pb atoms was weighted by a coefficient to account for their lower efficiency in reducing the thermal transport properties of the alloy with respect to the Sn atoms. Electrical conductivity values measured on the same samples showed a dependence very similar to that obtained for the thermal conductivity, pointing out the mainly electronic nature of the thermal conductivity in such samples.

Laser ablated silicon nanoparticles with selected solvents: A comparison of thermal diffusivity under different concentrations

In the present work, the basic optical characterisation and thermal diffusivity studies of silicon nanofluid were carried out by mode-matched dual-beam thermal lens technique. The silicon nanoparticles were synthesised in ethanol, water, DMSO, and ethylene glycol by pulsed laser ablation process using Q-switched Nd: YAG nanosecond laser of wavelength of 1064 nm. The concentration dependence of thermal diffusivity was examined for the prepared silicon nanofluids. A decreasing trend for the thermal diffusivity was found with the increasing concentration of silicon in nanofluid in each solvent. These declining traits in heat diffusivity of silicon nanofluid can be explored for thermal trapping applications such as thermal insulators.

Thermal Diffusivity Dependence with Highly Concentrated Graphene Oxide/Water Nanofluids by Mode-Mismatched Dual-Beam Thermal Lens Technique

The thermal properties of graphene oxide (GO) nanoparticles’ colloidal suspensions prepared using the microwave-assisted hydrothermal method were determined. The mode-mismatched dual-beam thermal lens technique was employed to measure the thermal diffusivity of GO nanoparticles for different concentrations in the base fluid. By fitting the experimental data to the theoretical expression, the characteristic time constant was determined. The thermal diffusivity of the fluids seemed to be strongly dependent on the presence of the nanoparticles, increasing from 15.02 ± 0.16 × 10−4 cm2·s−1 to 27.59 ± 0.51 × 10−4 cm2·s−1 for concentrations ranging from 0.82 %V to 4.00 %V of GO/H2O. As nanofluids concentration increased, a higher value of thermal diffusivity was obtained. The optical properties, morphology and chemical structure and functional groups of the nanoparticles were characterized by UV–Vis spectroscopy, transmission electron microscopy (TEM) and Fourier Transform infrared spectroscopy (FTIR). Two main absorption peaks at 230 nm and at 303 nm in the UV–Vis spectra were observed. TEM images revealed a uniform size distribution and spherical in shape NPs with mean diameter of 7.4 nm. This novel type of nanofluids have potential applications for heat transfer fluids like solar collectors and heat exchange systems.

Non-Boussinesq Low-Prandtl-number Convection with a Temperature-dependent Thermal Diffusivity

Abstract In an attempt to understand the role of the strong radial dependence of thermal diffusivity on the properties of convection in Sun-like stars, we mimic that effect in non-Oberbeck–Boussinesq convection in a horizontally extended rectangular domain (aspect ratio 16) by allowing the thermal diffusivity κ to increase with the temperature (as in the case of stars). Direct numerical simulations (i.e., numerical solutions of the governing equations by resolving up to the smallest scales without requiring any modeling) show that, in comparison with Oberbeck–Boussinesq simulations (two of which we perform for comparison purposes), the symmetry of the temperature field about the mid-horizontal plane is broken, whereas the velocity and heat flux profiles remain essentially symmetric. Our choice of κ(T), which resembles the variation in stars, results in a temperature field that loses its fine structures toward the hotter part of the computational domain, but the characteristic large scale of the turbulent thermal “superstructures,” which are structures whose size is typically larger than the depth of the convection domain, continues to be largely independent of the depth.

Thermophysical properties of lowland Histosols of the Upper Volga woodland (on the example of the Yakhroma river valley)

Annotation. The dependence of thermal diffusivity on volumetric humidity for Histosols developed on wood peat, underlain by sediment peat and mineral peat, was studied using Histosols from the Yakhroma Valley (Moscow Region). The determination was carried out at the stages of dreinage and humidification by the laboratory method of Kondratiev. For the stage of draining, the dependence has a more pronounced dome-shaped form than for the stage of saturation. The highest values of thermal diffusivity were achieved with a volumetric soil water content of 50-55% for Histosols on wood peat and 40-45% for agromineral peat. The approximation of the data was carried out according to the equation of Chang and Horton. As a result of comparing the approximation parameters, it was revealed that they do not significantly differ from each other, which indicates the absence of hysteresis of the thermal diffusivity from humidity for the thermal diffusivity curve, the unambiguous values of which can be used to simulate the temperature regime.

Dependence of thermal diffusivity on nanoparticle shape deduced through thermal lens technique taking ZnO nanoparticles and nanorods as inclusions in homogeneous dye solution

We are presenting our results of comparison of thermal diffusion behavior of composite media of nanoparticles and nanorods of ZnO in a homogeneous solution of fluorescein dye, done using the dual beam, pump-probe thermal lens technique. It was observed that both nanorods and nanoparticles can be used to control the thermal diffusivity of the composite fluid by changing the relative volume fractions. It was also observed that there is an optimum value for this volume fraction in the two cases considered. We have also explained this behavior using theoretical approach taking into account the Unit cell model, Brownian motion and the near field effects. We expect that this work will enhance the understanding of the influence of particle size, shape and the thermal properties of this novel composite which can widely find application in thermoelectric coolers, high performance thermal transfer liquids and in random lasing.

Correction to: Determination of the Dependence of Thermal Diffusivity with Moringa Concentration by Thermal Lens as a Sensitive Experimental Technique

Correction to: Determination of the Dependence of Thermal Diffusivity with Moringa Concentration by Thermal Lens as a Sensitive Experimental Technique

Determination of the Dependence of Thermal Diffusivity with Moringa Concentration by Thermal Lens as a Sensitive Experimental Technique.

The use of photothermal techniques has become of special importance due to their versatile application in the thermal characterization of materials. Therefore, the thermal lens technique in the mismatched dual-beam mode is an alternative, sensitive and non-evasive tool that was used in this research to determine the thermal diffusivity of Moringa oleifera. The dual arrangement of the thermal lens technique is based on the use of an Ar+Xe excitation laser (422 nm) and a He–Ne laser (632 nm) test laser. Moringa solutions were prepared by green synthesis with different concentrations ranging from 1.56 mg·mL−1, 3.12 mg·mL−1, 6.25 mg·mL−1 to 12.50 mg·mL−1. Different optical techniques (UV–vis, FTIR, XPS and EDS) were used to characterize the Moringa leaf powders. Results showed that the increase of thermal diffusivity could be related to the presence of functional groups and metallic elements in Moringa elemental composition. In this work, it was found that the thermal diffusivity of Moringa increases with increasing concentration. This study will be useful for application in heat transport and drug release.

Тепловые, магнитные и магнитотранспортные свойства быстрозакаленнго ленточного образца Ni-=SUB=-50-=/SUB=-Mn-=SUB=-35-=/SUB=-Al-=SUB=-2-=/SUB=-Sn-=SUB=-13-=/SUB=-

The heat capacity, thermal diffusivity, thermal conductivity, magnetization, and electrical resistance in a tape sample of Ni50Mn35Al2Sn13 alloy were studied. The temperature dependence of thermal diffusion shows pronounced anomalies in the form of minima associated with magnetic and magnetostructural transformations. The behavior of thermal conductivity and thermal diffusion indicates that the mean free path of heat carriers is limited by the structural imperfections of the tape. The transition of the sample to the martensitic phase is accompanied by a sharp increase in the electrical resistance, suggesting an increase in the electron relaxation rate due to structural distortions inherent in martensite. The magnitude of the magnetoresistive effect ∆ρ/ρ_0 in the field of 1.8T near the martensitic transition is reached 40%. The temperature hysteresis was revealed in the dependence ρ(T) near TC, which indicates the structural heterogeneity of the austenitic phase.

Measuring Thermal Diffusivity of Dilute Nanofluids Using Interferometry-Based Inverse Heat Transfer Approach

Measurement of thermophysical properties of nanofluids is essential to understand the heat transfer performance of nanoparticles suspended in base fluids. In this direction, as a definite advancement over the conventional methods, laser interferometry has been employed to study the dependence of thermal diffusivity of dilute nanofluids on increasing volume concentration of nanoparticles using the principles of inverse heat transfer. Two types of nanofluids, namely, and with de-ionized water as the base fluid, have been considered for this analysis. The experimental configuration consists of a layer of working fluid (water or nanofluid) contained between two differentially heated horizontal walls of a rectangular cavity. Temperature potential is applied to the fluid layer by raising the temperature of the upper horizontal wall of the cavity with respective to the lower one. Transient evolution of the thermal diffusion field (from top plate to the lower horizontal wall) has been recorded in the form of interferograms at various time instants. As the forward model, the transient form of heat diffusion equation has been analytically solved for a guessed value of thermal diffusivity. Finally, the experimentally determined temperature field has been compared with the analytical solution, and following the principles of inverse heat transfer, the thermal diffusivity of the working fluid has been calculated. The methodology developed has first been benchmarked by determining the thermal diffusivity of the base fluid, that is, water, and thereafter it has been employed to determine the corresponding thermophysical properties of the dilute nanofluids. Results showed an increase in the thermal diffusivity of dilute nanofluids as a function of increasing volume concentration of the nanofluids.

Appropriate metallic coating for thermal diffusivity measurement of nonopaque materials with laser flash method and its effect

Laser flash method is used as a standard method for the thermal diffusivity measurements, which required the absorber of the laser pulse and the emitter of the infrared ray. However, due to the transmission, the nonopaque materials are difficult to be measured with the laser flash method directly. Quartz glass disks were evaluated with the laser flash method to ensure the appropriate measuring condition. To verify the appropriate metallic conditions, different thick platinum and gold coatings were sputtered on the both surfaces of the glass disks by controlling the sputtering time. Sample thickness dependence and temperature dependence of thermal diffusivity for quartz glass were also evaluated with the metallic coatings. In addition, thermal diffusivity of Al2O3-TiC ceramics disks, which is a certified reference material supplied by NMIJ, were also evaluated with and without the metallic coating to ensure the effect of metallic coating by the laser flash method. A 32.7 nm-thick gold coating was found to be the appropriate measurement condition in consideration of stability, operability and economic efficiency for the laser flash method.

Particle size and concentration effect on thermal diffusivity of water-based ZnO nanofluid using the dual-beam thermal lens technique

In the present work, we experimentally investigate the size and concentration dependence of the thermal diffusivity of water-based ZnO nanofluid. The results show an increase in thermal diffusivity both by increasing the particle size from 5.6 to 16.6 nm as well as nanoparticle concentration in the range 0.02–0.1 mg/ml. It was also observed that there is a 4% enhancement in thermal diffusivity of the nanofluid for an optimum value of nanoparticle size and concentration. The dependence of thermal diffusivity on the particle size and concentration can give a great insight into the inter-particle interaction and the aggregation dynamics in nanofluid.

Thermal diffusivity of Al-Si cast alloys for internal combustion engines

International regulations on the reduction of fuel consumption and CO2 emissions to the atmosphere have made the transportation industry in general, and the automotive in particular, to look for the improvement of aluminium alloys used in manufacture of internal combustion engines. Smaller and lighter engines able to develop higher power outputs rely on increasing the temperature within the combustion chamber, which imply augmenting thermal and mechanical demands of the alloy used in the manufacture of powertrain components. Al-Si alloys are used due to their combination of low density, high strength and the feasibility of attaining complex shapes. Such strict demands require the design of newer engines able to dissipate the heat generated within the combustion chamber to avoid the damage that higher temperatures may cause to the alloy. The work conducted on cast aluminium-silicon alloys to evaluate their thermal diffusivity dependence with respect to temperature, chemical composition, microstructure and heat treatment imparted are presented in this work. The results show how thermal diffusivity can be enhanced by adequate design and proper heat treating practices imposed to the alloy.

Large-Scale Magnetic Field Fragmentation in Flux-Tubes Near the Base of the Solar Convection Zone

Magnetic quenching of turbulent thermal diffusivity leads to instability of the large-scale field with the production of spatially isolated regions of enhanced field. This conclusion follows from a linear stability analysis in the framework of mean-field magnetohydrodynamics that allows for thermal diffusivity dependence on the magnetic field. The characteristic growth time of the instability is short compared to the 11-year period of solar activity. The characteristic scale of the increased field regions measures in tens of mega-meters. The instability can produce magnetic inhomogeneities whose buoyant rise to the solar surface forms the solar active regions. The magnetic energy of the field concentrations coincides in order of magnitude with the energy of the active regions.

Magnetocaloric properties in the Pr0.7Sr0.3-xCaxMnO3: Direct and indirect estimations from thermal diffusivity data

Magnetization, specific heat, thermal diffusivity, and magnetocaloric effect were studied in Pr0.7Sr0.3-xCaxMnO3 system (x = 0; 0.1; 0.2; 0.3) in the temperature range of 80–320 K and in a magnetic field of 18 kOe. A correlation was found between the coefficients under study and microscopic characteristics (〈rA〉 – average ionic radius and σ2 – cationic disorder). The decrease in σ2 and 〈rA〉, caused by the substitution of Sr atoms by Ca atoms, causes a weakening of the exchange interactions and a decrease in ТС. The observed minima in the temperature dependence of thermal diffusivity η(T) near ТС are associated with the appearance of an additional channel of phonon relaxation in fluctuations of the magnetic order parameter. A relationship was found between the MCE value and the change in thermal diffusivity in a magnetic field near ТС. This relationship can be applied as another MCE evaluating indirect method. It is shown that MCE value estimation from thermal diffusivity data is consistent with the results of caloric measurements.

Fractal-based analysis of the void microstructure of Bi2Sr2CaCu2Ox superconducting filaments and the caused anomalous thermal diffusion

High-Tc multifilamentary composites Bi2Sr2CaCu2Ox/Ag/Ag-alloy (Bi2212) are the only round wires (RWs) to be potential candidates for fabricating high field magnets. However, the complicated microstructure of Bi2212 RWs, and especially the Bi2212 filaments, makes deep understanding of the correlation between macroscopic electrothermal behaviors and the microstructure a challenge. Building on our previous work of fractal-based analysis of the Bi2212/Ag interface, in this paper we focus on the void (gas bubble or pore) structure of individual Bi2212 filaments, taking a fractal-based analysis of the void structure and the resulting anomalous thermal diffusion. For fractal characterization of the void structure of Bi2212 filaments, we developed a fractal-based reconstruction model, and further derived a one-dimensional fractional order differential equation with the exponent α (0 < α ≤ 1), which is related to the porosity (0 ≤ ϕ ≤ 1) and fractal dimension (2 < D < 3) of the void structure of Bi2212 filaments. The calculated results show a local anomalous thermal diffusion (quite different from the diffusion in Euclidean homogeneous space corresponding to the materials without any pores), which depends on the porosity and fractal dimension of porous Bi2212 filaments. The dependence of thermal diffusion on the porosity is stronger than on the fractal dimension of the porous structure. This indicates that reducing voids/bubbles in Bi2212 filaments during the heat treatment process is significant for refining thermal diffusion.

Эффективные характеристики теплообмена в пористом слое теплогенератора беспламенного горения

Одним из наиболее распространенных и опасных выбросов, загрязняющих биосферу, являются жидкие углеводородные отходы. В их составе может содержаться более 200 опасных соединений, а колоссальные темпы образования производственных отходов привели к накоплению человечеством более 1 млрд т различных жидких техногенных отходов. В связи с этим назрела проблема утилизации таких жидких отходов, решение которой является одной из приоритетных задач, стоящих перед мировым сообществом. Перспективным направлением в решении этой проблемы является огневая утилизация жидких отходов в беспламенном режиме. Беспламенный режим горения обеспечивается сжиганием жидкого топлива в пористой матрице инертного наполнителя, в качестве которого использован криптол. Актуальной задачей для развития этого научного направлении и конструкторской разработки связанных с ним технических решений является исследование эффективных характеристик криптоловой матрицы. Цель работы: определение теплофизических характеристик углеродной матрицы криптола и получение аналитических зависимостей для инженерных расчетов её предварительного прогрева. Методы исследования: измерение истинных значений теплоемкости и теплопроводности криптола на анализаторе температуропроводности Discovery Flash DLF-1200 в диапазоне температур 298-573 K. Теплофизические процессы при прогреве криптоловой пористой матрицы плоским нагревательным элементом экспериментально исследовались на специально разработанном экспериментальном стенде. Рассмотрено два варианта компоновки стенда: с минимальной и максимальной интенсивностью свободной конвекции воздуха в порах. При математической обработке экспериментальных данных эффективное значение коэффициента температуропроводности выражалось из конечноразностного аналога дифференциального уравнения теплового баланса в нестационарной постановке. Результаты: получены аналитические зависимости эффективного значения температуропроводности от температуры, позволяющие рассчитывать процесс предварительного прогрева криптоловой матрицы с применением дифференциального уравнения теплопроводности, для определения расположения и необходимой мощности нагревательных элементов.

Ultra-pure silicon nanofluid by laser ablation: thermal diffusivity studies using thermal lens technique

Ultra-pure silicon nanoparticles were synthesized through pulsed laser ablation (PLA) in ethanol medium using a Q-switched Nd:YAG nanosecond pulsed laser. Concentration dependence of thermal diffusivity of the silicon nanofluid was studied using dual beam thermal lens technique at room temperature. The thermal diffusivity was found to be decreased with increase in concentration of silicon nanoparticles. This property of nanofluids can be used for thermal trapping and insulating applications.

Thermal properties of pure tungsten and its alloys for fusion applications

Tungsten is a promising candidate for plasma-facing materials in a fusion reactor, and several research studies have been conducted to improve the mechanical properties of pure W. However, the thermal properties are also important characteristics of plasma-facing materials. In this study, the thermal properties of pure W and its alloys were measured, and the effect of alloying on the thermal properties of pure W was investigated. Potassium-bubble (K-bubble) dispersion, which is one of the major methods utilized to improve the mechanical properties of W, did not affect the thermal diffusivity and conductivity of pure W. On the other hand, the presence of rhenium, which is major alloying element of W, affected the absolute values and the temperature dependence of thermal diffusivity and conductivity. The effect of alloying on specific heat and the anisotropy in thermal diffusivity of pure W and its alloys were also investigated. Measurements of the specific heat showed that K-bubble dispersion and Re addition had insignificant effects on the values obtained for pure W. Anisotropy in thermal diffusivity was not observed, and the effect of anisotropic grain structure and alloying was insignificant.