Thermal diffusivity measurements on Zirconium-based cladding materials have historically been a challenge due to the difficulty to measure on specimens with curved geometries, including nuclear grade ...Zircaloy cladding materials. Here, in this work, we first used laser flash analysis method and four-probe configuration method to measure the thermal diffusivity and electrical resistivity of Zircaloy tubes respectively, which show good agreement with Zircaloy plates in this work, as well as previously published data. The consistent results proved the applicability of the laser flash analysis setup and four-probe configuration method for investigating thermal diffusivity and electrical resistivity of Zircaloy tubes. We further investigated the hydrogen effect on thermal diffusivity and electrical resistivity of Zircaloy. Hydrogen plays significant roles in the thermal diffusivity of Zircaloy, which depends on the hydrogen concentration. For higher hydrogen contents (1130 and 1820 wppm in this work), where phase transformation (α-Zr + δ-hydride → α-Zr + β-Zr) occurs at 567 °C, thermal diffusivity decreases as a function of temperature at the α-Zr + δ-hydride phase regime, while increase at higher temperature at the α-Zr + β-Zr phase regime. For low hydrogen concentration, where hydride dissolved into α-Zr matrix phase at higher temperature, the thermal diffusivity is lower than non-hydrided Zircaloy-4 with similar temperature-dependent trends. Such observation demonstrates the hydrogen effects on reducing thermal diffusivity of α-Zr phase. Hydrogen increases the electrical resistivity of Zircaloy. Similar to thermal diffusivity results, the phase transformation causes a reversal of temperature-dependent trends in electrical resistivity results in Zircaloy-4 with higher hydrogen contents.
•Volatiles variations were inversely related with changes of fixed carbon.•A factor analysis method combining qualitative and quantitative was proposed.•Heat transfer mechanism of coal low ...temperature oxidation process was investigated.•Correlation between thermal properties and proximate analysis was approached.
The low temperature oxidation of coal is a contradictory and unified dynamic process of coexisting mass and heat transfer. The thermophysical properties are crucial during coal spontaneous combustion. In the current paper, the variations of moisture, ash, volatiles, fixed carbon and thermophysical properties (thermal diffusivity, specific heat and thermal conductivity) of three coal samples from 30 °C to 300 °C were studied, and their grey correlation was analyzed. The results indicated that with the increase of temperature, the free moisture of Coals A and B decreased first but then increased, while the free moisture of Coal C kept decreasing without a later increase. The variation of surface moisture was consistent with that of free moisture. The trend of volatiles and fixed carbon was completely the opposite, showing a significant negative correlation. Ash was less affected by temperature. Along with the rise of temperature, the thermal diffusivity of three coal samples decreased first but later increased, and the specific heat was always in a state of increasing. The change in thermal conductivity was mainly affected by specific heat. By calculating the grey correlation degree, the major factors affecting the thermophysical properties were obtained.
In this work, a microfabricated chip device for measurement of in-plane thin film thermal diffusivity by temperature wave analysis (TWA) is presented. The device consists of a suspended silicon ...nitride (SiNx) membrane with a micro-patterned electric Joule heater in the center and several temperature sensors at different distances from the center. The SiNx membrane serves as a thermally isolated platform for the thin film of interest. The design of the measurement device and its fabrication process are presented. Temperature calibration of the RTDs and measurement of the steady-state temperature rise on the membrane were carried out. Finally, the thermal diffusivity of the bare chip and the bare chip coated with polymeric Parylene C thin films of different thicknesses was measured by a temperature wave method. The steady state temperature and temperature wave measurement were performed in high vacuum (p < 1 ×10−5 mbar). For the 150 nm thick low stress SiNx membrane, a thermal diffusivity of (1.77 ± 0.10)× 10−6 m2 s−1 was measured. The device is sensitive to differences in the thermal diffusivity resulting from changes in Parylene C layer thickness of a few hundred nanometers.
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•Development of a general-purpose thermal measurement device for micro samples.•Design and fabrication of a multi-distance micro-Joule heater and temperature sensor array with high spatial resolution.•Samples can be deposited after fabrication by simple means of spin coating, PVD, CVD techniques prior to the measurement.•In-plane thermal diffusivity measurement of a 150 nm SiNx membrane and Parylene C nanofilms by Temperature Wave Analysis.
The PBF-LB/M process is highly suitable for the additive manufacturing of complex parts with precise geometrical accuracy using metallic powders. However, certain unknown variables exist within the ...process. Particularly, the thermal conductivity introduces a significant level of uncertainty due to the substantial impact of heat transfer from the part solid to the bulk material. Insufficient experimental data on the thermophysical properties of powder and a limited understanding of the influencing factors further exacerbate this issue. This study presents the thermophysical properties of steel powders commonly employed in the PBF-LB/M process, utilizing a newly-developed powder container for laser flash analysis. Through a quantitative comparative analysis with the corresponding solid materials, it has been demonstrated that the chemical composition and microstructure play a secondary role in determining the heat conductivity of the powder bed. Instead, it is the powder size distribution that serves as the primary parameter governing the observed behavior.
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•Thermophysical properties of powder were measured by dynamic measurement method.•A novel measurement device for powder measurements using laser-flash was used.•Powder properties differ significantly from corresponding solid properties.•Particle size is the main influence on the thermophysical properties.
Cubes and spheres of spruce wood have been prepared, with a fine thermocouple inserted to measure the temperature at their centre. Individual particles were immersed rapidly in a bed of sand (mean ...size ∼0.2 mm), which was fluidised by nitrogen and held at a fixed temperature up to 700 °C. The rising temperature measured at a particle's centre yielded the effective value of the particle's thermal diffusivity. The temperature response showed evidence of at least two endothermic decomposition reactions, which corresponded to the pyrolysis of fine particles of the wood in a thermogravimetric analyser (TGA). However, the wood undergoing thermal decomposition in a fluidised bed at 500 °C revealed at least one exothermic step at the very end of heating. After being heated this way in a hot bed fluidised by nitrogen, the particles of char formed by spruce wood had very much the same size and shape as the original piece of wood before being heated. These new particles of “char”, formed whilst being heated in a hot fluidised bed, were cooled in a stream of nitrogen and returned to the fluidised bed for re-heating without any complications from pyrolysis. The rise in the char's central temperature with time gave an unambiguous value for the thermal diffusivity of the char. It is clear that volatile matter leaving a particle of wood reduced the rate of heat transfer between a hot fluidised bed and the centre of a devolatilising particle. Also, the time for complete pyrolysis was proportional to the square of the characteristic size (r0) of the spruce being heated. In addition, the time for pyrolysis was proportional to Tbed3±1, so that for a cube of spruce tpyr = 2.9 ± 0.3 × 1015r02/Tbed3 in seconds. Photographic evidence confirmed that devolatilisation of particles of spruce larger than ≈ 2 mm in a fluidised bed follows a shrinking core model and is accordingly controlled by internal heat transfer.
The knowledge of the thermal conductivity of nuclear fuel and its evolution as a function of temperature and burn up is a major challenge in the context of the evaluation and understanding of ...irradiated fuel performances in current reactors. It is also the case for the development and qualification of fuel for future reactors. Indeed, numerical simulations of the fuel behaviour under various conditions require the accurate knowledge of thermal conductivity over a wide range of temperature (from ambient to melting point temperature) but also at the scale of few tens of micrometres to take into account the microstructural effects on the thermomechanical evolution of the fuel in normal or incidental irradiation conditions. Different methods, using laser matter interactions, can deduce the thermal conductivity from a thermal diffusivity measurement. In this paper, the potential of two techniques, which present spatial resolution from millimetre to few tens microns, are discussed in the context of the determination of the fuel thermal conductivity: laser flash method and infrared microscopy. Experiments on graphite, as material model, have been conducted and validate these two thermal diffusivity measurement techniques. We present a measurement example for both methods on graphite and then a first experiment carried out with the infrared microscopy technique on UO2.
Understanding the effect of grain size on the overall electrical and thermal transport properties of PRGO films on a large scale is not only fundamental but also technologically important in order to ...tune their properties for wide applications. In this work, by adjusting the annealing temperature, we control the density of the oxygen containing functional groups and thus the structural domain size of PRGO film. The annealing effect on the temperature dependency of thermal and electrical transport is studied. In addition, the linear relationship between thermal diffusivity and electrical conductivity is confirmed from 320 K to 10 K. The temperature dependent thermal diffusivity of the amorphous region in PRGO is reported. In the last, based on the residual thermal reffusivity at 0 K limit, the structure defects induced phonon mean free path against the annealing temperature is obtained, and compared with the cluster size calculated from XRD, TEM and Raman. A linear relationship among the structure domain size, thermal diffusivity, and electrical conductivity is further revealed, which demonstrates the strong effect of structure domain size on the thermal and electrical transport of PRGO.
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•A linear relationship between the thermal diffusivity and electrical conductivity from 320 K to 10 K is reported in PRGO films with varying reduction level. The corresponding mathematical model is proposed.•The electrical transport is found to vary with the thermal reduction level, where the temperature coefficient of resistance (TCR) decreases as the annealing temperature increases, reflecting a tunable band gap.•Based on the residual thermal reffusivity at 0 K limit, the structure defects induced phonon mean free path against the annealing temperature is obtained, and compared with the cluster size calculated from XRD and Raman.•A linear relationship among the structure domain size, thermal diffusivity, and electrical conductivity is further revealed.
•Critical properties, heat capacities, and thermal diffusivities were measured.•The thermal conductivities of the compounds under study were calculated.•Thermal properties were determined for liquid ...phase at atmospheric pressure.•The compounds under study are second-generation biofuels and intermediates.
The critical temperatures, critical pressures, heat capacities, and thermal diffusivities have been measured for furfural, furfuryl alcohol, furfuryl acetate, and tetrahydrofurfuryl alcohol, the compounds of industrial importance because they are involved in the production of biofuels. The critical properties have been measured using the pulse-heating method applicable to thermally unstable compounds. The relative combined expanded uncertainties with the 0.95 level of confidence are 0.01 and 0.03 for the critical temperature and pressure of furfural and furfuryl acetate and 0.015 and 0.04 for furfuryl alcohol and tetrahydrofurfuryl alcohol. The acentric factors of the compounds have been calculated based on the experimental data. The critical properties of the compounds have also been calculated by the group contribution methods of Wilson and Jasperson, Nannoolal et al. Marrero and Gani, Hukkerikar et al. in two variants. The Wilson and Jasperson and Nannoolal et al. techniques provide the best estimation of the critical temperature; for the critical pressure, the Nannoolal et al. method gives the best results. The heat capacities in the liquid phase have been measured at atmospheric pressure in the temperature range from 298.15 to 451.15 K by DSC technique with relative combined expanded uncertainty 0.03. The data obtained have been approximated by third-order polynomials. The experimental heat capacities have been compared with those calculated by the group-contribution method of Kolska et al. The thermal diffusivities have been measured by laser flash method at atmospheric pressure in the temperature range from 313.15 to 373.15 K with relative combined expanded uncertainty 0.05. The experimental data have been approximated by first-order polynomials. The thermal conductivities have been calculated using the experimental data obtained.
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