We study the thermal diffusivity DT in models of metals without quasiparticle excitations (“strange metals”). The many-body quantum chaos and transport properties of such metals can be efficiently ...described by a holographic representation in a gravitational theory in an emergent curved spacetime with an additional spatial dimension. We find that at generic infrared fixed points DT is always related to parameters characterizing many-body quantum chaos: the butterfly velocity vB and Lyapunov time τL through DT∼vB2τL. The relationship holds independently of the charge density, periodic potential strength, or magnetic field at the fixed point. The generality of this result follows from the observation that the thermal conductivity of strange metals depends only on the metric near the horizon of a black hole in the emergent spacetime and is otherwise insensitive to the profile of any matter fields.
We investigated thermal properties of the epoxy-based composites with the high loading fractionup to f ≈ 45 vol %of the randomly oriented electrically conductive graphene fillers and electrically ...insulating boron nitride fillers. It was found that both types of the composites revealed a distinctive thermal percolation threshold at the loading fraction fT > 20 vol %. The graphene loading required for achieving thermal percolation, fT , was substantially higher than the loading, fE , for electrical percolation. Graphene fillers outperformed boron nitride fillers in the thermal conductivity enhancement. It was established that thermal transport in composites with high filler loadings, f ≥ fT , is dominated by heat conduction via the network of percolating fillers. Unexpectedly, we determined that the thermal transport properties of the high loading composites were influenced strongly by the cross-plane thermal conductivity of the quasi-two-dimensional fillers. The obtained results shed light on the debated mechanism of the thermal percolation, and facilitate the development of the next generation of the efficient thermal interface materials for electronic applications.
The Cover Feature shows impurities and functional groups on graphene flake surfaces being removed by photons. Under photon irradiation, both thermal chemical reduction and photo‐chemical reduction ...take place, and such processes are probed dynamically by thermal and electrical characterizations. Photo‐reduction provides down to sub‐micron resolution structure tailoring for graphene aerogels. Cover design by Dr. Xinwei Wang. More information can be found in the Research Article by Yangsu Xie, Xinwei Wang and co‐workers.
A novel high‐entropy carbide ceramic, (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C, with a single‐phase rock salt structure, was synthesized by spark plasma sintering. X‐ray diffraction confirmed the formation of a ...single‐phase rock salt structure at 26‐1140°C in Argon atmosphere, in which the 5 metal elements may share a cation position while the C element occupies the anion position. (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C exhibits a much lower thermal diffusivity and conductivity than the binary carbides HfC, ZrC, TaC, and TiC, which may result from the significant phonon scattering at its distorted anion sublattice. (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)C inherits the high elastic modulus and hardness of the binary carbide ceramics.
A spot periodic heating method is a highly accurate, non-contact method for the evaluation of anisotropy and relative thermophysical property distribution. However, accurately evaluating thermal ...diffusivity is difficult due to the influence of temperature wave reflection from the whole surface of the sample. This study proposes a method to derive thermal diffusivity using a parameter table based on heat transfer equations using the concept of optimum distance between heating-point and measurement point. This method considers finite sample size, sensitivity distribution of infrared ray detector, intensity distribution of heating laser and sample thickness. In these results, the obtained thermal diffusivity of pure copper corresponded well with previous literature values. In conclusion, this method is considered highly effective in evaluating the thermal diffusivity in the horizontal direction.
•Critical properties, heat capacities, and thermal diffusivities were measured.•Measurements were performed for liquid α-angelica lactone and triacetin.•The thermal conductivities of the compounds ...under study were calculated.•The compounds under study are involved in the production of fuels and fuel additives.
The critical temperatures, critical pressures, heat capacities, and thermal diffusivities of α-angelica lactone and triacetin have been measured. The compounds under study are involved in the production of fuels and fuel additives from lignocellulose. The critical properties of the compounds have also been calculated by the group contribution methods of Wilson and Jasperson (WJ), Nannoolal et al. (NRR), Marrero and Gani, Hukkerikar et al. in two variants (H-sw and H-s). The NRR method provides the best estimation of the critical temperature and pressure of α-angelica lactone: the differences between experimental and estimated values are about 1.6 and 3.0 %, respectively. For triacetin, all the methods used give approximately the same discrepancy between the experimental and estimated critical temperature in the range from 1.2 to 2.0 % which is less than the uncertainty of the measurement. However, the H-s and H-sw techniques slightly overestimate the critical temperature, while the rest of the methods underestimate it. All the methods overestimate the critical pressure of triacetin; the H-s method provides the minimum difference between the measured and calculated values of the critical pressure (1.3 %).
The heat capacities of liquid α-angelica lactone and triacetin have been measured at atmospheric pressure in the temperature range from 298.6 to 440.6 K (α-angelica lactone) and from 298.4 to 530.2 K (triacetin). The data obtained have been fitted with first-order polynomials. The heat capacities of the compound under study have also been estimated using the group-contribution method of Kolska et al. This method has been recommended to estimate the heat capacities of α-angelica lactone and triacetin.
The thermal diffusivities of liquid α-angelica lactone and triacetin have been measured at atmospheric pressure in the temperature range from 303.15 to 373.15 K. The thermal conductivities have been calculated from the results of the experiment. The experimental data on thermal diffusivity and thermal conductivity have been approximated with linear polynomials. The thermal conductivities of α-angelica lactone and triacetin have been calculated by the methods of Govender et al. and Sastri. In general, the method of Govender et al. gives thermal conductivity values of the compounds under study that are closer to the experimental values than those obtained using the Sastri method.
To better understand the changes in the hydrologic cycle caused by global warming in Antarctica, it is crucial to improve our understanding of the groundwater flow system, which has received less ...attention despite its significance. Both hydraulic and thermal properties of the active layer, through which groundwater can flow during thawing seasons, are essential to quantify the groundwater flow system. However, there has been insufficient information on the Antarctic active layer. The goal of this study was to estimate the hydraulic and thermal properties of Antarctic soils through laboratory column experiments and inverse modeling. The column experiments were conducted with sediments collected from two lakes in the Barton Peninsula, Antarctica. A sand column was also operated for comparison. Inverse modeling using HydroGeoSphere (HGS) combined with Parameter ESTimation (PEST) was performed with data collected from the column experiments, including permeameter tests, saturation-drain tests, and freeze-thaw tests. Hydraulic parameters (i.e., Ks, θs, Swr, α, β, and Ss) and thermal diffusivity (D) of the soils were derived from water retention curves and temperature curves with depth, respectively. The hydraulic properties of the Antarctic soil samples, estimated through inverse modeling, were 1.6 × 10−5–3.4 × 10−4 cm s−1 for Ks, 0.37–0.42 for θs, 6.62 × 10−3–1.05 × 10−2 for Swr, 0.53–0.58 cm−1 for α, 5.75–7.96 for β, and 5.11 × 10−5–9.02 × 10−5 cm−1 for Ss. The thermal diffusivities for the soils were estimated to be 0.65–4.64 cm2 min−1. The soil hydraulic and thermal properties reflected the physical and ecological characteristics of their lake environments. The results of this study can provide a basis for groundwater-surface water interaction in polar regions, which is governed by variably-saturated flow and freeze-thaw processes.
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•Hydraulic and thermal properties of an Antarctic active layer were determined.•Column experiments and inverse modeling were conducted to derive soil properties.•The properties reflected the characteristics of Antarctic lake environments.•This study helps understanding variably-saturated flow and freeze-thaw processes.
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•The thermal properties of coal at cryogenic conditions (−100 to 0 °C) is investigated.•The thermal diffusivity of coal increases by 121.4 % with decreasing temperature.•The specific ...heat capacity of coal decreases by 57.9–65.9 % with decreasing temperature.•The volatile matter and carbon content in coal have the highest correlation with thermal properties (∼0.9).•The thermal diffusivity of coal increases with increasing volatile matter content but decreases with increasing carbon content.
The thermal properties of coal are important factors that influence the heat and mass transfer during the pyrolysis process. Therefore, thermal properties were investigated for two tar-rich coal under cryogenic temperature and pyrolysis condition using laser flash analyzer. Gray correlation analysis and chemical composition analysis are combined to analyze the impact of chemical properties on thermal properties. With decreasing temperature, the thermal diffusivity of coal experiences a significant increase by 108.9–121.4 %, while the specific heat capacity decreases by 57.9–65.9 %. The volatile matter and fixed carbon content in tar-rich coal have the highest correlation with thermal properties (∼0.9), followed by moisture content (∼0.62), while the ash content has the lowest correlation with thermal properties (∼0.5). The thermal diffusivity of tar-rich coal increases with increasing volatile matter content. Furthermore, within the range of −100 °C to 300 °C, the thermal diffusivity of tar-rich coal decreases with increasing carbon content, while the specific heat capacity increases with increasing carbon content. The results indicate that under low-temperature cryogenic conditions, the internal heat transfer capability of tar-rich coal is significantly improved.
Variation of the cumulative heat stored in n-hexadecane (C16), n-heptadecane (C18) and n-eicosane (C20) as function of temperature. Display omitted
•Thermal properties of n-hexadecane, n-octadecane ...and n-eicosane used as PCM are reported.•Thermal conductivity and thermal diffusivity were measured by the hot wire technique at different temperatures.•A discontinuity in thermal conductivity and diffusivity was detected near the melting temperature.•No literature data were found for the thermal diffusivity of the three n-alkanes considered in this study.•The cumulative heat stored increases with the number of carbon in the n-alkane hydrocarbon chain.
The thermal conductivity (λ) and thermal diffusivity (aT) of the solid/liquid phase change linear n-alkanes were measured simultaneously by the transient multi-current hot wire technique at atmospheric pressure in the range 258–348K. The same set-up was used to measure λ and aT of the liquid and the solid states at different electrical currents. Three n-alkanes, n-hexadecane (C16H34), n-octadecane (C18H38) and n-eicosane (C20H42) were studied. Differential scanning calorimetry was applied at the temperature range 248–348K to determine the melting/crystallization temperature, the heat of melting/crystallization and the specific heat of both the solid and liquid phases. Some results were compared with available literature data. The density of the n-alkanes at liquid state was also measured at different temperatures and their thermal diffusivity was estimated and compared to that obtained by the hot wire technique. The cumulative energy stored was estimated over a definite range of temperature for the three n-alkanes and this was found to be higher for eicosane.
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