Development of measurement setup for thermal conductivity at high temperatures using the parallel hot-wire

An experimental setup is built to determine the thermal conductivity of a mixture of KNO3 and NaNO3 with a ratio of 54-46m% which is used in high temperature thermal storage systems. The measurement principle is based on the transient parallel hot-wire method which is described in the standards NBN B 62-202 and ISO 8892-2. The setup is designed to measure the thermal conductivity around the melting temperature (<300°C). Measurements within the liquid region show faulty results caused by natural convection within the sample. The measured thermal conductivity within the solid region is 0.5466-0.5529W/mK close to the melting point and 0.7174W/mK at room temperature, which shows a decreasing thermal conductivity with increasing temperature in the solid region.

Correlations among Thermal Conductivity, Porosity, and Permeability of Mesozoic Sandstones and Siltstones from the Southern Regions of the West Siberian Plate

—We consider results of measurements of thermal conductivity, porosity, and permeability for 780 samples of Mesozoic sandstones and siltstones from the cores of 50 wells drilled in three southern regions of the West Siberian Plate (Novosibirsk and Tomsk regions, Surgut region of the Khanty-Mansi Autonomous Area). The thermal conductivity of the samples was measured twice: in dry and in water-saturated states. It has been established that the thermal conductivity of water-saturated rocks is on average 20–40% higher. The thermal conductivities of dry and water-saturated samples show stable correlations between each other and with the sample porosity and permeability. These correlations can be used for the approximate estimation of the thermal conductivity of water-saturated rocks from the measured thermal conductivity of dry samples or even from the porosity values. The relationship between thermal conductivity and porosity can be used for the rapid assessment of rock porosity from the measured thermal conductivity of the core.

Statistical analysis of thermal conductivity experimentally measured in water-based nanofluids

Nanofluids are suspensions of nanoparticles in a base heat-transfer liquid. They have been widely investigated to boost heat transfer since they were proposed in the 1990s. We present a statistical correlation analysis of experimentally measured thermal conductivity of water-based nanofluids available in the literature. The influences of particle concentration, particle size, temperature and surfactants are investigated. For specific particle materials (alumina, titania, copper oxide, copper, silica and silicon carbide), separate analyses are performed. The conductivity increases with the concentration in qualitative agreement with Maxwell’s theory of homogeneous media. The conductivity also increases with the temperature (in addition to the improvement due to the increased conductivity of water). Surprisingly, only silica nanofluids exhibit a statistically significant effect of the particle size, whereby smaller particles lead to faster heat transfer. Overall, the large scatter in the experimental data prevents a compelling, unambiguous assessment of these effects. Taken together, the results of our analysis suggest that more comprehensive experimental characterizations of nanofluids are necessary to estimate their practical potential.

Evaluation of Interfacial Thermal Resistance of Al-AlN Composites by Using Image-Based Calculation

Interfacial thermal resistance of Al-AlN composites was evaluated by comparing the measured thermal conductivity and the simulated thermal conductivity. Al-10vol.%AlN and Al-20vol.%AlN composites were fabricated by spark plasma sintering. Effective thermal conductivity was measured with the steady state thermal conductivity measuring device. Effective thermal conductivity was also simulated by using FE-SEM image and the measured relative density. Comparing the measured thermal conductivity and the simulated thermal conductivity, interfacial thermal resistance in Al-AlN composites was evaluated as about 1.27-6.2510-9 m2K/W.

Особенности теплопереноса в гетероструктурах Al-=SUB=-x-=/SUB=-Ga-=SUB=-1-x-=/SUB=-N/GaN на сапфире

Thermal conductivity of thin layers of AlxGa1-xN/GaN (0.05≤ x≤1) heterostructures on sapphire grown with molecular beam epitaxy has been measured. Thermal conductivity values of AlxGa1-xN и GaN thin films at room temperature have been obtained. Concentration dependence of thermal conductivity has been analyzed with the virtual crystal thermal conductivity model. Thermal transport in the structure considering local heating has been simulated numerically in order to find optimal structure layers` thicknesses allowing high thermal conductivity value.

Evaluation of Effective Thermal Conductivity of Metal Matrix Composites by Using Image-Based Calculation

Interfacial thermal resistance in Al-SiC composites was evaluated by comparing the measured thermal conductivity and the calculated thermal conductivity. Al-20vol.%SiC composites changing SiC particle size, 3 μm to 30 μm, was fabricated by spark plasma sintering and heat treatment. Effective thermal conductivity was measured with the steady state thermal conductivity measuring device. Effective thermal conductivity was also calculated by using SEM image and the measured relative density. Comparing the measured thermal conductivity and the calculated thermal conductivity, interfacial thermal resistance in Al-SiC composites was evaluated as about 1.0x10-8 (m2K)/W.

Thermal Resistance of Polystyrene-Seeded Concrete for Better Insulative Value

This paper details the experimentally-measured thermal conductivity, k, of concrete composite samples consisting of various mixtures of extruded polystyrene waste chips and concrete for the purpose of better insulative value and lighter weight. A “hot box” apparatus was designed based on the parameters of ASTM C1363, and was constructed primarily out of 4” rigid polystyrene insulation and designed to force the majority of the heat generated in the enclosure through the test samples. The design allowed for the indirect measurement of thermal conductivity, k, by directly measuring the internal and external surface temperatures of the samples and heat input required to maintain a steady state internal temperature. Several samples with well documented k values were first tested to calibrate the hot box apparatus. Prototype samples were made in sheets and also in cylindrical format to test for thermal conductivity and also compression testing, respectively. Results showed that although the insulative values of the concrete composite increased with additional polystyrene aggregate, as would be expected, at some point there is a rapid fall-off in compressive strength.

Intertwined orders in heavy-fermion superconductor CeCoIn5

We use thermal conductivity to study a unique state in the high field corner of the superconducting phase of CeCoIn5. The spin-density-wave (SDW) magnetic order in this high field low temperature (HFLT) phase requires superconductivity for its very existence, and both magnetism and superconductivity disappear together at superconducting critical field H[Formula: see text]. We measured thermal conductivity of CeCoIn5 in a rotating magnetic field to study the nature of the HFLT phase. Our measurements reveal the presence of an additional order inside the HFLT phase that is intimately intertwined with the superconducting [Formula: see text]-wave and the SDW orders, which we identify as a superconducting [Formula: see text]-wave pair-density-wave (PDW). CeCoIn5 displays a hierarchy of interactions within the HFLT phase, where spin–orbit coupling orients the SDW, which then determines orientation of the secondary PDW component.

THERMAL PERFORMANCE OF PANELS WITH HIGH DENSITY, RANDOMLY ORIENTED STRAW BALES

This paper describes the hot-box testing (based on ASTM C1363-11) of seven straw bale wall panels to obtain their thermal conductivity values. All panels were constructed with stacked bales and cement-lime plaster skins on each side of the bales. Four panels were made with traditional, 2-string field bales of densities ranging from 89.5 kg/m3–131 kg/m3 and with the bales on-edge (fibres perpendicular to the heat flow). Three panels were made with manufactured high-density bales (291 kg/m3–372 kg/m3). The fibres of the manufactured bales were randomly oriented. The key conclusion of this paper is that within the experimental error, there is no difference in the thermal conductivity value for panels using normal density bales and manufactured high density bales up to a density of 333 kg/m3. However, because of lack of precision of the hot-box, no conclusions can be made on the true thermal conductivity of the high density bale panels. In addition, the panels tested were found to have significant voids between bales, and this is believed to have contributed to higher measured thermal conductivity values compared to those reported in the literature for normal density bale panels. Thermal properties may be affected for bales with higher densities than 333 kg/m3, therefore further testing is suggested.