Magnitude Of Thermal Conductivity Research Articles

Effect of Vanadium Doping on Thermoelectric Properties of CaMnO<sub>3</sub> Using First Principle Calculations

The search for clean energy conversion technologies promotes the study of thermoelectric materials. In this paper, the electronic structure and thermoelectric properties of CaMnO3 doped with 17% V using first principles calculations and semi-classic Boltzmann theory on Ca site as well as Mn sites. The G-type AFM magnetic ordering is most stable among four types of magnetic ordering for CaMnO3 and V doped CaMnO3 a Mn site while FM ordering was found for V doped CaMnO3 at Ca site. The calculated partial density of states plot shows half metallic and metallic behavior for V doped at A site and B site respectively. Thermoelectric property calculations show that the magnitude of Seebeck coefficient decreased with V doping at both sites with V doping at Mn sites has the lowest magnitude of Seebeck coefficient. All samples show the negative Seebeck coefficient indicating n type behavior. The magnitude of conductivity increases with V doping with the highest magnitude belong to V doped at Mn site. The magnitude of thermal conductivity also increased with V doping at Mn site, but shows a reduction for V doping at Ca site. The figure of merit (ZT) for V doping at Ca site shows a significant improvement over intrinsic CaMnO3 at 0.14 at 1000 K. However, V doping at Mn site sample shows a reduction of ZT at 0.0028 for CaMnO3 at 1000 K which is much lower than CaMnO3 at 0.08.

Tunable thermal conductivity and rheology of in-house synthesized Fe55Co25Ni20 complex fluids under the external magnetic field

In the present investigation, trimetallic (FeCoNi) nanoparticles have been successfully synthesized in water (solvent) though reductive emulsion technique in the size range 10–15 nm and magnetic saturation 63 emu/g. The synthesized nanoparticles have been utilized to fabricate two types of nanofluids by using two different base mediums, namely; heat transfer oil (HTO) and ethylene glycol (EG). Experimental investigations show that the magnitude of thermal conductivity, viscosity and yield stress of the fabricated nanofluids are amplified under the influence of external magnetic field. The highest amplification in the magnitude of thermal conductivity is achieved ~0.555 W/mK and the respective augmentation for the same with respect to base nanofluid (in the absence of magnetic field) is observed ~77% at critical magnetic field 800 G and 5 vol% particles loading for the sample of FeCoNi/HTO. Moreover, maximum value of static yield stress and viscosity for the same sample are found ~7.4 kPa and ~1.9 kPa.s at 12000 G respectively. The fabricated nanofluids demonstrate excellent reversible behavior under the varying magnetic field. The findings of present investigations have utility in various fields such as automotive damping, MR brakes and clutches, hydraulic couplings etc. where thermal conductivity, viscosity as well as yield sress play an important role.

Maneuvering thermal conductivity of magnetic nanofluids by tunable magnetic fields

We report an experimental investigation of magnetic field dependent thermal conductivity of a transformer oil base magnetic fluid as a function of volume fractions. In the absence of magnetic field, thermal conductivity increases linearly with an increase in volume fraction, and magnitude of thermal conductivity thus obtained is lower than that predicted by Maxwell's theory. This reveals the presence of clusters/oligomers in the system. On application of magnetic field, it exhibits a non-monotonous increase in thermal conductivity. The results are interpreted using the concept of a two-step homogenization method (which is based on differential effective medium theory). The results show a transformation of particle cluster configuration from long chain like prolate shape to the aggregated drop-like structure with increasing concentration as well as a magnetic field. The aggregated drop-like structure for concentrated system is supported by optical microscopic images. This shape change of clusters reduces thermal conductivity enhancement. Moreover, this structure formation is observed as a dynamic phenomenon, and at 226 mT field, the length of the structure extends with time, becomes maximum, and then reduces. This change results in the increase or decrease of thermal conductivity.

21pm3-PM021 電子線照射により歪みを付加したビスマステルル薄膜の熱輸送特性

In order to investigate the thermal transport properties of strained bismuth telluride thin films, we carried out an electron beam (EB) irradiation to the thin films, and then measured the thermal conductivity by 3ω method. It was found that the crystallinity was dependent upon the EB irradiation dose whereas the crystal orientation of thin films was not affected. The lattice constants of a- and c-axis were shifted slightly with increasing the EB irradiation dose. Finally, The thermal conductivity of thin films was influenced strongly with the EB irradiation but the relationship between the magnitude of thermal conductivity and dose of EB irradiation was not clear yet.

Frost halos from supercooled water droplets

Water freezing on solid surfaces is ubiquitous in nature. Even though icing/frosting impairs the performance and safety in many processes, its mechanism remains inadequately understood. Changing atmospheric conditions, surface properties, the complexity of icing physics, and the unorthodox behavior of water are the primary factors that make icing and frost formation intriguing and difficult to predict. In addition to its unquestioned scientific and practical importance, unraveling the frosting mechanism under different conditions is a prerequisite to develop "icephobic" surfaces, which may avoid ice formation and contamination. In this work we demonstrate that evaporation from a freezing supercooled sessile droplet, which starts explosively due to the sudden latent heat released upon recalescent freezing, generates a condensation halo around the droplet, which crystallizes and drastically affects the surface behavior. The process involves simultaneous multiple phase transitions and may also spread icing by initiating sequential freezing of neighboring droplets in the form of a domino effect and frost propagation. Experiments under controlled humidity conditions using substrates differing up to three orders of magnitude in thermal conductivity establish that a delicate balance between heat diffusion and vapor transport determines the final expanse of the frozen condensate halo, which, in turn, controls frost formation and propagation.

Improved 3-omega measurement of thermal conductivity in liquid, gases, and powders using a metal-coated optical fiber

A novel 3ω thermal conductivity measurement technique called metal-coated 3ω is introduced for use with liquids, gases, powders, and aerogels. This technique employs a micron-scale metal-coated glass fiber as a heater/thermometer that is suspended within the sample. Metal-coated 3ω exceeds alternate 3ω based fluid sensing techniques in a number of key metrics enabling rapid measurements of small samples of materials with very low thermal effusivity (gases), using smaller temperature oscillations with lower parasitic conduction losses. Its advantages relative to existing fluid measurement techniques, including transient hot-wire, steady-state methods, and solid-wire 3ω are discussed. A generalized n-layer concentric cylindrical periodic heating solution that accounts for thermal boundary resistance is presented. Improved sensitivity to boundary conductance is recognized through this model. Metal-coated 3ω was successfully validated through a benchmark study of gases and liquids spanning two-orders of magnitude in thermal conductivity.

Thermal conductivity of silver doped lanthanum manganites between 10 and 300 K

Thermal conductivity ( λ) of nanocrystalline La 1− x Ag x MnO 3 ( x=0.05, 0.15, 0.25, 0.3) pellets prepared by pyrophoric method is reported between 10 and 300 K. Magnitude of thermal conductivity has been found to be strongly influenced by monovalent (Ag) substitution at the La site. Silver doping in LaMnO 3 enhances T C of the system to ∼299 K. Qualitative nature of the temperature variation of thermal conductivity of the silver substituted lanthanum manganites remains closely similar to that for divalent doped systems. Our analysis demonstrates that in La 1− x Ag x MnO 3 also, the mechanism of heat conduction is predominantly by phonons. The contribution of the electronic part is only ∼1% of the total λ. The spin wave contribution is also estimated close to T C, which for all the samples lies within ∼2%. At temperatures below ∼100 K, the measured data have been analyzed using phonon relaxation time method and the strengths of the various phonon scattering processes have been estimated. Our analysis further suggests strong influence of phonon scattering by 2D like defects in the thermal conductivity of monovalent doped lanthanum manganites at low temperatures (<70 K) in the ferromagnetic region.

Synthesis and characterization of Er-substituted Bi-2223 H-Tc glass–ceramic superconductors

The Bi2Sr2Ca2Cu3−xErxO10+δ (x = 0.5 and 1.0) H-Tc system was prepared by glass–ceramic technique to investigate the microstructural formation, thermal and transport properties. We have found that Er+3 ions have a solid solubility limit in the Bi-2223 system and this limit was passed at x = 1.0. Below this limit glass samples were prepared and converted to the glass–ceramic form easily, but after the solid solubility limit glass formation was diminished and crystallized samples were formed after melt quenching. The substitution had considerable effect on the electrical properties comparing with the unsubstituted Bi-2223 material. The Tc values of the x = 0.5 and 1.0 sample were found to be 71 ± 0.1K. The thermoelectric power data were analyzed in view of “two band model with linear T-term” and “Xin’s two band model”. Thermoelectric power was obtained to be positive for the both samples, indicating that the hole type conductivity is dominant in the materials prepared. The magnitude of thermal conductivity, κ, was also influenced by the Er concentration. When the Er concentration was increased the magnitude of κ was suppressed. It strongly indicates that the impurities play a significant role in limiting the heat transport due to a strong increase of the electron–phonon-impurity scattering rate.

Thermal conductivity of La 0.67(Ca xSr 1− x) 0.33MnO 3 ( x=0, 0.5, 1) and La 0.6Y 0.07Ca 0.33MnO 3 pellets between 10 and 300 K

Thermal conductivity ( λ) of nanocrystalline La 0.67(Ca x Sr 1− x ) 0.33MnO 3 ( x=0, 0.5, 1) and La 0.6Y 0.07Ca 0.33MnO 3 pellets prepared by a novel ‘pyrophoric’ method have been studied between the temperature range 10 and 300 K. Our data show that the magnitude of thermal conductivity is strongly influenced by the ion substitutions at La-site. The analysis of the thermal conductivity data indicates that the thermal transport is governed largely by phonons scattering in these systems and the electronic contribution is as small as 0.2–1% of total thermal conductivity ( λ total). At low temperatures (<90 K) 2D like lattice defects contribute to the phonon scattering dominantly and its strength increases with increasing Sr content and also with partial substitution of La by Y. Depending upon the composition of the samples, the magnon thermal conductivity contributes 2–15% of λ total close to T C. In the paramagnetic regime the unusual increase in λ total keeps signature of large dynamic lattice distortion.

Thermal Conductivity in &lt;I&gt;X&lt;/I&gt;&lt;SUB&gt;2&lt;/SUB&gt;&lt;I&gt;YZ&lt;/I&gt; Heusler Type Intermetallic Compounds

Results are given of comprehensive measurements on thermal conductivity of Heusler type intermetallic compounds Fe2AlTi, Co2AlTi, Ni2AlTi, Ni2GaTi, Ni2AlZr and Ni2AlHf. The compounds have fully ordered L21 structure. There exists a wide single phase region of L21 in Ni–Al–Ti ternary alloy system. The contour map showing the magnitude of thermal conductivity is constructed in Ni2AlTi single phase region. The thermal conductivity in Ni2AlTi takes a maximum of 21.4 Wm−1K−1 at stoichiometry which is much lower than that of NiAl having a B2 structure. By the deviation from stoichiometry, the thermal conductivity decreases in Heusler compounds. The magnitude of thermal conductivity in Fe2AlTi, Co2AlTi and Ni2AlTi are compared in connection with those of B2 aluminides (FeAl, CoAl, NiAl) and titanides (FeTi, CoTi, NiTi). Thermal conductivities in three kinds of Heusler compounds X2AlTi (X: Fe, Co, Ni) are almost the same value of approximately 20 Wm−1K−1. Ordering from B2 to L21 incrcases thermal conductivity in accord with the estimation by Nordheim relation. The magnitude of thermal conductivity in X2YZ Heusler compounds, including Ni2GaTi, Ni2AlZr and Ni2AlHf, is related to those of XY and XZ compounds having a B2 structure.

Giant Magnetic Field Effect on Thermal Conductivity of Magnetic Multilayers, Cu/Co/Cu/Ni(Fe)

We present the first measurement of the field dependence of thermal conductivity in Cu/Co/Cu/Ni(Fe) multilayer film which shows large magnetoresistance of 50% at low temperatures. We found a large field dependence of similar magnitude in thermal conductivity with hysteresis, which suggests that the conduction electron scattering responsible for the giant magnetoresistance is mostly large angle and elastic in nature, at least at low temperatures.

Thermal conductivity measurements using a short transient hot-strip method

The transient hot-strip (THS) method has been modified to measure thermal conductivity of small test specimens. The conventional metal strip used simultaneously as the heater and the temperature sensor was substituted with a 50-Ω commercial temperature sensor (grid 5.85 mm×6.35 mm). The short transient hot-strip (STHS) method was tested on Pyrex 7740, stainless steel (NIST 1462 standard reference material), and aluminum to cover more than two orders of magnitude in thermal conductivity. The STHS method agreed with conventional measurement techniques within 3% in the thermal conductivity range 1–200 W m−1 K−1.

FIRMNESS AND THERMAL CONDUCTIVITY OF RED BEETS IN STORAGE

ABSTRACTFirmness and thermal conductivity of “Detroit Dark Red, Ferry's Strain” and “Ruby Queen” beets were determined after storage at: 0°C, 95% relative humidity (RH); 12.8°C, 24% RH, and 1.7°C, uncontrolled humidity. Firmness at fixed temperature and humidity conditions decreased with storage; it could be described by a first order rate equation. At a fixed temperature (1.7°C) and uncontrolled humidity, magnitudes of firmness varied as the humidity varied; in contrast, thermal conductivity was influenced very little. At 0°C and 95% rel. humidity, thermal conductivity remained essentially constant for four weeks. The magnitude of thermal conductivity, at room temperature and on the day of harvest, was about the same for four different varieties of beets; “King Red,”“Detroit Dark Red, Ferry's Strain,”“Ruby Queen,” and “Detroit Dark Red, Morse's Strain;” it ranged between 0.579 and 0.600 W/m °K.

Conditions for a Once-Molten Earth to Cool

Thermal history calculations have been made on a once-molten earth model: the earth is assumed to have undergone extensive melting in its early stage and the formation of the core and mantle with a proto-crust completed 4.5×109 years ago. Necessary magnitude of thermal conductivity, including the radiative components, for such an earth to cool to the present state has been obtained in terms of the opacity value as 1-3cm-1. If the earth's mantle became to consist of large crystals after the recrystallization, such a small value of opacity may be compatible with the results of thermal and optical measurements.

Thermal Conduction in Ferroelectric Ceramics

Apparatuses were constructed and measurements were made on the thermal conductivity of insulating crystals over the temperature ranges from -200°C to 600°C. For the lower temperature range, the absolute measurement was used, while for the higher one, the comparative method was adopted. The thermal conductivities of ferroelectric PbTiO 3 and antiferroelectric PbZrO 3 showed a rather large step-wise increase, in contrast to the case of BaTiO 3 , as they passed into the paraelectric state. Discussions are given of the relation between the magnitude of thermal conductivity and the crystal structure. It is pointed out that the anharmonic potential for the smaller ions should be responsible for the scattering of phonons in these substances.