Simultaneous measurements of thermal conductivity and thermal diffusivity of Se90?xTe5Sn5Inx (x?=?0, 3, 6, and 9) multi-component chalcogenide glasses

Measurements of thermal conductivity and thermal diffusivity of twin pellets of Se_90−x Te₅Sn₅In _x (x = 0, 3, 6, and 9) chalcogenide glasses were carried out at room temperature using transient plane source technique. The measured values of thermal conductivity and thermal diffusivity were used to determine the specific heat per unit volume of these glasses in the composition range of investigation. Results indicated that both values of thermal conductivity and thermal diffusivity were increased with addition of indium concentration at the cost of selenium, whereas the specific heat per unit volume was slightly decreases with increase of indium content. This compositional dependence behavior of the thermal conductivity and diffusivity can be explained in terms of the iono-covalent type of bonds, which In (indium) makes with Se as it is incorporated in the Se–Te–Sn glass.     

Thermal Conductivity and Thermal Diffusivity of Liquid Aromatic Hydrocarbons Undistorted by Radiation Heat Transfer

The values of thermal conductivity and thermal diffusivity are measured for seven substances (benzene, toluene, -n-m-xylenes, ethylbenzene, and isopropylbenzene) at temperatures T = 293–593 K and pressures P = P _S – 30 MPa. The obtained values of thermal conductivity and thermal diffusivity differ from the reference values by not more than 15%. The generalizing dependences are given, which describe the thermal conductivity, thermal diffusivity, and heat capacity per unit volume of n-alkanes, alkenes, and aromatic hydrocarbons.     

The Thermal Conductivity, Thermal Diffusivity, and Specific Heat of Liquid n-Pentane

The thermal conductivity and thermal diffusivity of liquid n-pentane have been measured over the temperature range from 293 to 428 K at pressures from 3.5 to 35 MPa using a transient hot-wire instrument. It was determined that the results were influenced by fluid thermal radiation, and a new expression for this effect is presented. The uncertainty of the experimental results is estimated to be better than ±0.5% for thermal conductivity and ±2% for thermal diffusivity. The results, corrected for fluid thermal radiation, are correlated as functions of temperature and density with a maximum uncertainty of ±2% for thermal conductivity and ±4% for thermal diffusivity. Derived values of the isobaric specific heat are also given.     

Thermal Transport Properties of Cd<Subscript>1-<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Se Mixed Crystals Measured by Means of the Photopyroelectric Method

The concentration dependence of the thermal conductivity and thermal diffusivity were determined for Cd_1-x Mg _x Se mixed crystals in the temperature range between 20 ^◦C and 40 ^◦C. To determine the thermal transport properties, the photopyroelectric setup in the back detection configuration was constructed. In the concentration range 0< x <0.36, both thermal conductivity and thermal diffusivity were found to decrease with increasing magnesium concentration as well as with increasing temperature. The observed concentration dependence is discussed in the framework of the Adachi model.     

Study of thermal properties of glass system 77% B2O3-23% PbO doped with ZnO in the temperature range 300 to 700 K

The thermal properties: specific heat capacity (C _p), thermal conductivity (), and thermal diffusivity (a) of the glass system 77% B₂O₃-23% PbO doped with ZnO, were measured in the temperature range 300 to 700 K. It was found that electronic conduction has no significant contribution to the thermal conductivity. The main mechanism of heat transfer is therefore due to both phonons and photons. A discussion of the results is made in view of various theoretical aspects.     

Measurement of thermal properties of iron oxide pellets

The thermal properties of iron oxide pellets of different porosity and prepared by reduction at different rates were investigated in the range of room temperature to about 800°C. The thermal diffusivity a was measured by a laser flash method and the specific heat C _p was measured by adiabatic scanning calorimetry. The thermal conductivity was calculated from the relation =aC p, where is the density of the specimen.For nonreduced iron oxide pellets, the thermal diffusivity and thermal conductivity decreased with increase in temperature and porosity. The specific heat increased with increasing temperature and there was a transformation point at which the specific heat reached a maximum. In prereduced iron oxide pellets, the thermal diffusivity and thermal conductivity were very small compared with the nonreduced pellets and they gradually increased with increasing temperature. The specific heat had a minimum and a maximum at about 300 and 600°C, respectively, and the scale of these features became smaller with increase in the reduction rate.Paper presented at the Fourth Japan Symposium on Thermophysical Properties, October 20–22, 1983, Yokohama, Japan.     

Thermal-Conductivity and Thermal-Diffusivity Measurements of Nanofluids by 3<Emphasis Type="Italic">ω</Emphasis> Method and Mechanism Analysis of Heat Transport

A 3ω technique is developed for simultaneous determination of the thermal conductivity and thermal diffusivity of nanofluids. The 3ω measuring system is established, in which a conductive wire is used as both heater and sensor. At first, the system is calibrated using water with known thermophysical properties. Then, the thermal conductivity and thermal diffusivity of TiO₂/distilled water nanofluids at different temperatures and volume fractions and the thermal conductivity of SiO₂ nanofluids with different carrier fluids (water, ethanol, and EG) are determined. The results show that the working temperature and the carrier fluid play important roles in the enhancement of thermal transport in nanofluids. These results agree with the predictions for the temperature dependence effect by the Brownian motion model and the micro-convection model. For SiO₂ nanofluids, the thermal-conductance enhancement becomes strong with a decrease in the heat capacity of the carrier fluids. Finally, according to our results and mechanism analysis, a corrected term is introduced to the Brownian motion model for providing better prediction of heat transport performance in nanofluids.     

Dielectric and thermal properties of xPbTiO3-(1 − x)SrTiO3 Polycrystals

SrTiO₃ and PbTiO₃ perovskites are combined to form the xPbTiO₃-(1 – x)SrTiO₃ (PST) solid solution. In this work, a study of its dielectric and thermal properties is reported as a function of PbTiO₃ content. The dielectric properties of the xPbTiO₃-(1 – x)SrTiO₃ solid solution are determined through a thermoelectric analysis technique and hysteresis measurements. Such measurements made at room temperature for all compositions show the influence of one component upon the other resulting in a response to the electric field that involves a strained lattice behavior. A limiting case of antiferroelectric-like behavior is observed for x = 0.5. The thermal properties such as the specific heat capacity (c) and thermal diffusivity () were determined using a photoacoustic technique (PA) and the temperature relaxation method (TRM). The thermal conductivity was calculated from the results obtained for c and .     

Composition dependence of some thermo-physical properties of multi-component Se78−x Te20Sn2Bi x (0 ≤ x ≤ 6) chalcogenide glasses

New multi-component glassy materials with composition of Se_78?x Te₂₀Sn₂Bi _x (0 ≤ x ≤ 6) have been synthesized by well-known melt quenching technique. The as-prepared glasses have been characterized by applying an advanced transient plane source technique to study their thermal transport properties (effective thermal conductivity, diffusivity, specific heat per unit volume) at room temperature. Density measurements have been done to correlate the obtained results. Using the experimental data of density measurements, the basic physical parameters, such as mean atomic volume, compactness, average coordination number etc., are evaluated for the synthesized glasses and the results are discussed as a function of glass composition. We have also determined the phonon mean free path (τ) using the experimental value of effective thermal diffusivity. The composition dependence of the thermal transport properties of aforesaid glassy system has also been discussed.     

Crystal growth and characterization of Yb-doped Gd3Ga5O12

Single crystals of (Yb_xGd_1−x)₃Ga₅O₁₂ (0.0 ≤ x ≤ 1.0) have been grown by the micro-pulling-down method. Formation of continuous solid solutions with a garnet structure was confirmed. Composition dependence of the lattice constant, thermal diffusivity, specific heat capacity and thermal conductivity was investigated. Assignment of the Yb³⁺-energy levels in Gd₃Ga₅O₁₂-host lattice has been performed by using absorption, emission and Raman spectroscopy measurements at both, room temperature and at 12 K.     

Effect of Cryogenic Treatment on Thermal Behavior of WC-9Ni-xCeO2 Cemented Carbides

A series of specimens of WC-9Ni-xCeO₂ cemented carbides were prepared. The influences of CeO₂ addition and cryogenic treatment (CT) on thermal conductivity, thermal diffusion coefficient, and heat capacity of the alloys were investigated using a Hot Disk thermal constant analyzer, a X-ray diffractometer (XRD), and a scanning electron microscope (SEM) coupled with an energy dispersive X-ray detector (EDS). The results indicated that with the increase in CeO₂ content in WC-9Ni-xCeO₂ cemented carbides, the thermal conductivity and thermal diffusion coefficient first increase and then decrease. The change in heat capacity of the cemented carbides, however, does not show obvious regularity. CT tends to increase the thermal conductivity, thermal diffusion coefficient, and decrease the heat capacity of WC-9Ni-xCeO₂ cemented carbides. Notably, the degree of influence of CT on thermal properties of the cemented carbides with various CeO₂ contents is obviously different. After CT, with an increase in the CeO₂ content, the variation of amplitude of thermal conductivity decreases. Similar situations also appear in the other two kinds of thermal properties.     

A noncontact method for measuring thermal conductivity and thermal diffusivity of anisotropic materials

A noncontact method for measuring the thermal conductivity and thermal diffusivity of anisotropic materials is proposed. This method is based on the fact that the surface temperature variation with time depends on the thermal properties of the material when its surface is heated locally. The three-dimensional transient heat conduction equation in the material is solved numerically. The dimensionless average surface temperature variations are obtained along each principal axis: that is, thex andy axes. The relation between the dimensionless temperature and the Fourier number is expressed by a polynomial equation and used as a master plot, which is a basic relation to be compared with measured temperature variation. In the experiments, the material surface is heated with a laser beam and the surface temperature profiles are measured by an infrared thermometer. The measured temperature variations with time are compared with the master plots to yield the thermal conductivity λ _x and thermal diffusivityx _v in thex direction and the thermal conductivity ratioE _xy (=λ _y λ _x ) simultaneously. To confirm the applicability and the accuracy of the present method, measurements were performed on multilayered kent-paper, vinyl chloride, and polyethylene resin film, whose thermal properties are known. From numerical simulations, it is found that the present method can measure the thermophysical properties λ _x , α _x andE _xy within errors of ±6, ±22, and ±5%, respectively, when the measuring errors of the peak heat flux, the heating radius, and the surface temperature rise are assumed to be within ±2, ±3%, and ±0.2 K, respectively. This method could be applied to the measurement of thermophysical properties of biological materials.     

Thermal diffusivity, thermal conductivity, and specific heat of flax fiber–HDPE biocomposites at processing temperatures

There is increasing work on the use of flax fibers as reinforcement for manufacturing composites because of their lower cost and environmental benefit. During manufacturing of such natural fiber–plastic composites, heat transfer is involved, but information about the thermal conductivity and thermal diffusivity at the processing temperatures is not available. In this study, the thermal conductivity, thermal diffusivity, and specific heat of flax fiber–high density polyethylene (HDPE) biocomposites were determined in the temperature range of 170–200 °C. The fiber contents in biocomposites were 10%, 20%, and 30% by mass. Using the line-source technique, the instrumental setup was developed to measure the thermal conductivity of biocomposites. It was found that the thermal conductivity, thermal diffusivity, and specific heat decreased with increasing fiber content, but thermal conductivity and thermal diffusivity did not change significantly with temperature in the range studied. The specific heat of the biocomposites increased gradually with temperature.     

Extension of the quasilinear method of determining thermophysical characteristics to the case of anisotropic materials

The article reports on the initial part of the stage of regular thermal regime of a plate heated by a constant heat flux, and a method is suggested for determining thermal conductivity and thermal diffusivity.Notation T temperature of the plate - T₀ binitial temperature of the plate and ambient temperature - g volume density of the heat sources - q heat flux density - _x thickness of the plate - _x thermal conductivity along the x axis - a _x thermal diffusivity along the x axis - heat transfer coefficient - Fo Fourier number - B Biot number - density of the material of the plate - c heat capacity - t time Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 55, No. 4, pp. 611–616, October, 1988.     

Some Thermal Properties of a Copper–Tin Alloy

The thermal properties (heat capacity, thermal diffusivity, and electrical resistivity) of a Cu + 10 wt% Sn alloy in both solid and liquid phases have been reported. Using these values it was confirmed that the Lorenz relation is suitable for obtaining thermal conductivity from electrical resistivity in the liquid phase of this alloy. Also, the temperature differential (d/dT) obtained from such an approach was in excellent agreement with the thermal conductivity values calculated from thermal diffusivity.     

Thermophysical Properties of Sn–Ag–Cu Based Pb-Free Solders

Lead–tin (Pb–Sn) alloys are the dominant solders used for electronic packaging because of their low cost and superior properties required for interconnecting electronic components. However, increasing environmental and health concerns over the toxicity of lead, combined with global legislation to limit the use of Pb in manufactured products, have led to extensive research and development studies of lead-free solders. The Sn–Ag–Cu ternary eutectic alloy is considered to be one of the promising alternatives. Except for thermal properties, much research on several properties of Sn–Ag–Cu alloy has been performed. In this study, five Sn–xAg–0.5Cu alloys with variations of Ag content x of 1.0 mass%, 2.5 mass%, 3.0 mass%, 3.5 mass%, and 4.0 mass% were prepared, and their thermal diffusivity and specific heat were measured from room temperature to 150 °C, and the thermal conductivity was calculated using the measured thermal diffusivity, specific heat, and density values. Also, the linear thermal expansion was measured from room temperature to 170 °C. The results show that Sn–3.5Ag–0.5Cu is the best candidate because it has a maximum thermal conductivity and a low thermal expansion, which are the ideal conditions to be a proper packaging alloy for effective cooling and thermostability.     

The effects of cobalt substitution on the thermal diffusivity of YBa2Cu3O7?δ superconductor

The thermal diffusivity κ(T) of the cobalt-substituted sintered YBCO system, YBa₂Cu_3−x Co _x O_7∮δ (x=0.0, 0.1), has been measured to, investigate, effects of atomic substitution and charge carrier concentration on the thermal diffusion processes. The thermal diffusivity was measured in the temperature range 35–300 K, using the transient-plane-source technique. The results show that, belowT _c , the κ(T) values of the doped (x=0.1), samples are lower than the corresponding values for the undoped (x=0.0) samples. This may be due to the difference in the free-charge carrier concentrations of the two samples. A decoupling between the conducting Cu−O planes as a result, of Co-doping in the chain sites may contribute to additional decrease in the thermal diffusivity of the doped sample. An attempt was made to explain the rise in the thermal diffusivity belowT _c by adopting a recent theoretical model based on the existence of weakly damped collective electron excitations of Bose type, with acoustic dispersion relation, (acoustic plasmons) inside the superconducting gap.     

Characterization of Sodium Nitrate as Phase Change Material

In this article the results of material investigations of sodium nitrate (NaNO₃) with a melting temperature of 306 °C as a phase change material (PCM) are presented. The thermal stability was examined by kinetic experiments and longduration oven tests. In these experiments the nitrite formation was monitored. Although some nitrite formation in the melt was detected, results show that the thermal stability of NaNO₃ is sufficient for PCM applications. Various measurements of thermophysical properties of NaNO₃ are reported. These properties include the thermal diffusivity by the laser-flash, the thermal conductivity by the transient hot wire, and the heat capacity by the differential scanning calorimeter method. The current measurements and literature values are compared. In this article comprehensive temperature-dependent thermophysical values of the density, heat capacity, thermal diffusivity, and thermal conductivity in the liquid and solid phases are reported.     

The thermal conductivity and heat capacity of gaseous argon

This paper presents new absolute measurements of the thermal conductivity and of the thermal diffusivity of gaseous argon obtained with a transient hot-wire instrument. We measured seven isotherms in the supercritical dense gas at temperatures between 157 and 324 K with pressures up to 70 MPa and densities up to 32 mol · L^–1 and five isotherms in the vapor at temperatures between 103 and 142 K with pressures up to the saturation vapor pressure. The instrument is capable of measuring the thermal conductivity with an accuracy better than 1% and thermal diffusivity with an accuracy better than 5%. Heat capacity results were determined from the simultaneously measured values of thermal conductivity and thermal diffusivity and from the density calculated from measured values of pressure and temperature from an equation of state. The heat capacities presented in this paper, with a nominal accuracy of 5%, prove that heat capacity data can be obtained successfully with the transient hot wire technique over a wide range of fluid states. The technique will be invaluable when applied to fluids which lack specific heat data or an adequate equation of state.     

Thermal Conductivity during Phase Transitions

Thermal conductivity is a very basic property that determines how fast a material conducts heat, which plays an important and sometimes a dominant role in many fields. However, because materials with phase transitions have been widely used recently, understanding and measuring temperature‐dependent thermal conductivity during phase transitions are important and sometimes even questionable. Here, the thermal transport equation is corrected by including heat absorption due to phase transitions to reveal how a phase transition affects the measured thermal conductivity. In addition to the enhanced heat capacity that is well known, it is found that thermal diffusivity can be abnormally lowered from the true value, which is also dependent on the speed of phase transitions. The extraction of the true thermal conductivity requires removing the contributions from both altered heat capacity and thermal diffusivity during phase transitions, which is well demonstrated in four selected kinds of phase transition materials (Cu₂Se, Cu₂S, Ag₂S, and Ag₂Se) in experiment. This study also explains the lowered abnormal thermal diffusivity during phase transitions in other materials and thus provides a novel strategy to engineer thermal conductivity for various applications.