International Journal of Thermophysics

A new method for deriving accurate thermodynamic properties of gases and vapors (the compression factor and heat capacities) from the speed of sound is recommended. A set of PDEs connecting speed of sound with other thermodynamic properties is solved as a nonlinear least squares problem, using a modified Levenberg–Marquardt algorithm. In supercritical domain, boundary values of compression factor are imposed along two isotherms (one slightly above Tc and another several times Tc) and two isochores (one at zero density and another slightly above ρc). In subcritical domain, the upper isochore is replaced by the saturation line, the lower isotherm is slightly above the triple point, and the upper isotherm is slightly below the critical point. Initial values of compression factor inside the domains are obtained from the boundary values by a cubic spline interpolation with respect to density. All the partial derivation with respect to density and temperature, as well as speed of sound interpolation with respect to pressure, is also conducted by a cubic spline. The method is tested with Ar, CH4 and CO2. The average absolute deviation of compression factor and heat capacities is better than 0.002 % and 0.1 %, respectively.

Using the flash technique, the thermal diffusivity of iron oxide has been measured as a function of time at temperatures ranging from 623 to 753 K to study the isothermal decomposition of wustite to magnetite and iron. The results are briefly discussed in terms of transformation kinetics and it is shown that the data are consistent with the growth of a fixed number of nuclei, all of which are present at the start of transformation.

In the past decade it has been suggested that the isotopic enrichment of 28-silicon enhances its thermal properties. Thus, 28-silicon is suitable as a heat sink in large-scale integrated circuits. Although some studies have focused on the measurement of isotopically enriched silicon's thermal properties, accurate experimental data are not sufficient because of this material's high conductivity and large heat capacity which make measurement difficult. However, the dynamic grating radiometry (DGR) method has been successfully developed to measure the thermal diffusivity of 28-silicon. In the DGR method, the sample is heated by interference of two pulsed laser beams, and the temperature decay is monitored by an infrared detector. By analyzing the temperature changes of the peaks and valleys of the thermal grating, the thermal diffusivities parallel and perpendicular to the sample surface are obtained simultaneously. In this paper, the optimum conditions of the experimental setup for measuring isotopically enriched silicon are discussed. The comparison of thermal diffusivities between 28-silicon and natural silicon (with a thickness of about 100 μm) is presented, and the applicability of DGR to isotope engineering is reported.

The density of molten silicon was measured using a newly developed pycnometer made of boron nitride. The present method has many advantages for measuring the density of molten silicon, which has a high temperature and can be easily oxidized. The pycnometer was precisely machined, and its volume at high temperatures was acculately determined. The procedure to overflow the excess melt was carried out in a closed apparatus under a helium atmosphere. A special procedure was introduced to avoid the error generated by the volume expansion of silicon when it solidified. The total uncertainty of the measurement was estimated to be within 0.5%. The measured density showed a linear relationship with respect to temperature and agreed well with literature values. The expansion coefficient of molten silicon was similar to those of typical molten metals in spite of the low expansion coefficient of solid silicon. This suggested that the structural change of molten silicon was similar to those of typical metals.

Molar heat capacities at constant volume (C v) of 1,1-difluoroethane (R152a) and 1,1,1-trifluoroethane (R143a) have been measured with an adiabatic calorimeter. Temperatures ranged from their triple points to 345 K, and pressures up to 35 MPa. Measurements were conducted on the liquid in equilibrium with its vapor and on compressed liquid samples. The samples were of high purity, verified by chemical analysis of each fluid. For the samples, calorimetric results were obtained for two-phase ((C v (2) ), saturated-liquid (C σ or C x ' ), and single-phase (C v) molar heat capacities. The C σ data were used to estimate vapor pressures for values less than 105 kPa by applying a thermodynamic relationship between the saturated liquid heat capacity and the temperature derivatives of the vapor pressure. The triple-point temperature and the enthalpy of fusion were also measured for each substance. The principal sources of uncertainty are the temperature rise measurement and the change-of-volume work adjustment. The expanded relative uncertainty (with a coverage factor k=2 and thus a two-standard deviation estimate) for C v is estimated to be 0.7%, for C v (2) it is 0.5%, and for C σ it is 0.7%.

The two-phase isochoric heat capacity of nitrogen tetroxide was measured in the temperature range from 261.74 K to the critical temperature (431.072 K) at densities between 201.21 and 1426.5 kg·m−3 using a high-temperature and high-pressure adiabatic calorimeter. The measurements were performed in the two-phase region for 26 isochores (15 liquid and 11 vapor densities) including the coexistence curve and critical region. Uncertainties of the measurements are estimated to be 2%. The original temperatures and C V data were converted to the ITS-90. The liquid and vapor two-phase isochoric heat capacities, temperatures, and densities at saturation were extracted from experimental data for each measured isochore. From measured (T S, ρ S, C′ V2, C″ V2) data, the values of second temperature derivatives of vapor-pressure d 2 P S/dT 2 and chemical potential d 2 μ/dT 2 were derived using the Yang–Yang relation. The results were compared with values calculated from other vapor-pressure equations. The values of saturated densities and critical parameters derived in calorimetric experiments were compared with literature data. The unusual temperature behavior of d 2 P S/dT 2 and d 2 μ/dT 2 was found at low temperatures around 351 K and near the critical point.

Thermal transport properties have attracted extensive research attentions over the past decades. First-principles-based approaches have proved to be very useful for predicting the thermal transport properties of materials and revealing the phonon and electron scattering or propagation mechanisms in materials and devices. In this review, we provide a concise but inclusive discussion on state-of-the-art first-principles thermal modeling methods and notable achievements by these methods over the last decade. A wide range of materials are covered in this review, including two-dimensional materials, superhard materials, metamaterials, and polymers. We also cover the very recent important findings on heat transfer mechanisms informed from first principles, including phonon–electron scattering, higher-order phonon–phonon scattering, and the effect of external electric field on thermal transport. Finally, we discuss the challenges and limitations of state-of-the-art approaches and provide an outlook toward future developments in this area.

The temperature dependence of density, normal spectral emissivity, heat capacity at constant pressure, and thermal conductivity of the V melt were measured with high accuracy using electromagnetic levitation in a static magnetic field. Surface vibration, translational motion, and convection of the electromagnetically levitated droplet sample were suppressed by the magnetic field. In the measurement of thermal conductivity, convection in the V-melt was sufficiently suppressed by the application of a field of 7 T or higher. In this study, the measured emissivity and thermal conductivity are compared with those evaluated using the free-electron models (Drude model and Wiedemann–Franz rule). Correlations between the density of states and thermal diffusivity at the Fermi energy of transition metals in the liquid state are investigated and the applicability of Mott's s–d scattering model is discussed.