International Journal of Thermophysics最新文献

The pulsed laser viscometer (PLV) measures viscosity and surface tension using nanoscale liquid surface deformation generated by two-beam interference of a pulsed heating laser and detects damping oscillation from the first-order diffracted intensity of a probing laser. PLV features (1) non-contact and in situ measurement, (2) high spatial resolution of 10 to 100 μm, (3) high time resolution of microseconds to milliseconds, (4) small sample volume of microliters to milliliters, and (5) a wide viscosity range of 0.1 to 10⁴ mPa·s. We established the PLV theory by solving the Navier‒Stokes‒Thermoelastic equation for volumetric heating of a liquid by a weakly absorbed pulsed laser. A new PLV experimental apparatus was developed using a pulsed YAG laser with a wavelength of 1064 nm as the heating laser, and experiments used six liquid samples (acetone, toluene, water, ethanol, 2-propanol, and 1-hexanol) at room temperature to verify that the instrument operates according to the theory. Measured viscosities agree with the literature values with an average deviation of 3.2 %. Measured surface tension agrees with the literature values with an average deviation of 6.2 %. Uncertainties are estimated at 2 % for viscosity and 3 % for surface tension. The temperature rise of the sample during the experiment was less than 0.01 K. Furthermore, the technique was found to be sensitive only to viscosity and surface tension, and insensitive to the values ​​of other thermophysical properties required for processing the data.

Density, refractive index, viscosity, surface tension, and speed of sound were experimentally determined and analyzed for [C₂mim][MeSO₄], [C₂mim][EtSO₄], [C₂eim][EtSO₄], [C₄mpy][BF₄] and [C_npy][BF₄] (n = 3, 4, 6) at atmospheric pressure and temperatures ranging from 293.15 K to 343.15 K. Expectedly, temperature exhibited the greatest impact on viscosity, as all properties decrease as temperatures increase. Linear temperature-dependent correlations were utilized for density, surface tension, refractive index, and speed of sound, while the Vogel–Fulcher–Tammann (VFT) model was applied to describe the temperature dependence of viscosity. The Laplace-Newton equation was used to calculate isentropic compressibility, and thermal expansion was calculated using the experimental density data. Furthermore, the study examined the impact of anion type and alkyl chain length on the thermophysical properties of the ionic liquids. The results reveal that the physical properties of the ionic liquids are significantly influenced by the anion type, whereas the alkyl chain length has a less significant impact. Density, speed of sound, and surface tension decrease as the length of the alkyl chain increases, while viscosity and refractive index exhibit opposing trends. Additionally, the experimental data obtained in this study is compared to theoretical models for density, surface tension, and speed of sound.

Heat flow in heterogeneous materials is of interest to engineers and scientists in a range of applications. In this paper a simplified conduction shape factor which may be used for a range of particle geometries is proposed. The shape factor may be employed using a modification of Maxwell’s effective conductivity model. Numerical simulations were performed for ellipses and ellipsoids that demonstrated that the shape factor is effective for both individual and multiple ellipses or ellipsoids up to volume fractions of 0.32, with differences between the simulated and predicted effective thermal conductivities being of the order of 1 %.

Highly oriented carbon fiber/epoxy resin (HO–CE) composites exhibit three-dimensional anisotropic heat transfer behavior, posing significant challenges for comprehensive thermophysical property characterization of the composite and its constituents. To address this challenge, a thermal property testing system for fibers and films was developed based on the T-type probe method, the 2ω method, and the laser-spot-periodic-heating (LPH) method. The system was validated using a platinum wire and an isotropic SUS304 stainless steel film as reference materials, yielding a relative measurement uncertainty below 7.8 % for thermophysical characterization. An HO–CE composite was fabricated using pitch-based carbon fibers and epoxy resin films. According to the measured thermal properties of the components, the thermal conductivity of the composite was successfully characterized using a sub-region fitting approach. The results reveal that the thermal conductivity along the fiber direction is approximately 300 times higher than that in the transverse direction. Overall, this work provides a comprehensive and reliable experimental foundation for investigating thermal transport behavior in anisotropic composite materials.

This study focuses on Thailand’s first power tunnel freezing repair project in Bangkok. Thermal property parameters of the soil strata needed for analyzing the safety of the frozen curtain were lacking. To address this, the study employed, for the first time, the TPS and TLS methods to investigate the evolution of thermal conductivity in local ground layers (including CH, CL and SM) across unfrozen, phase change, and frozen zones. A comparative analysis of the applicability of the two methods was also conducted. Experimental results indicate that thermal conductivity of the same soil is highly temperature-dependent, increasing by approximately 50 % in the frozen zone and 30 % in the phase change zone compared to the unfrozen zone. Sandy soils exhibit better thermal conductivity than clay due to the higher content of thermally conductive minerals. The Hot Disk, with its rapid response capability, is more suitable for capturing thermal conductivity variations in the phase change zone, while the KD2 Pro excels in steady-state measurements and is better suited for soils with limited moisture migration. Recommended values for the thermal conductivity of typical Bangkok soils are proposed. Additionally, a field-scale coupled hydrothermal model was developed, and the results from three different thermal conductivity models—measured, fixed, and geometric mean—were compared. The comparison demonstrated that the measured thermal conductivity model more accurately simulates variations in the temperature field. This research provides key thermal parameters for simulating temperature fields in tropical artificial ground freezing projects and offers a scientific basis for the optimized design of frozen curtains under similar geological conditions.

2,4,6-Trinitrotoluene, as a classical energetic material, exhibits dissolution behavior that permeates every critical stage—from production purification and formulation processing to environmental migration. To address the existing gap in fundamental physicochemical data for TNT in mixed-solvent systems, this study systematically measured the solubility of TNT in binary mixed solvents composed of pyridine and ethanol across a temperature range of 293.15 to 333.15 K. The experimental results indicate that the solubility of TNT increases with rising temperature and follows a regular trend with variations in solvent composition at constant temperature. To gain deeper insight into the dissolution thermodynamics and to establish predictive models, the experimental data were correlated and fitted using the modified Apelblat model, the van’t Hoff model, the Yaws model, and the CNIBS/R‑K model. All models demonstrated excellent fitting accuracy, confirming their capability to describe the phase equilibrium behavior of this system. This work not only provides comprehensive experimental phase equilibrium data for the system, but also offers model-based support for the development of TNT related processes, solvent screening, and environmental risk assessment.

In situ evaluation of thermal transmittance using infrared thermography is challenging, particularly for heavyweight concrete envelopes where surface temperature does not directly represent heat flux. A reinforced concrete building with design U-values of 0.181 W/(m²·K) for the wall and 1.268 W/(m²·K) for the window was examined to compare three non-destructive approaches: the heat flow meter method, the ISO 9869–2 infrared thermography procedure, and an exterior infrared method based on the Jürges equation. The heat flow meter technique provided the most reliable reference, with deviations of 4.9% for the wall and 4.7% for the window, but required long stabilization and interior access. The ISO-based infrared approach produced reasonable estimates for windows on both sides, whereas it failed to converge for heavyweight walls. This behavior is attributed to the high thermal mass of concrete, where transient heat storage decouples surface temperature from actual heat flux, even when heat transfer coefficients are measured directly. The exterior infrared method showed close agreement for walls under low-wind night-time conditions, while large deviations were observed for windows because radiative transmittance and frame–glass interaction cannot be represented by a single exterior surface temperature. The applicability of infrared thermography depends on component type and boundary conditions. The ISO-based procedure is more appropriate for windows, whereas the exterior method can support wall assessment under controlled environments. These findings contribute to a thermophysically consistent framework for non-destructive U-value evaluation of heavyweight and lightweight envelopes and help clarify the conditions for method application.

Graphene-based films are promising for advanced thermal management, yet achieving high thermal conductivity typically requires energy-intensive, high-temperature annealing. Herein, we report a systematic study on tuning the structural and transport properties of partially reduced graphene oxide (PRGO) films through the incorporation of polymer additives followed by moderate temperature (1000 °C) annealing. Three polymers including chitosan (CS), polyimide (PI), and polydopamine (PDA) are investigated. Structural characterization (SEM, XRD, Raman, XPS) reveals that CS reduces defect density after thermal annealing at 1000 °C. Thermal characterization indicates that all additives improve thermal diffusivity, but only CS increases film density, resulting in a net rise in thermal conductivity. For electrical conductivity, CS markedly boosts conductivity, while PI and PDA degrade it. These property trends remain consistent from 10 to 320 K. Analysis of the temperature coefficient of resistance (TCR) indicates a significantly reduced TCR for the modified film (0.01–0.02%·K⁻¹), nearing the value of pristine graphene (0.02–0.05% K⁻¹ at 260–350 K). Furthermore, low-temperature thermal reffusivity analysis confirms that the polymer additives suppress phonon-defect scattering and enlarge structural domains, with PI uniquely strengthening interatomic bonding. Our results demonstrate that CS is a particularly effective additive for concurrently enhancing both thermal and electrical performance in PRGO films, providing a viable polymer-mediated route for microstructure-engineered graphene-based materials.

Difluoromethane (R32) is a widely adopted low-global-warming-potential refrigerant and a common constituent of other important refrigerant blends. Nonetheless, low-uncertainty thermodynamic properties are scarce for this compound. This work reports experimental sound speeds of liquid and supercritical difluoromethane at temperatures from (306 to 373) K and at pressures up to 40 MPa, measured using a double-path pulse-echo apparatus with standard uncertainties between (0.02 and 0.15) %. Using the method of thermodynamic integration, these data were combined with low-uncertainty density data from the literature to derive a comprehensive set of thermodynamic properties in the liquid phase. This extends the range of data available for this crucial compound, particularly in the supercritical region. The low-uncertainty experimental sound-speed data and derived thermodynamic properties are expected to aid the development of an improved equation of state for difluoromethane.