International Journal of Thermophysics最新文献

The present study provides experimental data for the liquid viscosity and surface tension of cyclohexane at or close to saturation conditions by surface light scattering between (280 and 473) K. By applying the hydrodynamic theory for surface fluctuations at the vapor–liquid phase boundary, which could be verified experimentally, the liquid viscosity and surface tension were determined simultaneously at macroscopic thermodynamic equilibrium with average relative expanded (k = 2) uncertainties of U_r(η′) = 0.020 and U_r(σ) = 0.012. For both properties, the present measurement results agree well with reference values in the literature which are restricted to a maximum temperature of 393 K for viscosity and 337 K for surface tension. The experimental results from this work contribute to an improved database for the viscosity and surface tension of cyclohexane over a wide temperature range from a temperature close to the melting point up to 473 K.

The binary vapor–liquid equilibria (VLE) of (methyl benzoate + benzyl alcohol) and (methyl benzoate + benzaldehyde) were measured and correlated using activity coefficient models. The measurements were performed using a modified Othmer still at constant pressures of 101.3, 51.3, and 21.3 kPa. The measured data were tested for consistency and correlated using the non-random two-liquid (NRTL), Wilson, and universal quasi-chemical (UNIQUAC) models. The data were also compared with predictive models, such as UNIFAC and the machine learning version of COSMO-SAC. Temperature dependence of the interaction parameters was required to accurately represent the data, covering the pressure range of the experiments. These results can be used to design a purification process for methyl benzoate production.

In supercritical carbon dioxide (S-CO₂) serpentine microtube heat exchangers, heat transfer deterioration often occurs at the bend of serpentine microtube, which reduces the efficiency and shortens the lifetime of the tube. To solve this problem, RNG k-ε turbulence model is used to simulate the flow and heat transfer of S-CO₂ when bionic fins are added. The results show that adding fins can significantly improve heat transfer, especially at low mass flux. By increasing the length of the long axis and short axis of the fins, the heat transfer efficiency is significantly improved, but the flow resistance is also increased. When the long axis and short axis are increased in the same proportion, the effect of increasing the short axis on the heat transfer performance is more obvious. This study provides a new way to strengthen the design of S-CO₂ serpentine microtube heat exchangers, which has great potential for practical application.

This study provides new experimental data for the density and viscosity of mixtures containing methyl caprate and 1-alkanol (1-propanol to 1-hexanol) at 0.1 MPa and different temperatures (293.15 K to 323.15 K). We analyzed the molecular interactions between the components and found that are weak. The PC-SAFT equation of state accurately modeled the density of the mixtures without fitted parameters. This equation of state considered hydrogen bonding between methyl caprate and 1-alkanol. Moreover, two correlations for viscosity were successfully applied to fit the experimental viscosity data with good accuracy.

Speed of sound data, measured using a dual-path pulse-echo instrument, are reported for three binary mixtures of 1,1-difluoroethylene (R-1132a) with propane at temperatures ranging from 230 to 345 K and pressures ranging from slightly above the bubble curve to a maximum pressure of 50 MPa. Significant attenuation of the pulse-echo signals was observed for measurements on pure R-1132a. Therefore, the R-1132a sample was doped with propane at mole fractions ranging from 0.0274 to 0.0887 and the propane + R-1132a mixture data was used to derive sound speeds for pure R-1132a. The data were compared to a preliminary equation of state for R-1132a, and deviations ranged from 2 % to 8 %. This demonstrates that the preliminary R-1132a EoS needs to be refit to better represent the speed of sound.

In this study, we performed a combined density functional theory (DFT) and experimental investigation of the hydrogen bonding strength and thermodynamic properties in mixtures of o-toluidine and 1-alkanol (1-propanol to 1-hexanol). The DFT calculations were carried out using the M05-2X/6–311 +  + G ∗  ∗ computational level to optimize the structures and calculate the hydrogen bonding energies. The experimental measurements were conducted using density and viscosity measurements to determine excess and deviation properties, and unraveling the strength of molecular interactions in the mixtures. The results showed that the hydrogen bonding strength and thermodynamic behavior of the mixtures were strongly influenced by the length of the alkyl chain in the 1-alkanol molecule. The DFT calculations revealed that the hydrogen bonding energies decreased with increasing alkyl chain length, while the experimental measurements showed that the excess molar volumes are increased and deviation in the viscosity are decreased. Overall, this study provides valuable insights into the interplay between hydrogen bonding and thermodynamics in o-toluidine and 1-alkanol mixtures and highlights the importance of combining DFT calculations and experimental measurements to understand complex intermolecular interactions.

We present a new wide-ranging correlation for the viscosity of nitrogen based on critically evaluated experimental data as well as ab-initio calculations. The correlation is designed to be used with densities from an existing equation of state, which is valid from the triple point to 1000 K, at pressures up to 2200 MPa. The estimated uncertainty (at the 95% confidence level) for the viscosity varies depending on the temperature and pressure, from a low of 0.2% in the dilute-gas range near room temperature, to 4% for the liquid phase at pressures from saturation up to 34 MPa, and maximum of 8% in the supercritical region at pressures above 650 MPa. Extensive comparisons with experimental data are provided.

This manuscript presents new experimental data (density and viscosity) for the binary mixtures of ethyl myristate with different secondary alcohols (2-propanol, 2-butanol, 2-pentanol, and 2-hexanol). Experimental measurements were conducted at various temperatures (293.15 K to 323.15 K), atmospheric pressure (0.1 MPa), covering a wide range of compositions for the binary mixtures. Using the experimental density and viscosity values, the molar volume excess and deviation in viscosity were obtained and the molecular interaction forces were studied as weak or strong. PC-SAFT successfully modeled the density of the mixtures without requiring any fitted parameters for the mixture. In this modeling, hydrogen bond interactions between ethyl myristate and 2-alkanol were considered. Finally, the experimental viscosity data were successfully modeled with a non-linear Belda model.

In this study, the microstructure, hardness, density, viscosity, and surface tension of molten pure Ti with TiC particles were studied via electrostatic levitation experiments, where the electrostatic levitation experiment involved container-less processing, which can suppress heterogeneous nucleation via crucibles. Microstructural observation revealed long needle-shaped α-grains across the whole area in the pure Ti sample. On the other hand, smaller needle-shaped α-grains were found in the samples with TiC particles. However, the detailed microstructural analysis of Ti + 0.7vo l%TiC sample revealed that the fine α-grains observed in the Ti + 0.7vo l%TiC are transformed from single grain of prior β phase. This is because the TiC particles dissolve into the molten Ti during the electrostatic levitation experiment. Instead, Ti–rich TiC precipitates formed by cooling can act as pinning sites rather than heterogeneous nucleation sites, which results in a finer microstructure for the samples with TiC particles during the electrostatic levitation experiment. The density of the samples is linearly related to the temperature, and it decreases with increasing temperature. In addition, a higher density is observed for the samples with TiC particles. Although linear relationships between the surface tension and temperature were found, the addition of TiC particles had no notable effect on the viscosity of the molten pure Ti.

The quest for effective thermal management solutions for microelectronic devices, catering to the escalating heat flows, necessitates innovative strategies. The significance of thermal interface materials, especially thermal greases, in minimizing thermal resistance within the "microelectronic device—heat-dissipating element" interface, has been widely acknowledged across industries such as microelectronics, aviation, and space engineering. Despite the promising reported values, a crucial consideration entails the method of ascertaining effective thermal conductivity, necessitating measurements in bulk samples to ensure accurate representations. Graphite, owing to its commercial accessibility and commendable thermal conductivity, emerges as a standout candidate for composite material development, as demonstrated in recent research. We observed that the use of graphite-based fillers, particularly in the form of well-crystallized graphite particles, effectively reduced processor temperatures and enhanced effective thermal conductivity, outperforming industrially utilized thermal greases. Our findings accentuate the potential of these materials in contributing to the development of cutting-edge composite materials for microelectronics, highlighting their high prospects for future applications in high-performance devices.