International Journal of Thermophysics最新文献

Experimental densities and sound speeds at temperatures (293.15, 303.15, 313.15, and 323.15) K and under atmospheric pressure are reported for glycerol + aniline, glycerol + pyridine, and glycerol + piperidine mixtures covering the entire composition ranges. Excess molar volumes and excess isentropic compressibilities were derived from experimental data and correlated using Redlich–Kister polynomial to test the quality of experimental data. Excess properties could be interpreted by considering the differences in molecular structure and hydrogen bonding capacity of the amines. This study utilized the Jouyban–Acree (J–A) model to capture both the compositional and temperature dependencies of mixture properties (density, sound speed, and their related properties, isobaric thermal expansivity, and isentropic compressibility). The average absolute percentage deviation of the correlated values from the experimental ones was better than 0.05 %, 0.011 %, 0.025 %, and 0.023 % for density, sound speed, isobaric thermal expansivity, and isentropic compressibility, respectively, attesting to the robustness of the J–A model to predict mixing behavior under varying conditions. The Perturbed Chain Statistical Associating Fluid Theory Equation of State (PC-SAFT EoS) was used to model the densities of the mixtures using a predictive approach. Schaaff's Collision Factor Theory (SCFT) and Nomoto's Relation (NR) were compared for their ability to model the speed of sound for the binary mixtures. The modeled densities showed good agreement with experimental data. NR outperformed SCFT in modeling speed of sound of current mixtures. The previous models (SCFT and NR) were coupled with PC-SAFT, because they require the input of liquid density data.

This paper considers the necessary conditions for using a derivative of a transient hot-wire (termed a needle probe) approach to measure the thermal conductivity of electrically conducting fluids at high temperatures, especially molten halide salts. The focus is on the development of a new theory based on a multi-layer system necessary to ensure electrical isolation of electrical wires from the surrounding fluid. This includes the use of a thin annulus of fluid to minimize convective heat transfer modes within the fluid of interest, which was inspired by the concentric cylinder method. Good measurements require the following considerations: concentricity of the probe and surrounding crucible to ensure a consistent fluid gap, accounting for corrections for deviation of the model at early times, and modeling radiation heat transfer through transparent fluids. Uncertainties are larger than transient hot-wire methods because of the deviations from experimental conditions that can easily match an analytical approximation. An appropriate estimation of the measurement uncertainty can be obtained through careful design of the instrumentation, thorough uncertainty analysis, and limiting the measurements to only the applicable thermal property ranges of the approach. The 1D model used to interpret measured temperature data has been shown to be reliable for thermal conductivity measurements ranging from at least 0.39 W (mK⁻¹) to 0.92 W (mK⁻¹) and for temperatures from 293 K to 1023 K. The approach is used to present thermal conductivity data of the molten salts NaCl–KCl (51–49 mol%) and LiCl–NaCl (72–28 mol%).

One concept for the safe storage and transport of molecular hydrogen (H₂) is the use of hydrogen carrier systems which can bind and release hydrogen in repeating cycles. In this context, the liquid system based on isopropanol and its dehydrogenated counterpart acetone is particularly interesting for applications in direct isopropanol fuel cells that are operated with an excess of water. For a comprehensive characterization of diluted aqueous solutions of isopropanol or acetone with technically relevant solute amount fractions between 0.02 and 0.08, their liquid density, liquid viscosity, and interfacial tension were investigated using various light scattering and conventional techniques as well as equilibrium molecular dynamics (EMD) simulations between (283 and 403) K. Polarization-difference Raman spectroscopy (PDRS) was used to monitor the liquid-phase composition during surface light scattering (SLS) experiments on viscosity and interfacial tension. For comparison purposes and to expand the database, capillary viscometry and dynamic light scattering (DLS) from bulk fluids with dispersed particles were also applied to determine the viscosity while the pendant-drop (PD) method allowed access to the interfacial tension. By adding isopropanol or acetone to water, density and, in particular, interfacial tension decrease significantly, while viscosity shows a pronounced increase. The behavior of viscosity and interfacial tension is closely related to the strong hydrogen bonding between the unlike mixture components and the pronounced enrichment of both solutes at the vapor–liquid interface, as revealed by EMD simulations. For an aqueous solution with an isopropanol amount fraction of 0.04, minor variations in interfacial tension and viscosity were found in the presence of pressurized H₂ up to 7.5 MPa. Overall, the results from this study contribute to an extended database for diluted aqueous solutions of isopropanol or acetone, especially at temperatures above 323 K.

Nickel-titanium (NiTi)-based shape-memory alloys (SMAs) have various applications in biomedicine, actuators, aerospace technologies, and elastocaloric devices, due to their shape-memory and super-elastic effects. These effects are induced in SMAs by a reversible martensitic phase transformation. This transformation can be achieved by applying stress or temperature differences. It is extremely difficult to measure the temperature of NiTi elements with contact thermometers because they disturb the phase transformation phenomenon. An alternative approach is contactless infrared thermography for which accurate emissivity data are mandatory. To determine the temperature distribution in NiTi components with an infrared camera, a newly constructed apparatus is presented to measure the emissivity of metals. For this purpose, a state-of-the-art infrared camera was employed to analyze the emissivity behavior with temperature, especially during the phase transformation. The emissivity of the NiTi samples was systematically studied by comparing them with a reference-quality black body cavity (BBC) having an emissivity better than 0.995. Calibration measurements revealed that the maximum deviation of the BBC temperature measured with the infrared camera was only 0.15% (0.45 K) from its temperature measured with the built-in contact thermometers. The apparatus was validated by measuring the emissivity of a polished aluminum sample and found to be in good agreement with literature data, particularly for temperatures above 340 K. Finally, the emissivity of two rough and one polished NiTi samples was measured covering the temperature range from 313 K to 423 K with an expanded uncertainty of about 0.02 ((k=2)). The studied NiTi samples have an atomic percent composition of (hbox {Ni}_{42.5}) (hbox {Ti}_{49.9}) (hbox {Cu}_{7.5}) (hbox {Cr}_{0.1}). We observed that the emissivity of NiTi varies between 0.17 and 0.31 depending on temperature. As the temperature rises, the emissivity increases rapidly during the phase transformation, and it decreases gradually beyond the austenite finish temperature. In addition, the emissivity of NiTi depends on the microstructure of the martensite and austenite phases and the surface roughness of the samples.

In addition to solar radiation, numerous factors significantly influence the temperature distribution and radiation characteristics of ground targets, thereby affecting their detectability by infrared target recognition systems. Therefore, analyzing the impact of various factors on the radiation characteristics of typical ground targets is crucial. In this study, we addressed limitations in most commercial software, which either lack detailed temperature calculations or inadequately handle radiation transfer across different spectral bands and solar radiation—factors crucial for vehicle infrared radiation characteristics. We constructed an atmospheric model and selected a vehicle as the analysis target to establish a scene model of a vehicle with the grassy background. Subsequently, we calculated the temperature distribution and infrared radiative temperature distribution of the vehicle. Following this, experiments were conducted under the corresponding conditions. The comparison between the experimental results and the simulation results revealed minimal discrepancies, demonstrating the high credibility of the simulation. The analysis reveals that air velocity significantly influences vehicle temperature, contributing to distinct temperature differentials between the front and rear sides of the vehicle. In terms of external radiation effects, solar radiation significantly influences the radiation characteristics of vehicles by inducing temperature increases, particularly influencing the vehicle’s mid-infrared reflective radiation. On the other hand, environmental and atmospheric radiation influence the vehicle’s temperature and radiative temperature to a certain extent, particularly through reflective radiation when the vehicle’s reflectance is high. This study aims to provide valuable insights for designing effective infrared camouflage patterns for ground targets.

Passive radiative cooling (PRC) offers significant potential to reduce energy consumption and carbon emissions associated with cooling. Among various approaches, paint-like systems present several advantages in terms of cost effectiveness, scalability, and ease of application. In this study, we report on a PRC system composed of a paint mixture modified with (50,%) glass bubbles (GB) and a commercial polypropylene–polyethylene–polypropylene (PP–PE–PP) film, commonly used as a battery separator. The resulting material exhibits a solar reflectance of (94,%) and a broad emittance of over (95,%) in the sky-transparent window (STW) from 8 (mu)m to 13 (mu)m. The addition of glass bubbles enhances the solar reflectance of the base paint in the near-infrared wavelengths, while the nanoporous PP–PE–PP film (NPF) topcoat improves reflectance in the UV range, remains largely transparent in the IR, and renders the overall coating washable. The material was tested under realistic outdoor conditions, comparing the performance when the PP–PE–PP film was directly applied onto the wet paint layer versus when it was used as a separate windshield enclosing the sample test chamber. Despite its high solar reflectance, no radiative cooling was observed relative to ambient temperature during peak hours (solar irradiation > 600 W·m²). However, below this threshold, a temperature drop of ({-,3},^circ)C and a cooling power exceeding 100 W·m² were observed. Notably, even when a visibly opaque convection shield was used, the configuration in which the PP–PE–PP film sealed the sample slot resulted in significant overheating of the air pocket surrounding the sample during the day. This outcome suggests that experimental setups incorporating a windshield, commonly found in the literature, may introduce an artificial overheating effect, leading to biased measurements of passive radiative cooling

Au@C core–shell nanostructures (Au@C-NS) were synthesized through a low-temperature seed-assisted hydrothermal approach using glucose as carbon source. The material characterization and chemical analysis confirm that the synthesis method allows to obtain uniform core–shell nanostructures constituted by a crystalline metal core and an amorphous carbon shell. Depending on the synthesis conditions, their average size ranges from 146 nm to 342 nm with relative standard deviation as low as 7 %. It is proposed that the characteristic monodispersity results due to a high nucleation rate of the carbon phase at the liquid–solid interface. The obtained monodisperse Au@C-NS were used to prepare water-based nanofluids with superior heat transport properties. The thermal lens analysis shows that the thermal diffusivity of Au@C nanofluids is 9.5 % and 31.3 % higher than their Au nanofluids counterparts and pure water, respectively, at particle concentration of 285 × 10¹¹ ml⁻¹. Phonon-related interactions at the metal cores and carbon shells interfaces are proposed as the heat transport mechanism behind the thermal diffusivity enhancement of the Au@C water-based nanofluids.

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.