International Journal of Thermophysics最新文献

The critical properties of the binary mixture of trans-1,3,3,3-Tetrafluoropropene (HFO-1234ze(E)) + 1,1,1,2-tetrafluoroethane (HFC-134a) and ternary mixture of HFO-1234ze(E) + HFC-134a + difluoromethane (HFC-32) were measured by an apparatus with variable volume. The critical properties of refrigerants can be determined by visually observing the critical opalescence phenomenon and reappearance of the meniscus. The combined expanded measurement uncertainties of the critical temperature, critical pressure and mole fraction were estimated to be less than 57 mK, 23 kPa, and 0.015 (k = 2, 0.95 level of confidence), respectively. The saturated vapor pressures and critical properties of pure HFO-1234ze(E) and HFC-134a were measured to verify the reliability of the apparatus. Redlich–Kister equations were used to correlate the critical properties of HFO-1234ze(E) + HFC-134a and the results were in good agreement with the experimental data. Cibulka’s equations were used to correlate the critical properties of HFO-1234ze(E) + HFC-134a + HFC-32 and the critical surfaces were plotted using Cibulka’s equations.

Nanofluids, colloidal suspensions of nanoparticles in a base fluid, have garnered significant research interest over the past two decades due to their potential as efficient heat transfer fluids in heat exchangers. Particularly interesting are nanofluids with nowadays very popular ionic liquids as base fluids. Understanding the behavior of nanofluids under forced convection in these systems is crucial, yet many studies have overlooked the impact on other system components. Our study focuses on the load exerted on system components by nanofluids. Specifically, we examined how varying nanoparticle concentrations influence the force exerted by the free jet flow of nanofluids on stationary obstacles. This aspect is critical as increased nanoparticle concentration generally leads to higher fluid density, potentially increasing the load on the system parts. Our findings indicate a correlation between nanoparticle concentration and the force exerted by the nanofluid's free jet flow on stationary obstacles. As the density of the nanofluid increases with higher nanoparticle concentration, so does the force exerted, confirming that the suspension of nanoparticles elevates the burden on system components. For illustrative purposes, at a temperature of 303.15 K and a nanoparticle mass concentration of 2.5 wt% in the Al₂O₃/[C₄mim][NTf₂] nanofluid, the relative increase in the force exerted by the free nanofluid jet on the stationary obstacle was approximately 5.7%. Further research into nanofluids' broader impacts is essential. Understanding these dynamics is crucial for optimizing their applications. Continued investigation into their mechanical and thermophysical effects is recommended to ensure efficient and safe integration into future technologies.

This study aims to develop sustainable PLA composites by incorporating coconut shell biochar (BC) (at 1, 2, 5 and 10 wt. %) and evaluating their mechanical, thermal, rheological, and water absorption performance. The composites exhibited enhanced tensile strength (21 to 68 MPa), hardness (28 to 53 HV), and flexural strength (a 62.5% increase), with crystallinity increasing from 24 to 47%. Thermal analysis revealed reduced stability but a 5% increase in char residue at 500 °C. Rheological improvements included higher storage/loss moduli and a 57% rise in damping factor. Water absorption increased with biochar content due to porosity and interfacial voids, confirmed by contact angle measurements. These results demonstrate the potential of PLA/BC composites as eco-friendly materials for packaging, agricultural films, and moisture-sensitive applications, contributing to sustainable development and greener urban environments.

A high-speed shadowgraph technique was developed to measure the linear thermal expansion of metallic solids up to approximately 2400 K during pulsed-current heating in vacuum. Niobium coupon specimens (3 mm × 100 mm × 0.5 mm) were resistively heated with a direct current of over 100 A for up to 2.3 s. The system incorporates a 405 nm bandpass filter, a Type-C thermocouple welded to the specimen surface, and a high-speed CMOS camera to enable high-contrast silhouette imaging under intense thermal radiation emitted by the specimen. Specimen elongation was determined by subpixel contour extraction of silhouette images, and the specimen temperature was recorded via the welded thermocouple. The relative linear thermal expansion (ε) and average coefficients of thermal expansion (α) were determined at three temperatures, yielding a maximum ε of 1.87 × 10^–2 between 334 K and 2352 K and a corresponding α of 9.28 × 10^–6 K⁻¹ at a mean temperature of 1343 K. In all three cases, the relative deviations from literature values were less than 1.2 × 10^–7 K⁻¹, which fall within the combined standard uncertainty of up to 1.83 × 10^–7 K⁻¹ (1.97%).

New physicochemical data for 2, 2, 3, 3, 4, 4, 4-heptafluoro-1-butanol (≥ 0.998 mass fr.) and 2, 2, 3, 3, 4, 4, 4-heptafluorobutyl acetate (≥ 0.994 mass fr.) are presented. The dependences of the saturated vapor pressure of 2, 2, 3, 3, 4, 4, 4-heptafluoro-1-butanol and 2, 2, 3, 3, 4, 4, 4-heptafluorobutyl acetate on temperature were obtained. The coefficients of Antoine’s equation are calculated based on the experimental temperature–pressure dependence data. This article also presents data on the rheological properties (viscosity and apparent activation energy for the viscous flow) of the studied compounds. The dependencies of refractive index and excess volume (density) on temperature are studied. Fourier transform infrared spectroscopy spectra are also provided. The experimental data presented in this paper extend and complement the information presented in the scientific literature. These data are background information and a starting point for further research in engineering design of chemical processing equipment. In addition, the received data may support the development of property models of pure substances and systems containing them, such as phase behavior and the processes underlying it.

The pressure scanner, as a highly integrated multi-channel pressure acquisition device, plays a crucial role in the high-precision measurement process. However, since pressure scanners are extremely sensitive to ambient temperature, improper calibration may directly affect the accuracy of pressure data. Therefore, the use of accurate temperature compensation algorithms is particularly important for pressure scanners. This study proposes a novel hybrid temperature compensation algorithm that combines the advantages of the Extreme Gradient Boosting (XGBoost) model in integrated learning and the artificial lemming algorithm (ALA). The algorithm is validated using experimental data obtained from a self-built calibration system. A side-by-side comparison is made with other machine learning models such as Random Forest (RF), Support Vector Regression (SVM), and XGBoost. The results show that the ALA-XGBoost model performs well with R² of 0.99951, RMSE of 0.0226, and full-scale error of only 0.081 % FS. The results validate the feasibility and effectiveness of the integrated learning model for pressure scanners temperature compensation applications.

The slow cooling of ladle slag during copper smelting offers broad potential for recovering valuable metals. Thermal conductivity is a key parameter influencing the slag’s cooling rate. However, limited research on the thermal conductivity of copper slag constrains the development of effective cooling strategies. This study systematically investigates the effects of temperature, chemical composition, and microstructure on the thermal conductivity of the SiO₂–FeO–Al₂O₃–MgO–CaO-based copper slag using laser flash analysis. As the slag cooled from 1523 K to 1398 K, 723 K, and 323 K, the corresponding thermal conductivities were 0.3594, 0.8046, 0.7085, and 0.9388 W/(m·K), respectively. Increasing SiO₂ (from 31.44 wt.% to 45 wt.%) and Al₂O₃ (from 4.24 wt.% to 12 wt.%) promoted melt polymerization, enhancing thermal conductivity at 1523 K by 27–63% and 4–26 %, respectively. By contrast, increasing the Fe/SiO2 ratio (from 1.25 to 1.6) and CaO content (from 2.88 wt.% to 11 wt.%) induced depolymerization, decreasing thermal conductivity by 7–34% and 4–10%, respectively. Increasing MgO content (from 3.1 wt.% to 11 wt.%) elevated the melting point, improving thermal conductivity by 1–37 %. The impact of the crystallization of copper slag by increasing the content of SiO₂, Al₂O₃, MgO, and CaO resulted in a decrease in thermal conductivity of solid slag by 4–31 %, whereas FeO allowed an increase in thermal conductivity by 12–88 %. These findings provide a theoretical basis for optimizing the cooling process of copper slag in industrial applications.

This study is devoted to extending our insights into peculiarities of the heat conduction of supercritical (SC) fluids in the course of rapid (due to the high heat generation power in the wire probe) transition of compressed fluid to the SC state along the isobar. The comparison is performed with respect to the thermal picture known from quasi-static experiments, where molecular thermal conductivity is usually masked by convection. The task was to construct a physical model explaining the experimental feature discovered in short-term experiments, namely, the threshold increases in the thermal resistance of the fluid boundary layer when crossing the vicinity of the critical/pseudocritical temperature. Its novelty is based on covering the range of significant deviations of the SC-parameters, namely, pressure (in statics, up to 6 p/p_c) and temperature (in pulse, up to 1.4 T/T_c), from the corresponding critical values (p_c, T_c). The model is verified by comparing its results with the data of a pulse experiment using two essentially different trajectories of penetration into the region of SC-temperatures. The developed model draws attention to potential hazards accompanying heat transfer to SC-fluids in processes with powerful heat generation, typical of a number of modern devices.

The GeSb₂Te₄–Sb₂Te₃–Te system was investigated in the temperature range of 300–450 K using X-ray diffraction (XRD) and electromotive force (EMF) measurements on reversible galvanic cells of the type: (−) GeTe (solid) │ glycerol + KCl (electrolyte) │ Ge–Sb–Te (solid) (+). The results indicate that, within the studied temperature range, elemental tellurium establishes tie lines with all telluride phases present in the system. Based on the EMF measurement data, linear equations describing the temperature dependence of the electromotive force for electrode alloys corresponding to different phase regions of the system were established. These equations were used to calculate the partial thermodynamic functions of GeTe in the alloys. By combining the obtained data with the integral thermodynamic functions of GeTe, the partial molar functions of germanium in the alloys were calculated. Based on these data and the solid-phase equilibrium diagram of the GeSb₂Te₄–Sb₂Te₃–Te system, as well as corresponding thermodynamic functions of Sb₂Te₃, the standard Gibbs free energy of formation, enthalpy of formation, and standard entropy of GeSb₂Te₄, GeSb₄Te₇, GeSb₆Te₁₀, and Sb₂Te₃-based solid solutions were calculated.