Journal of Thermal Analysis and Calorimetry最新文献

A sustainable energy system is the backbone of reducing carbon emissions, and utilizing supercritical carbon dioxide’s superior thermophysical properties for heat transfer in microchannels is a promising approach. Although research on supercritical carbon dioxide (SCO₂) heat transfer in microchannels is growing, comprehensive reviews are still limited. Existing studies mainly focus on individual experiments or simulations, with inconsistent findings and no unified theory or optimization strategy. To address these gaps, a systematic summary of SCO₂ heat transfer in microchannels is provided, with a focus on key performance factors, degradation mechanisms, and optimization strategies. Accordingly, a comprehensive summary and analysis of SCO₂ heat transfer in microchannels is presented. Recent literature on SCO₂ heat transfer was systematically reviewed, encompassing experimental studies, degradation phenomena, influencing factors, and evaluations of existing research methods. Optimization strategies for heat transfer efficiency are outlined, and key challenges in SCO₂ heat transfer in microchannels are identified, including complex mechanisms, inconsistent findings, and the absence of a standardized evaluation framework. Directions for future research include refining models of heat transfer mechanisms, exploring strategies to mitigate heat transfer degradation, and improving the molecular dynamics simulation and balancing it with high-precision experiment. This study not only provides a comprehensive understanding of the current SCO₂ heat transfer field for the academic community but also provides constructive suggestions and guidance for the further development of the technology.

The present study aims at the synthesis of Schiff base-containing platinum(II) complexes with a general formula of [Pt(ketone)₂A(L₂)], where ketones are 2-heptanone, 2-octanone or 3-octanone; A is hydrazine, phenylhydrazine or o-phenylene-diamine; L is 1-naphthylamine, 2-amino-pyrimidine, 2-methylimidazole or 2-amino-4-methylpyridine. The complexes were obtained from reactions between PtCl₂, ketones and amine compounds in appropriate solvents. A detailed analysis of the physicochemical properties of the complexes was accomplished using: Fourier-transform infrared (FTIR) spectroscopy, thermal analysis (TA), mass spectrometry (MS), nuclear magnetic resonance (NMR), UV–Vis spectroscopy, powder X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) spectroscopy. The biological effects of some selected complexes on the Gram-positive bacteria strain Staphylococcus aureus and on normal and tumor cells were also investigated. Two complexes (C3 and C9) showed antibacterial activity, the inhibitory effect being dependent on the concentrations applied. Two compounds (C2 and C9) exhibited antitumoral activity against two ovarian cancer cell lines, through increased cytotoxicity cellular death (mostly by late apoptosis) and DNA damage. The compound C2 affected also platinum-resistant tumor cells. These effects were milder on normal cells, suggesting a possible protective effect on healthy tissues. The results highlight the potential utility of this class of compounds in medicinal chemistry and the importance of testing them in further studies to ascertain their application as future antibacterial and/or anticancer drugs.

This study explores the use of poly(allyl methacrylate) (polyAMA) for the microencapsulation of n-alkane phase change materials (PCMs), focusing on its effectiveness as a shell material and its impact on thermal performance. PolyAMA provides both efficient encapsulation and enhanced thermal stability for hexadecane and pentadecane, which were encapsulated via emulsion polymerization. Morphological analysis showed that the microcapsules had uniform, spherical shapes with median diameters of 33 μm for hexadecane (microHD) and 43 μm for pentadecane (microPD). Differential scanning calorimetry (DSC) revealed high latent heat storage capacities of 103.63 J g⁻¹ for microHD, and 113.38 J g⁻¹ for microPD, confirming their suitability for thermal energy storage with good thermal stability, with initial degradation temperatures above 120 °C. To evaluate practical applicability, microPD was incorporated into fiberglass, which is a widely used and thermally stable material in construction, forming composite structures with improved thermal regulation. The results demonstrate that polyAMA-based n-alkane microcapsules possess exceptional thermal properties, making them ideal candidates for TES in buildings and textiles. By effectively mitigating rapid temperature fluctuations, these materials can contribute to more comfortable and energy-efficient indoor environments, ultimately promoting sustainable building and textile applications.

This study explores the free convection flow and heat transfer of a fluid containing nano-encapsulated phase change nanoparticles (NEPCM) in a square cavity with three different cases of hot and cold walls. The core–shell particles integrate a phase-change material (PCM) can absorb and release latent heat during solid–liquid transitions. The horizontal walls of the cavity are thermally insulated, while the vertical walls are subjected to differential temperature conditions, inducing natural fluid circulation. To assess the thermal efficiency of the system, several configurations of thermal boundary conditions were compared. The governing equations for conservation of mass, momentum and energy were formulated in dimensionless form and solved numerically using the finite element method. The results are presented to show the impact of various parameters which ranged as Rayleigh number (10³ ≤ Ra ≤ 10⁶), fusion temperature (0.2 ≤ θ_f ≤ 0.6), Stefan number (0.2 ≤ Ste ≤ 0.8), volume fraction of NEPCM particle (0 ≤ ϕ ≤ 0.05). Numerical validation was carried out to ensure the accuracy of the results. The results show that the dimensionless melting temperature (θ_f) is a key parameter in heat transfer enhancement, it was found also that NEPCM particles significantly enhance natural convection heat exchange. On the other hand, the best performance is achieved when the hot and cold walls are vertically aligned. At Ra = 10⁶, adding 5% NEPCM increases the average Nusselt number by 11.5%. This study highlights the potential of NEPCMs to enhance thermal performance in natural convection systems and energy storage capacity.

This study investigates the heat collection efficiency of flat-plate solar collectors using water-based Fe₃O₄ and Cu nanofluids. The effects of nanofluid mass fraction, particle size, flow rate, and external magnetic field on heat collection efficiency were experimentally analyzed. The results show that within a certain concentration range, the heat collection efficiency of the nanofluids gradually increases with increasing mass fraction and flow rate. However, when the mass fraction reaches 0.5 mass%, the efficiency slightly decreases due to the agglomeration of nanoparticles at high concentrations, which affects stability. Smaller particle sizes lead to higher heat collection efficiency. Compared to conventional heat transfer fluids, the maximum heat collection efficiencies of Fe₃O₄ and Cu nanofluids increased by 12.73% and 17.5%, respectively. Under an external magnetic field, the heat collection efficiency significantly improved. At a magnetic field strength of 100 Gs, the Fe₃O₄ nanofluid exhibited a 9.63% increase in efficiency compared to the non-magnetic field condition.

This study explores the structural and thermal behavior of different smectites intercalated with the cationic surfactant ethyl lauroyl arginate (LAE®) at loadings up to 1.0 of the smectites' cation exchange capacity (CEC). X-ray diffraction (XRD) confirmed systematic expansion of the basal spacing (d₀₀₁), reaching up to 2.29 nm, with changes governed by surfactant content, exchangeable cation type, and layer charge. LAE® was incorporated exclusively via ion exchange, as evidenced by exchangeable cation release, although steric hindrance limited full CEC saturation at higher loadings. Fourier transform infrared spectroscopy (FTIR) showed that the smectite framework remained intact, while band shifts in the N–H, C=O, and CH₂ regions indicated strong surfactant–clay mineral interactions and LAE® conformational changes. Thermogravimetric analysis revealed a reduction in decomposition steps from six (pure LAE®) to four upon intercalation, alongside a shift in the main decomposition peak from 285.7°C to 305.1°C for sample based on the Arizona smectite having high layer charge. Evolved gas analysis (TG-FTIR) confirmed altered degradation pathways for the organosmectites, with the suppression of nitrogen-containing volatiles such as NH₃ and NO₂. High-temperature FTIR (HT-FTIR) further demonstrated reduced molecular mobility and enhanced thermal stability, particularly in samples with the highest LAE® content. Quantitative spectral analysis showed persistent C–H, C=O, and C–N–H bands at elevated temperatures, confirming the stabilizing effect of interlayer confinement. These findings underscore the potential of LAE®-modified smectites as thermally robust, non-toxic hybrid materials with promising applications as feed additives.

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This study investigates the chemically reactive nonlinear radiative Eyring–Powell flow of nanofluids over a thin cylinder under the influence of buoyancy forces with stagnation point. The analysis incorporates the Eyring–Powell fluid model into the momentum equation to capture the viscoelastic behaviour of the nanofluid flow over an extended cylinder. The governing equations account for Brownian motion, thermophoresis effects, velocity, and thermal radiation. Dissipation and Joule heating are included to characterize the heat transfer process. For stability of problem, the theory of motile micro-organism is implemented. Further, the assumptions of buoyancy forces, mixed convection, and thermophoresis with multiple slips make the problem more interested. Similarity variables are utilized to alter the PDEs of flow model into ODEs. The reduced models of the flow problem are achieved by applying MATLAB bvp4c command. The influence of involving parameters like buoyancy ratio, Eyring–Powell parameters, Lewis number, thermophoresis, radiation parameter, Prandtl number, and chemical reaction on velocity, rotation, volumetric concentration, temperature, and density profiles is dissected via tables and graphs. The study involves two cases when (M, K=0) and (M, K=0.3) to describe fluid, accounting for both viscous and inertial effects. It is seen that thermal radiation and Prandtl number help to deteriorate heat transfer. Both the directions of fluid motion has quicken when mounting the quantity of Eyring–Powell parameter and it raises the temperature profile.

Environmental concerns and the rising demand for fossil fuels have encouraged the exploration of alternative fuels like hydrogen. Hydrogen, with its clean-burning properties, can improve engine performance and meet strict emission standards when used in a dual-fuel mode with diesel. In this study, a four-stroke single-cylinder diesel engine (SCDE) was experimentally tested under diesel–hydrogen dual-fuel operation at 20–100% load conditions. The results showed that the diesel–H₂ strategy at 7500 μs (DH3) injection strategy demonstrated a 23% improvement in brake thermal efficiency (BTE) compared to baseline diesel operation at full load, though oxides of nitrogen (NOx) emissions peaked at 7.5 g kW^-1 h^-1 at full load under the DH3 approach. Soot emissions are minimal at low loads but increase sharply at higher loads, particularly for DH3. Unburned hydrocarbon (UHC) emissions are higher for hydrogen-enriched strategies compared to pure diesel under low-load conditions, with diesel–H₂ strategy at 5500 μs (DH1) and diesel–H₂ strategy at 6500 μs (DH2) showing peaks at 29 g kW^-1 h^-1 and 22 gkW^-1 h^-1, respectively. The diesel–H₂ strategy at 8500 μs (DH4) achieved a maximum 85% reduction in UHC emissions and significantly minimized soot formation under high-load conditions. However, they also present challenges in terms of NOx emissions, particularly at higher loads. Therefore, optimizing injection strategies is critical to achieving a balance between enhanced performance and emissions compliance for sustainable engine operation. Furthermore, eight machine learning (ML) models—decision trees (DT), random forest (RF), support vector regression (SVR), gradient boosting (GB), AdaBoost (ADA), linear regression (LR), K-nearest neighbors (KNN) and ensemble learning (ENSEMBLE)—were employed for predictive analysis of performance and emissions. The ENSEMBLE model achieved the best prediction accuracy (R-squared (R²) = 0.98, lowest root mean square error (RMSE) = 0.012, mean absolute error (MAE) = 0.009), confirming its robustness and generalization capability in dual-fuel engine prediction.

In the present study, the flow, heat, and mass transfer characteristics of a bioconvective nanofluid over a stretching plate subjected to an external magnetic field are analyzed. The nonlinear slip at the surface is modeled using the Thompson–Troian velocity slip condition, while convective boundary conditions are applied to account for heat and mass transfer in the thermal and concentration fields. To ensure uniform nanoparticle distribution, motile microorganisms are incorporated into the fluid. These microorganisms help counteract particle aggregation and prevent solidification within the medium. Their motion gives rise to the bioconvection phenomenon, enhancing overall fluid transport. The governing equations for momentum, energy, and species concentration are formulated as partial differential equations (PDEs), incorporating key effects such as viscous dissipation, magnetic field influence, and heat sources. Using similarity transformations, the PDEs are reduced to a system of ordinary differential equations (ODEs). This system is then numerically solved via Python solve_bvp function, which employs a collocation method for boundary value problems. The computed solutions are validated against existing literature, and residual analysis is conducted to ensure accuracy. The results reveal that an increase in magnetic field strength suppresses fluid velocity while simultaneously raising the nanofluid temperature. Additionally, higher critical shear stress associated with the Thompson–Troian slip model further reduces the flow velocity near the surface.

Novel Zn_1-3(x+y)▢_x+yFe_2xRE_2yWO₄, where RE = Ho³⁺, Er³⁺, Yb³⁺, x = 0.005, 0 < y ≤ 0.015, and ▢ represents vacancies in the crystal lattice. Solid solutions were successfully synthesized by the traditional solid-state reaction method using ZnO, Fe₂O₃, RE₂O₃ and WO₃ as the initial reactants. Doped materials were extensively characterized by powder X-ray diffraction (XRD), differential thermal analysis-thermogravimetry (DTA-TG) methods, scanning electron microscopy (SEM–EDX), infrared (FT–IR), and ultraviolet–visible–near infrared (UV–vis–NIR) spectroscopies. The results revealed that all doped samples were phase pure with grain sizes practically not exceeding 10 µm, exhibiting uniform morphology. New materials belong to the wolframite-type structure with space group P2/c. Furthermore, activated by Fe³⁺ and RE³⁺ ions materials also demonstrated high thermal stability up to max. 1180 °C. They exhibit strong absorption in the ultraviolet range, and some of them (RE = Ho³⁺ and Er³⁺) also in the visible light. A detailed analysis of the UV–Vis–NIR spectra revealed that doped zinc tungstates possessed a direct optical band gap whose value is close to 3 eV. All these features make the new doped wolframite-type solid solutions promising candidates for multifield applications.