Journal of Thermal Analysis and Calorimetry最新文献

To examine the impact of different heating rates and oxygen concentrations on the combustion characteristics and kinetic parameters of coals at various metamorphic degrees, this study selected four different metamorphic degrees as experimental subjects. Thermogravimetric experiments were conducted under various heating rates and oxygen concentrations to obtain characteristic temperature points, mass loss rates, and heat absorption and excretion characteristics of coal samples under different conditions. Furthermore, reaction mechanism functions were determined, and the reaction kinetics "three factors" of coal samples under different conditions were calculated to ascertain activation energy. Based on characteristic temperature points, different phases of coal spontaneous combustion were delineated, and the oxidative characteristics of coal samples at each phase were analyzed. The study explored the impact mechanisms of different temperatures and oxygen concentrations on coal spontaneous combustion from the perspectives of characteristic temperature points and activation energy. The results indicate that inertization, meaning the introduction of inert gases, has an inhibitory effect on the coal–oxygen complex process for coals at different metamorphic degrees. As the degree of inertization increases, the two phases most affected are the oxygen uptake and mass gain phase and the combustion phase. Compared to the oxygen uptake and mass gain phase, the TG curve of the combustion phase shows a delayed phenomenon with increased inertization degree. With rising temperature, the overall trend of the DTG curve initially decreases, followed by an increase, and then reaches a steady plateau, with the minimum value occurring at the trough. The maximum mass loss rate of coals at different metamorphic degrees decreases with an increase in inertization degree, indicating that inertization inhibits the coal oxidation process. Additionally, the temperature points corresponding to the maximum exothermic rate all shift backward. The DSC curves of coal samples exhibit an overall trend of initial decrease followed by an increase with temperature variation. With enhanced inertization degree, the maximum exothermic rate of coals at different metamorphic degrees decreases, and the corresponding temperature points shift backward. As the inertization intensity decreases, the activation energy (E_a) of the low-temperature oxidation phase generally decreases for coals at four different metamorphic degrees. Under the same inertization intensity, coals with higher metamorphic degrees have higher activation energy. This study can provide theoretical support for the prevention and control of coal spontaneous combustion.

This research presents an experimental assessment of exergy and entropy generation in a straight circular multi-microchannel stainless steel heatsink. Deionized water and water/alumina nanofluids with 1–4% (m/m) concentrations are used as cooling fluids in the heat sink, operating at low Reynolds numbers (10 ≤ Re ≤ 50). The primary goals of the exergy analysis are to evaluate the first and second laws of thermodynamics, including exergy output, gain, and loss. Entropy generation analysis encompasses both heat transfer and flow entropy. The study’s main innovation is the examination of exergy and entropy generation in microchannel heat sinks using nanofluids at low Reynolds numbers. The results show that nanofluids with a 4% nanoparticle concentration achieve a higher exergy gain of 56% compared to DI water at Re = 40. Exergy loss increases with Reynolds numbers and with increase in the nanoparticles concentration up to 4%, the exergy loss increases up to 27% at Re = 10. Back conduction, significant at low Reynolds numbers, does not affect the second law efficiency. The highest second law efficiency occurs at Re = 10, with DI water achieving 7.2% under high heat flux, while nanofluids with 4% nanoparticle concentration show 5.9%. This efficiency decreases with Reynolds number and nanoparticle concentrations. However, introducing alumina nanoparticles into DI water reduces entropy generation; at Re = 50, the total entropy generation is 0.0013 W K⁻¹ for DI water and 0.001 W K⁻¹ for nanofluids with a 4% nanoparticle concentration. Nanofluids reduce entropy generation up to 27% at a 4% concentration of nanoparticles compared to DI water at Re = 40. These findings offer valuable insights for optimizing the design and performance of microchannel heat sink configurations for various thermal management applications, focusing on exergy and entropy generation.

The residual coal is prone to oxidation in different degrees after being immersed-dried in waterlogged goafs, but the reignition characteristics of water-immersion coal by low-temperature pre-oxidation remain unclear. Herein, lignite was pre-oxidized to 40 °C, 80 °C, 120 °C, 160 °C, 200 °C, and 230 °C after 60 days of immersion. Moreover, the microstructure changes of water-immersed lignite after oxidized were investigated using low-temperature nitrogen adsorption and infrared spectroscopy, and its spontaneous combustion characteristics were assessed employing thermogravimetry. The results displayed that the pore volume, specific surface area, and pore diameter increased and then decreased as the pre-oxidation temperature rose. Specifically, lower temperatures (below 80 °C) promoted the formation of micropores and mesopores, as well as the merger and transformation of pores into macropores, which facilitates the diffusion and adsorption of oxygen. However, higher temperature oxidation (> 200 °C) reduced both the number of pores and the content of reducing functional groups (–OH, –CH₃, and –CH₂). Comparatively, the lignite oxidized at 80 °C maintained a strong chemical reactivity owing to the high relative content of -CH₂ and C = O. Furthermore, the pre-oxidation treatment mainly affected the thermal decomposition and gas-phase combustion of the water-immersed coals. Moreover, as the degree of oxidation rose, the characteristic temperatures (T₂–T₄) and the activation energy first decreased and then increased, while the comprehensive combustion index exhibited an opposite trend. Notably, the critical oxidation temperature of 80 °C is a turning point for the above change. Thus, the pre-oxidation at 80 °C heightens the risk of reignition in water-immersion coal owing to its developed pore structure and abundant active groups. It is imperative to avoid the critical temperature during low-temperature oxidation of water-immersed coals.

The present work examines numerically the natural convection along with the entropy generation within H-shaped enclosure with wavy walls filled by (Ag-MgO/water) hybrid nanofluid considering inner bodies and under the influence of horizontal magnetic field and thermal radiation using finite element scheme. The inner bodies of the circular shapes are kept at a hot temperature, while the two-sided wavy walls are kept at a cold temperature. The rest of the enclosure’s walls are thermally insulated. The influence of many parameters had been examined such as Rayleigh number (({10}^{3}le text{Ra}le {10}^{5})), Hartmann number (left(0le text{Ha}le 60right)) vertical location of inners bodies (left(0.2le delta le 0.8right)), distance between inner bodies (left(0.3le Ele 0.9right)), height of the enclosure walls (left(0.2le Ble 0.8right)) and width of the enclosure wall (left(0.1le Ale 0.9right)) in addition to the radiation parameter (left(0le text{Rd}le 3right)) on fluid flow, heat transfer and entropy generation. The results of this study had been presented in terms of streamlines, isotherms, entropy generation, Nusselt and Bejan number. The results showed that the Nusselt number will be at its lowest value when the vertical location of the inner bodies is (left(delta =0.8right)) and the influence of Hartmann number will be negligible at this value. Also, at high Rayleigh number (left(text{Ra}={10}^{5}right)) increasing the distance between the inner bodies from (left(E=0.3right)) into (left(E=0.9right)) leads to increasing Nu by (76%). However, increasing the height of the enclosure’s walls from (left(B=0.2right)) into (left(B=0.8right)) leads to enhancing Nu by (0.02%.) However, increasing width of the enclosure wall from (left(A=0.1right)) into (left(A=0.9right)) leads to an obvious reduction in Nusselt number by (20%). Additionally, it had been obtained that increasing the vertical location of the inner bodies, the distance between them and the width of the enclosure and reduction of the height of the enclosure’s wall lead to increasing Bejan number. Stronger magnetic fields enhance conductive heat transfer; increasing the Bejan number which represents irreversibility as noted at increasing Hartmann number from (left(text{Ha}=0right)) into (left(text{Ha}=60right)) leads to increasing Bejan number by (79%).

Currently, it is widely recognized by scholars that nanocatalytic materials with high dispersity have a better catalytic effect on the thermal decomposition of energetic materials. However, there are significant challenges in exploring the relationship between the dispersity and catalytic performance of NCMs in NCMs/EMs, and with the literature rarely reported. In this study, we established a quantitative calculation method for the dispersity index of NCMs in NCMs/EMs composites based on the differential UV absorption between NCMs and EMs. Subsequently, we prepared CuCr₂O₄ (CCO)/raw ammonium perchlorate (AP) and CCO/fine AP composite with different dispersity using mechanical mixing and ultrasonic mixing techniques. Their formation was confirmed through X-ray diffraction (XRD), scanning electron microscopy (SEM) and particle size analysis. Solid UV tests demonstrated the highest repeatability of the UV absorption peaks near the wavelength of 212 nm. By measuring the absorbance at 212 nm for different nano-CCO/AP composite, the solid UV values were obtained. The dispersity index for different samples was calculated using the dispersity calculation method. Furthermore, differential scanning calorimetry (DSC) tests were conducted on nano-CCO/AP composite samples with different dispersity. The results indicated that the higher the dispersity index of nano-CCO, the better promotion of thermal decomposition on AP (more advance in high-temperature decomposition peak). Finally, the application of nano-CCO/AP composites with different dispersity in solid propellants verified the positive correlation between the dispersity of NCMs and their catalytic performance. This study lays the foundation for establishing a new strategy to evaluate the dispersity of NCMs and is expected to lead the trend of the application of NCMs in the field of EMs.

Considering the randomness of the fire location and the high probability of tunnel fires occurring near the tunnel portal, a series of experiments were conducted using a 1:15 tunnel model. In the event of double fires with an extra external fire source except for the internal fire source, the characteristics of smoke spread and smoke stratification are influenced by asymmetric flow fields. The distribution and decay of the smoke temperature beneath the tunnel ceiling, the smoke layer thickness, and the smoke layer stratification were measured and analyzed. The findings indicate that despite a considerable dimensionless fire spacing, the maximum temperature remains longitudinally positioned between the two fire sources. The characteristics of temperature attenuation showed the variation with the dimensionless fire spacing, particularly when the fire spacing was minimal. Furthermore, a model of the pre-exponential factor was built. There was a stable area of smoke layer thickness upstream of the internal fire, showing no sensitivity to variations in dimensionless fire spacing or pool size. Additionally, an obvious smoke interface drop was found between two fire sources.

This paper investigates the impact of the gas generator on the heat transfer of pyrotechnics. The enhancement effect is examined using a combination of experimental and engineering methods. The results demonstrate that the pyrotechnics exhibit favorable thermal performance based on performance testing. The heat transfer efficiency of the pyrotechnics can be enhanced by adjusting the structure of the gas generator, including the filter and gas outlet, as well as the shape of the pyrotechnics. However, regardless of the structure, there is a maximum peak where the gas generator achieves the highest rate of heat transfer enhancement for the pyrotechnics. Through analysis of the heat transfer experiment process, it can be concluded that the gas generator effectively reduces the heat transfer time of the pyrotechnics and minimizes heat loss during the process. Even when using coolant, the heat transfer efficiency of the pyrotechnics remains high at 69.31% after the gas generator enhancement.

The study addresses the design and optimization of chemical composition and processing routes of new quenching and partitioning medium-Mn alloy using theoretical and experimental approaches. The thermodynamic calculations using Thermo-Calc and JMatPro software were carried out to characterize the influence of Mn, Si and Al contents on cementite formation and precipitation processes. The evolution of individual phases as a function of temperature under thermodynamic equilibrium conditions was estimated. The investigations included the determination of continuous cooling transformation (CCT) and the time–temperature transformation (TTT) diagrams of a model 4Mn alloy. The calculated equilibrium diagrams were compared with the experimental diagrams determined using dilatometric tests. Microstructural observations were carried out to verify the results of dilatometric measurements. The results of thermodynamic calculations and experimental tests showed the moderate agreement. It is related to the inaccuracy of currently available models in the used software and/or non-equilibrium conditions of experimental tests.

Owing to improved thermal performances and stable features, the hybrid nanomaterials claim novel applications in the heat transfer enhancement, solar energy, chemical processes, cooling processes, etc. The hybrid nanomaterial is the decomposition of aluminum and copper nanoparticles subject to water base liquid. The aim of current analysis is to develop a fractional model for the natural convective flow of hybrid nanofluid confined by a channel with uniform walls. The thermal properties of hybrid nanofluid is justified by utilizing the aluminum and copper nanoparticles. The water is used as a base fluid. The flow is further influenced by mixed convection applications. For fractional model, the computations are performed by using Prabhakar model. The motivations for implementing the Prabhakar fractional model are due excellent accuracy. The integration technique is followed with help of Laplace algorithm. The inverse numerical integration of the problem with implementation of Laplace technique has been suggested by using the Zakian, Stehfest, and Tzou’s numerical algorithms. The influence of parameters is observed with physical interpretation. It has been noticed that velocity profile reduces by increasing nanoparticles volume fraction. Change in fractional parameter leads to enhancement of temperature profile.

Cancer diseases are one of the most common causes of death. It is important to reduce the proliferation of cancer cells at an early stage, but also to limit their migration. There is a need to find new compounds of moderate anticancer prevention activity for long administration. TOPIIα and actin are proteins that in states of inflammation can cause the progression of cancer and neoblastic cell migrations. Looking for compounds that will work comprehensively in preventing cancer, interacting with both TOPIIα and actin is crucial/was our aim. In this study, the antioxidant properties of propenylbenzene derivatives and their affinity to bind actin and TOPIIα causing inhibition of their functions were evaluated. The ligand–protein binding assay was carried out by isometric titration calorimetry (ITC), and molecular docking, and the antioxidant potential. The highest chelation activity was shown by 5b: 83.95% (FRAP 18.39 μmol Fe(II) mL⁻¹). High affinity for actin and TOPIIα using ITC and docking was shown by diol forms. For actin the best ligands were 2b (∆H − 51.49 kJ mol⁻¹, ∆G − 27.37 kJ mol⁻¹) and 5b (∆H − 17.25 kJ mol⁻¹, ∆G − 26.20 kJ mol⁻¹), whereas for TOPIIα: 3b (∆H − 163.86 kJ mol⁻¹, ∆G − 34.60 kJ mol⁻¹) and 5b (∆H − 160.93 kJ mol⁻¹, ∆G − 32.92 kJ mol⁻¹). To confirm the occurrence of the interactions at the active site of the proteins, molecular docking and subsequent molecular dynamics simulations were performed, which showed for both actin and TOPIIα the highest enthalpy of interactions of 5b: − 34.94 kJ mol⁻¹ and − 25.52 kJ mol⁻¹, respectively.