Journal of Thermal Analysis and Calorimetry最新文献

Solar desalination remains a practical solution for freshwater scarcity, yet the productivity of conventional systems often falls short. This study introduces an enhanced pyramidal solar still (EMPSS) that integrates a 340 mT magnetic field with a low-voltage electric field (12–24 V) to improve evaporation and condensation performance. Two identical units—a conventional pyramid solar still (CPSS) and the modified EMPSS—were tested outdoors under Baghdad’s climatic conditions. The pyramidal geometry, with its wide condensation surface and reduced shading, provided a stable baseline for comparison. Results show that magnetic activation increased the water–glass temperature difference from 4.5 to 7.7 °C and raised the basin temperature to 54.6 °C, yielding a 29.3% increase in productivity. When the electric field was added, the system achieved a maximum hourly yield of 684 mL m⁻² at 24 V, while daily production increased by 47.6% (12 V) and 66.5% (24 V). These improvements are linked to enhanced heat transfer, reduced surface tension, and altered water-molecule dynamics under electromagnetic influence. Material selection also played a key role in system performance. The findings highlight a practical pathway for substantially upgrading pyramidal solar stills through combined electromagnetic fields, encouraging further exploration of field configurations, alternative materials, and hybrid desalination integrations.

The importance of drilling in the development and exploitation of oil and gas reservoirs is very vital and is one of the most costly tasks in the extraction of underground resources. For drilling, a drilling fluid is needed that can perform tasks such as cleaning the drill tip, cooling the drilling site, and transporting the cut rocks from inside the well to the outside. Since the fluids used in this field are non-Newtonian fluids, the drilling mud flow inside the well can be simulated as a non-Newtonian turbulent flow in order to study the hydrodynamics of the drilling fluid flow and to investigate the conditions for improving drilling performance. In this research, a numerical study of the turbulent flow of the non-Newtonian fluid water and carboxymethyl cellulose around a rotating cylinder was conducted. The purpose of this project is to investigate the fluid velocity field calculated by different turbulence models under these conditions. The main turbulence model considered for this study will be the (k- varepsilon text{RNG}) model, which is one of the most commonly used models for turbulent flow, and the results obtained from this model will be compared with other turbulence models including (k-omega text{SST}), large-eddy simulation, Spalart–Allmaras, Reynolds stress turbulence model, and SST transition. For this purpose, computational fluid dynamics (CFD) software will be used to calculate and obtain the desired responses. The results obtained using the method used in this study show a good agreement with the experimental results. It was also observed that the different turbulence methods provided responses close to each other. This research provides a new criterion for evaluating the accuracy of turbulence models in non-Newtonian fluid flow conditions and helps to better understand the interaction between viscoelastic effects and turbulence. In addition, the results are useful as a guide to selecting the most optimal turbulence model based on the required accuracy and computational constraints in industries such as food, pharmaceutical, and petrochemical.

Installing vortex generators within heat transfer channels is one of the effective methods to enhance the heat transfer rate of fluids in pipes and passages. This approach holds significant importance for alleviating global energy constraints and achieving efficient energy utilization. By inducing fluid rotation around an axis, vortex generators can form vortices within pipes, thereby improving heat transfer efficiency and becoming a key focus in current energy-saving research. Despite extensive research on vortex generators in recent years, comprehensive reviews and summaries of their structures and types remain relatively scarce. This review systematically organizes the progress in traditional wing angle vortex generator research and focuses on comparing the heat transfer performance of various novel structures under different Reynolds number conditions. It aims to provide a comprehensive evaluation of the structural characteristics and application effectiveness of vortex generators, offering theoretical references and research insights for the subsequent development and optimization of related technologies.

The article presents a method for determining the thermal power of a LED COB module as a critical parameter for engineering the cooling systems of high-power LED luminaires. The research problem is the lack of simple yet accurate analytical models of thermal operating regimes for high-power LED modules that are suitable for rapid engineering assessment and embedded controllers. This is important because incorrect estimation of heat dissipation leads to excessive junction temperatures, reduced luminous efficacy, and shortened service life. The novelty lies in a physics-informed selection and comparison of four regression models—linear, with exponential and logarithmic temperature terms, and a bivariate quadratic form—with explicit inclusion of the second-order interaction between temperature T and current I. Experiments were conducted over ambient temperatures from − 30 to + 40 °C and drive currents from 1 to 5 A with fixed step sizes; regression models were fitted to measured electro-photometric quantities, and their accuracy and computational cost were assessed. The results show a monotonic increase of thermal dissipation with increasing T and I, as well as a statistically significant T⋅I interaction. The quadratic regressor provided the best accuracy–complexity trade-off, achieving RMSE≈0.8 W and a mean relative error < 1% across the entire operating window. Accounting for second-order terms and the T⋅I interaction is necessary for an adequate description of thermal losses in high-power LEDs. The proposed quadratic model is a practical surrogate for engineering use (thermal regime calculations, boundary/source terms in CFD, and LED driver firmware).

This paper investigates the mechanism of entropy generation in unsteady electroosmotic Cross fluid flow, modeled as blood, under the Debye–Hückel approximation through a porous horizontal microchannel with mild overlapping stenoses. The study incorporates a variable viscosity model (variable hematocrit). The finite difference technique is employed to solve the system of nonlinear governing equations. The results illustrate the impact of various parameters on velocity, temperature, concentration, and entropy production profiles. A significant finding is that increasing the hematocrit parameter reduces blood velocity due to the higher concentration of red blood cells. Additionally, an increase in the Joule heating parameter results in higher entropy generation.

Molecular explosives such as RDX (1,3,5-Trinitroperhydro-1,3,5-triazine) and HMX (1,3,5,7-Tetranitro-1,3,5,7-tetrazocane) have seen increasingly widespread use in various applications for decades since their discovery and synthesis. These explosives are used either in pure form or in various mixtures, including composite explosives, polymer-bonded explosives (PBXs), and cocrystals. Therefore, studying the thermal behavior and responses to temperature changes for explosives RDX and HMX is remains of significant interest to producers, consumers, and researchers. Common methods of thermal analysis, such as thermogravimetry (TG), differential thermal analysis (DTA), and differential scanning calorimetry (DSC) in both isothermal and non-isothermal procedures are used to investigate thermal behavior. In this review, the results of thermal behavior studies of RDX and HMX in their pure form, and in composites, PBXs, cocrystals, also, in the presence of additives have been presented and analyzed. Kinetic parameters and the mechanism of thermal decomposition reactions are evaluated and discussed.

Thermogravimetry coupled to Fourier-transform infrared spectroscopy (TGA/FTIR) was used to analyze the evolved gases from pyrolysis of four different lignocellulosic fibers (abaca, hemp, henequen, and coconut) that contain variable percentages of cellulose, hemicellulose and lignin. TGA results revealed that although the fibers exhibited different thermal stabilities (henequen had the highest decomposition temperature while coconut reported the lowest), the thermal decomposition pattern was similar as all samples displayed two degradation stages. By comparing representative spectra of the evolved gases at each stage for all-natural fibers, it was observed that during the first emission, the released gases were different and varied depending on fiber type. In contrast, during the second emission, similar spectra were obtained for all-natural fibers. Thus, it was found that during the first stage, abaca fibers release mainly carbon dioxide, hemp fibers evolve gases containing hydroxyl and carbonyl functionalities, whereas henequen and coconut ones produce carbon dioxide and gases that contain compounds possessing carbonyl and hydroxyl functional groups. During the second stage, all samples released carbon dioxide as well as compounds containing carbonyl, hydroxyl, and aliphatic functional groups.

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A new set of Research Grade Test Materials (RGTMs) has been developed for accurate temperature calibration in high-temperature differential scanning calorimetry (DSC) and differential thermal analysis (DTA). The candidate eutectic binary alloys and their melting temperatures (m.p.) are Ni-41Nb (The alloy compositions are presented as mole fraction percentages, and the purity of elements and alloys is represented in mass fraction percentages) (1181 °C), Co-13Nb (1240 °C), Fe-10Nb (1372 °C), Rh-23.5Si (1421 °C), and Ru-28Si (1535 °C). This set of calibration alloys will cover the temperature range between the melting points of gold (1064 °C) and nickel (1455 °C) and help eliminate uncertainties caused by the oxidation of Ni and its eutectic reaction of L (Ni) + NiO. Additionally, DSC/DTA instruments that require intermediate temperature calibration between gold and nickel can now accurately perform temperature calibration using these new RGTMs. After calibrating with RGTMs instead of Ni, the estimated variance has improved from 9.16 to 0.65 °C.

Polysaccharides derived from Pleurotus eryngii (P. eryngii), among the most important bioactive components found in mushrooms, exhibit a range of health-promoting functions. This study focuses on cultivating probiotic strains, namely Lactobacillus plantarum (L. plantarum) and Kluyveromyces marxianus (K. marxianus). It investigates their growth and proliferation in the presence of P. eryngii polysaccharides (PEP). In addition, the influence of different irradiation sources (γ-rays, pulsed light, light-emitting diodes, LEDs, and cold cathode fluorescent lamps, CCFLs) and doses on irradiated PEP and their subsequent effects on microbial growth were examined. Irradiation altered the molecular structure of PEP, as reflected in changes in moisture desorption, gelation, and thermal decomposition behavior determined by differential scanning calorimetry (DSC). Non-irradiated and light-irradiated PEP functioned as utilizable carbon sources in the medium for L. plantarum under the present in vitro conditions, as demonstrated by isothermal microcalorimetry (TAM Air) tests. The growth curves indicated that L. plantarum can metabolize P. eryngii polysaccharides, although the magnitude of growth enhancement depended on the glucose concentration and irradiation dose. In control groups, media containing 1% glucose generally outperformed PEP-only media, suggesting that excessively high sugar concentrations may hinder growth. In contrast, complete replacement of glucose by PEP (PEP2) led to lower growth enthalpy than glucose-containing controls. Furthermore, adding PEP did not significantly enhance growth in K. marxianus medium, particularly when glucose was replaced entirely. Overall, PEP appears suitable for partial replacement of glucose as a carbon source in the medium for L. plantarum under these experimental conditions. In contrast, complete replacement resulted in reduced growth compared with glucose-containing controls. K. marxianus was more sensitive to carbon source selection, and the glucose concentration in the medium directly affected its growth. These findings are based on single strains of L. plantarum and K. marxianus in controlled in vitro cultures, and further in vivo and multi-strain studies are required before concluding prebiotic effects in humans.

The effectiveness and the performance of SAHs for drying fruits are examined in this article in different Moroccan regions renowned for fruit drying, each characterized by distinct climates: humid Mediterranean (Al Hoceima), semi-arid (Meknes), arid (Marrakech), and desert (Ouarzazate). The regions are known for drying figs, prunes, apricots, and dates, respectively. The study examines the efficiency of two thermal storage units: sensible and latent using granite and PCM, respectively. The investigation focuses on the ideal temperature needed for drying in each region. Using a C++ function, actual climate data for the warmest day of summer 2023 were inserted into the simulation software. The results show that in Meknes and Marrakech, it is strongly recommended to use the PCM as a storage unit to maintain the optimum temperature range for drying. However, in Al Hoceima and Ouarzazate, it is recommended not to use the PCM, as the temperature drops considerably during the day. The PCM extends the drying process by around 2, 3, and 4 h in Al Hociema, both in Meknes and Marrakech and in Ouarzazate, respectively. Besides, in terms of humidity and temperature, Meknes found to be the most suitable region in Morocco for drying.