Search Results (426)

Cooling crystallization experiments of curcumin in isopropanol confirmed that curcumin can crystallize via classical or nonclassical pathways, depending on the levels of supersaturation and supercooling. Light microscopy analysis revealed that classical crystallization produces needle-shaped single crystals with an equilibrium habit, while nonclassical crystallization results in spherulitic mesocrystals. Through a series of experiments under various conditions, we developed a crystal habit phase diagram for curcumin in pure isopropanol. Presented here for the first time, this diagram illustrates the relationship between supersaturation, supercooling, and crystal habit, offering a valuable guide for controlling curcumin crystallization pathways. Full article

In the context of global climate change, changes in unfrozen water content in permafrost significantly impact regional terrestrial plant ecology and engineering stability. Through Differential Scanning Calorimetry (DSC) experiments, this study analyzed the thermal characteristic indicators, including supercooling temperature, freezing temperature, thawing temperature, critical temperature, and phase-transition temperature ranges, for silt loam with varying starting moisture levels throughout the freezing and thawing cycles. With varying starting moisture levels throughout the freezing and thawing cycles, a model describing the connection between soil temperature and variations in unfrozen water content during freeze–thaw cycles was established and corroborated with experimental data. The findings suggest that while freezing, the freezing and supercooling temperatures of unsaturated clay increased with the soil’s starting moisture level, while those of saturated clay were less affected by water content. During thawing, the initial thawing temperature of clay was generally below 0 °C, and the thawing temperature exhibited a power function relationship with total water content. Model analysis revealed hysteresis effects in the unfrozen water content curve during freeze–thaw cycles. Both the phase-transition temperature range and model parameters were sensitive to temperature changes, indicating that the processes of permafrost freezing and thawing are mainly controlled by ambient temperature changes. The study highlights the stability of the difference between freezing temperature and supercooling temperature in clay during freezing. These results offer a conceptual framework for comprehending the thawing mechanisms of permafrost and analyzing the variations in mechanical properties and terrestrial ecosystems caused by temperature-dependent moisture changes in permafrost. Full article

The growing global energy demand, coupled with environmental concerns, necessitates the development of efficient energy storage technologies. Phase Change Materials (PCMs) have emerged as a promising solution for thermal energy storage (TES) due to their ability to store and release latent heat during phase transitions. This review provides a comprehensive analysis of PCMs, exploring their classifications based on phase transition types, chemical compositions, and thermophysical properties. Additionally, the review highlights advancements in developing organic, inorganic, and metallic PCMs and evaluates their potential applications in sectors such as solar energy, construction, and automotive industries. Methodologies include a detailed examination of the strengths, limitations, and solutions to challenges such as low thermal conductivity, phase separation, and supercooling. The results summarize the diverse applications of PCMs, emphasizing their critical role in enhancing energy efficiency and sustainability. The review concludes with recommendations for overcoming current limitations and future directions for PCM research and technology integration across various industries. Full article

Aceclofenac (ACF), a non-steroidal anti-inflammatory drug, was obtained in its amorphous state by cooling from melt. The glass transition was investigated using dielectric and calorimetric techniques, namely, dielectric relaxation spectroscopy (DRS), thermally stimulated depolarization currents (TSDC), and conventional and temperature-modulated differential scanning calorimetry (DSC and TM-DSC). The dynamic behavior in both the glassy and supercooled liquid states revealed multiple relaxation processes. Well below the glass transition, DRS was able to resolve two secondary relaxations, γ and β, the latter of which was also detectable by TSDC. The kinetic parameters indicated that both processes are associated with localized motions within the molecule. The main (α) relaxation was clearly observed by DRS and TSDC, and results from both techniques confirmed a non-Arrhenian temperature dependence of the relaxation times. However, the glass transition temperature (T_g) extrapolated from DRS data significantly differed from that obtained via TSDC, which in turn showed reasonable agreement with the calorimetric T_g (T_g-DSC = 9.2 °C). The values of the fragility index calculated by the three experimental techniques converged in attributing the character of a moderately fragile glass former to ACF. Above the α relaxation, TSDC showed a well-defined peak. In DRS, after “removing” the high-conductivity contribution using ε’ derivative analysis, a peak with shape parameters α_HN = β_HN = 1 was also detected. The origin of these peaks, found in the full supercooled liquid state, has been discussed in the context of structural and dynamic heterogeneity. This is supported by significant differences observed between the FTIR spectra of the amorphous and crystalline samples, which are likely related to aggregation differences resulting from variations in the hydrogen bonds between the two phases. Additionally, the pronounced decoupling between translational and relaxational motions, as deduced from the low value of the fractional exponent x = 0.72, derived from the fractional Debye–Stokes–Einstein (FDSE) relationship, further supports this interpretation. Full article

Diapause, a survival strategy utilized by many insects under severe environmental conditions, can generate costs that potentially affect post-diapause development and reproduction. The willow leaf beetle, Plagiodera versicolora, overwinters as an adult. This study investigated the cold hardiness-hardiness and energy utilization of female P. versicolora, and their impact on post-diapause reproductive fitness. The supercooling point exhibited seasonal temperature variation, with the lowest points occurring in January and February, coinciding with the relatively lower ambient temperatures. Lipid content demonstrated a pronounced decline at the onset of diapause (from November to December) and stabilized from December to March. Glycogen content also showed a sharp decrease from November to January, subsequently stabilizing at relatively constant levels. In addition, trehalose content increased significantly when temperatures dropped (from November to January) and then decreased as temperatures rose (from January to March). There were no significant differences in the time from pairing to successful mating for post-diapause females compared with non-diapause females. However, mating duration and the pre-oviposition period for post-diapause individuals relative to non-diapause individuals increased, coupled with a reduction in the oviposition period, total number of eggs, number of egg clutches, and number of eggs per clutch; however, most importantly, there was no notable change in egg-hatching success. These results suggest that the cold-hardiness strategy of P. versicolora falls within the freeze-avoidance category, with energy usage predominantly reliant on lipids and carbohydrates during diapause initiation. Our findings also highlight that, although post-diapause females are capable of nutrient replenishment, the energetic demands of diapause result in considerable negative impacts on post-diapause female reproductive fitness. Full article

This paper describes the development of an ice creation model to be used within the framework of a model-based systems engineering approach to predict the amount of ice growing on aircraft wings during flight. This model supports the preliminary design of the ice protection system, as well as the implementation of a control system, in real-time. When the aircraft meets a high concentration of super-cooled water in the atmosphere and a low temperature, the risk of ice formation on its external surfaces is significant. This causes a decrease in aerodynamic performance, with potential loss of control of the aircraft. To mitigate this effect, ice prevention and protection systems are crucial. The characteristics of the icing phenomena are first defined, then their effects on aircraft behavior during operation are evaluated. This allows us to develop a highly parametric predictive model of the actual icing conditions experienced by the aircraft during a given flight mission. To precisely predict the ice accretion and to design an ice protection system, estimating heat fluxes involving the aircraft’s wing surfaces and the external environment is required. To allow for this, this study also develops a thermal model that is specifically applied to the above-mentioned analysis. This model includes many factors characterizing the atmospheric conditions responsible for ice creation upon the aerodynamic surfaces, and it enables an accurate estimation and quantification of all the parameters necessary to design an appropriate ice protection system. Full article

Cold tolerance is a key factor shaping the survival and geographic distribution of terrestrial snails, especially in regions with harsh winters. Understanding how these organisms cope with freezing temperatures is crucial for predicting their responses to changing climates. This study focused on two microsnail species, Vertigo antivertigo and V. moulinsiana, to assess their winter activity, cold tolerance strategies, and whether their body size varies with latitude. Activity patterns were observed under controlled temperatures (0 °C, 2 °C, and 5 °C), while supercooling points (SCP) were measured to evaluate freezing avoidance. Shell morphology was analyzed across populations from various sites in Poland to explore local adaptations. The results showed that snail activity decreases as temperatures drop, with the lowest activity observed at 0 °C. Both species displayed a freezing-avoidant strategy, with V. moulinsiana having slightly higher SCP values, reflecting its adaptation to milder climates. Morphological differences in shell dimensions across sites suggest potential local adaptations to environmental conditions. These findings highlight temperature as a critical driver of activity, survival, and morphological variation in terrestrial snails. Limited winter activity may allow foraging or shelter-seeking but poses risks for overwintering. As climate change leads to snow-free winters, these species may face significant challenges in maintaining their populations and distributions. Full article

Wind turbines operating in high-altitude and cold regions are susceptible to icing phenomenon, which is a serious threat to the power generation efficiency and operational safety. On the basis of the current research on supercooled droplet icing, mixed-phase icing is investigated. Based on icing numerical simulations under mixed-phase conditions, the aerodynamic characteristics of wind turbine airfoils before and after icing are analyzed. The results indicate that as the icing thickness increases, the aerodynamic characteristics of the airfoil gradually deteriorate, with the lift decreasing by 40.2% and the drag increasing by 135.2%. The aerodynamic characteristics of airfoil after icing are analyzed under both glaze and rime ice conditions and compared to those of the clear airfoil. The results show that icing leads to a decrease in the lift coefficient and an increase in the drag coefficient of the airfoil. This deterioration is primarily due to the fact that icing causes premature separation of the airfoil airflow, and icing can cause obstruction at the leading edge, which leads to the formation of local vortices and a decline in aerodynamic performance. The effects of icing on the aerodynamic characteristics of wind turbine airfoils under glaze and rime ice conditions are compared, and the lift-to-drag ratio decreases by 87.9% under the glaze ice condition and by 62.4% under rime ice conditions. The results show that the effects of mixed-phase icing under glaze ice conditions has a more severe impact than under rime ice conditions. Full article

With the advancement of science and technology, wind power generation has been widely adopted globally. However, ice accretion severely limits the operational efficiency and structural safety of wind turbines in cold regions, while existing research primarily focuses on the impact of supercooled droplets on blade icing, the influence of ice crystals in cold environments on the blade icing process has been largely overlooked. This study systematically simulated the accretion of ice crystals and supercooled droplets under clear ice conditions. It evaluated the effects of various ice crystal parameters on the icing process using Fensap-Ice, which is an advanced icing simulation tool. The results indicate that ice accretion, driven by the combined action of ice crystals and supercooled droplets, weakened ice corners, making the ice shape smoother and fuller. When the angle of attack of the ice-covered airfoil exceeded 15°, a separating vortex formed on the suction side of the blade, leading to a reduction in the lift coefficient. The findings of this study highlight the critical role of ice crystals in the icing process and provide a scientific foundation for understanding the icing mechanism under complex meteorological conditions. Full article

Traditional rooftop greenhouses offer a promising solution for urban vegetable supply but have the disadvantages of overheating during the daytime and supercooling during the nighttime. To address these issues, a novel solar greenhouse system using nanofluid spectral splitting and phase change materials (NSS-PCMs) was developed. In this study, a 75-day thermal environment test experiment was conducted on the novel solar greenhouse, and the growth status and nutrient composition of three typical plants were evaluated. By optimizing the greenhouse structure parameters through the model, over 80% of 300–800 nm wavelengths for vegetable photosynthesis were transmitted to the greenhouse, while the remaining spectrum was used for heat storage to maintain warmth during nighttime. The novel solar greenhouse reduced daytime temperatures by 5.2 °C and increased nighttime temperatures by 6.9 °C, reaching a maximum thermal efficiency of 53.4% compared to traditional greenhouses. The 75-day temperature detection showed that optimal temperature ranges were maintained for approximately 60 days, both during daytime and nighttime, with an 80% assurance rate. The growth rates of three vegetables in the novel solar greenhouse improved by 55%, 35%, and 40%, and the nutrient composition doubled compared to the control group. Full article

We present thermodynamic properties for liquid uranium obtained from classical molecular dynamics (MD) simulations and the first-principles theory. The coexisting phases method incorporated within MD modeling defines the melting temperature of uranium in good agreement with the experiment. The calculated melting enthalpy is in agreement with the experimental range. Classical MD simulations show that ionic contribution to the total specific heat of uranium does not depend on temperature. The density of states at the Fermi level, which is a crucial parameter in the determination of the electronic contribution to the total specific heat of liquid uranium, is calculated by ab initio all electron density functional theory (DFT) formalism applied to the atomic configurations generated by classical MD. The calculated specific heat of liquid uranium is compared with the previously calculated specific heat of solid γ-uranium at high temperatures. The liquid uranium cannot be supercooled below T_sc ≈ 800 K or approximately about 645 K below the calculated melting point, although, the self-diffusion coefficient approaches zero at T_D ≈ 700 K. Uranium metal can be supercooled about 1.5 times more than it can be overheated. The features of the temperature hysteresis are discussed. Full article

To provide insight into the interface structure in Ti particle-reinforced Mg matrix composites, this study investigates the inherent Mg/Ti interface structure formed during the solidification of supercooled Mg melt on a (0001)Ti substrate using ab initio molecular dynamics (AIMD) simulations and density function theory (DFT) calculation. The resulting interface exhibits an orientation relationship of ${\left(0001\right)}_{\mathrm{Mg}}{//\left(0001\right)}_{\mathrm{Ti}}$ with a lattice mismatch of approximately 8%. Detailed characterizations reveal the occurrences of ${\left(0001\right)}_{\mathrm{Mg}}$ plane rotation and vacancy formation to overcome the lattice mismatch at the inherent Mg/Ti interface while allowing Mg atoms to occupy the energetically favorable hollow sites above the Ti atomic layer. The atomic diffusion behaviors of rare-earth elements Gd and Y at the Mg/Ti interface was examined using the climbing image nudged elastic band (CI-NEB) method, demonstrating a strong segregation tendency towards the interface promoted by the inherent interface structure. Additionally, the calculated Griffith work indicates enhanced interfacial adhesion due to the segregation of Gd and Y, which is beneficial for the mechanical properties of the composite. Full article

Bulk metallic glasses (i.e., BMGs) have attracted a lot of research and development interest due to their unique properties. Embedding BMG composites with nanocrystals can further extend their applications. In this study, Ta-nanocrystal-embedded metallic glass powder was prepared via the mechanical alloying of (Cu₆₀Zr₃₀Ti₁₀)₉₁Ta₉ composition for 5 h using starting elemental powders. The structural evolution during the mechanical alloying process was examined using X-ray diffraction, scanning electron microscopy, synchrotron extended X-ray absorption fine structure, transmission electron microscopy, and differential scanning calorimetry. The 5 h as-milled powder was then consolidated into a bulk sample using vacuum hot pressing with an applied pressure of 0.72, 0.96, and 1.20 GPa. The effects of the applied pressure during vacuum hot pressing on the structure of the obtained BMG were investigated. The experimental results show that Ta-nanocrystal-embedded metallic glass composite powder was prepared successfully after 5 h of mechanical alloying. The 5 h as-milled composite powder exhibited a large supercooled region of 43 K between the glass transition temperature of 743 K and the crystallization temperature of 786 K. Using vacuum hot pressing at 753 K for 30 mins with an applied pressure, dense nanocrystal-embedded BMG composites were synthesized. The relative density and the crystallization temperature of the BMG composites increased with increasing applied pressure. The nanocrystal-embedded BMG composites prepared at 753 K for 30 mins with an applied pressure of 1.20 GPa exhibited a relative density of 98.3% and a crystallization temperature of 786 K. These nanocrystals were Ta, Cu₅₁Zr₁₄, and other possible Cu–Zr–Ti alloys (e.g., Cu₁₀Zr₇) that were randomly dispersed within the glassy matrix. Full article

The integration of phase-change materials (PCMs) into thermal energy storage systems offers significant potential for reducing energy consumption and improving thermal comfort, crucial issues for achieving sustainable building stocks. Nevertheless, the performance of PCM-based systems is strongly influenced by the container geometry. Among the various forms of incorporating PCMs into building applications, macroencapsulation is the most versatile and is, therefore, widely used. Herewith, this paper analyzes the impact of macrocapsule geometry on PCM thermal performance. Thermal properties of the material were first tested using Differential Scanning Calorimetry at five heating/cooling rates to evaluate its influence on phase-change temperatures and enthalpy. Then, an experimental setup evaluated four macrocapsule geometries on the enclosed PCM behavior during charging and discharging processes. The PCM characterization revealed that the slowest-tested rate minimized the supercooling effect. Analysis across different macrocapsule geometries showed that sectioning the contact surface improved heat transfer efficiency by fully mobilizing the PCM and reducing phase-change times. Conversely, double-layered geometry designs hindered heat transfer, presenting challenges in completing PCM charging and discharging. These findings suggest that optimizing its performance is a necessary direction for further research, which may include adjusting the PCM operating temperature range across layers or redesigning the geometry to misalign contact surfaces. Full article

A novel organic–inorganic eutectic phase change material (PCM) based on sodium acetate trihydrate (SAT) and polyethylene glycol (PEG) was developed to meet the needs of heat recovery and building heating. Three kinds of PEG with different molecular weights were selected to form organic–inorganic eutectic PCM with SAT. The thermal properties of three series of SAT-PEG eutectic PCM were compared based on DSC results, focusing on the impact of PEG addition on the phase change temperature and enthalpy of SAT, as well as the melting uniformity. The inhibitory effects of two nucleating agents on the supercooling of SAT-PEG eutectic PCM were systematically investigated. The effect of PEG on the crystallization behavior of SAT was studied using a metallographic microscope. To evaluate the thermal reliability of the SAT-PEG eutectic PCM, 600 cycles of melting–solidification experiments were conducted. Experimental results show that SAT can form eutectic PCMs with PEG200, PEG600, and PEG6000, respectively, with high enthalpy and excellent melting uniformity. The phase change temperature ranged from 55 °C to 60 °C and the enthalpy was as high as 250–280 kJ/kg. The results of the cooling curves show that 10 wt% tetrasodium pyrophosphate decahydrate (TPD) can reduce the supercooling degree to less than 1 °C. Significantly, all three series of SAT-PEG eutectic PCMs exhibit exceptional thermal reliability after 600 cycles of melting–solidification, with shifts in the phase change temperatures and enthalpies of less than 4%. XRD diffraction patterns showed that SAT, PEG, and TPD were physically mixed without a chemical reaction to form new substances. Microscopic images reveal that the addition of PEG preserves the original needle-shaped crystal morphology of SAT while reducing its crystal size. The rapid formation of small crystals can provide more nucleation points and expedite crystallization, thereby enhancing the heat release capabilities of the PCM. Full article