Journal of Thermal Analysis and Calorimetry最新文献

This study deals with the modification of a predominantly amorphous poly(lactic acid) (PLA) by blending it with a semi-crystalline biopolymer, polyhydroxybutyrate-co-valerate (PHBV), which has a high crystallinity. The blends with different concentrations of PLA and PHBV were compounded with spent coffee grounds (SCGs) and processed by injection moulding. The structural, thermal and mechanical properties of the produced samples were investigated. Particular attention was paid to the effect of the presence of SCG and the concentration of PHBV in the blend on the crystallization kinetics and the heat deflection temperature (HDT). For equimolar blends, only a slight increase in HDT (about 5 °C) was observed, but the addition of PHBV suppressed the cold crystallization of PLA, which otherwise negatively affects the dimensional stability of injection moulded parts. A similar effect, but to a lesser extent, was achieved by adding SCG to the PLA matrix. Thus, it is clear that the material structures of PLA/PHBV blends and composites help to minimize additional shrinkage of the parts and increase their dimensional stability. Due to the co-continuous structure of the symmetric PLA/PHBV blends and the increase in the degree of crystallinity from 36 to 47% by annealing the produced samples, the heat deflection temperature increased from 65 up to 90 °C.

This study examines the turbulent heat transfer characteristics of Al₂O₃–Cu hybrid nanofluids in circular ducts with triangular rib configurations. Numerical simulations were conducted for a 25 cm long, -cm high duct with walls maintained at 313 K. Hybrid nanofluids enter at 298 K, with triangular ribs on the internal surface at three attack angles (45°, 60°, and 90°) spaced 20 mm apart. Al2O₃–Cu/H₂O hybrid nanofluids at concentrations of 0.1–2 vol.% were investigated for Reynolds numbers between 20,000 and 60,000. The study aimed to determine the optimal rib configuration and nanofluid concentration for enhancing heat transfer while minimizing friction losses. Key findings include: (1) the 60° rib configuration produced the highest local heat transfer coefficient, with the maximum occurring at the rib centers. (2) Increasing nanofluid concentration and Reynolds number enhanced heat transfer but reduced skin friction. (3) The optimal performance was achieved with 2 vol.% Al₂O₃–Cu at Re = 60,000. (4) Velocity contours revealed larger recirculation zones for 60° ribs compared to 45° and 90° configurations. (5) Turbulent kinetic energy was highest for 60° ribs, contributing to enhanced thermal performance. These findings have implications for improving the efficiency of heat exchangers, cooling systems, and other thermal management applications.

In the present study, numerical investigations are conducted to examine the thermal performance of the magnetohydrodynamic mixed convection flow in a double lid-driven wavy walls square cavity, filled with CNTs. The cavity consists of two undulating lateral walls oriented toward each other, accompanied by horizontal cold walls positioned at the upper and lower ends, exhibiting opposing motion. Governing equations based on the Boussinesq approximation are solved using the CFD analysis. Reynolds numbers, Richardson numbers, Prandtl numbers, Hartmann numbers, nanoparticle volume fractions, wavy walls wave numbers, and amplitudes of waviness affect Nusselt number. The inquiry examines streamlines, isotherms, and Nusselt numbers. Convective current in the hollow enclosure diminishes as Hartmann number increases according to magnetic field strength. Wave number 20 and amplitude 0.1 result in a greater Nu value. Nanoparticles in the primary fluid, at low volume concentrations, quadruple the baseline Nusselt number. SWCNTs (single-walled carbon nanotubes in water) have a high Nusselt number in the heated, wavy-walled enclosure, even under magnetic fields. The investigation reveals a maximum Nusselt number of 91.48 for a volume fraction of 0.1%, three times the previous notable data. This study analyzes how wavy walls, tilted magnetic fields, and CNT-based nanofluids increase enclosures Nusselt number.

Desalination has emerged as a vital solution to tackle global water scarcity, and among various desalination methods, the humidification–dehumidification cycle has garnered significant attention. This study provides a detailed review of performance enhancement techniques utilized in the humidification–dehumidification desalination systems. The review highlights previous studies conducted in this area. The humidification–dehumidification cycle, its working principles, and its advantages and drawbacks are then thoroughly discussed, establishing the groundwork for comprehending the significance of performance improvement strategies. The investigated techniques for multiple facets of the humidification–dehumidification cycle are multistage humidification–dehumidification, bubble columns, phase change materials, nanofluid application, variable pressure humidification–dehumidification, ultrasonic, and other techniques such as thermoelectric application, rotating belt, multiple insert, air saturator, fogging, and desiccant wheel. Through an extensive analysis of existing studies, the review summarizes the key findings of each technique, including improvements in system efficiency, freshwater production rates, heat and mass transfer rates, thermal energy storage, and reduced fouling. The findings provide valuable insights for researchers and practitioners, facilitating the selection and implementation of the most suitable techniques to achieve sustainable and efficient water desalination.

The present work intended to explore the synergistic effects of incorporating carbon nanotubes infused with magnesium oxide nanofluid and dragon fruit extract as a natural additive in photovoltaic–thermal collector systems on its performance in terms of both electrical and thermal energy yield. The proposed methodology was meticulously developed and implemented to assess the efficiency of a hybrid system integrating nano-phase change material and nanofluid in a photovoltaic–thermal configuration. This novel setup was subjected to a comprehensive comparative analysis against a traditional liquid-cooled photovoltaic–thermal system and a standalone photovoltaic module. The study also encompassed variations in cooling techniques, including water with different flow rates for the photovoltaic–thermal system, and the incorporation of nano-phase change material and nanofluid with varying concentrations and flow rates within the hybrid collector. The outcomes demonstrated that at these respective flow rates, the maximum thermal efficiency of the photovoltaic–thermal collector stood at 66.28% and 74.02%. Likewise, the peak electrical efficiency at the same flow rates was recorded as 20.79% and 21.96%. The outcomes of the investigation highlight the higher thermal conductivity of the nanofluid compared to the base fluid, leading to a slight augmentation in fluid density and viscosity. The results obtained from this investigation were found to be consistent with those documented in existing scientific literature.

To investigate the influence of imidazole ionic liquids (IILs) on the whole process of coal spontaneous combustion (CSC). Three IILs, [EMIm][BF₄], [BMIm][BF₄], and [BMIm][NO₃], were selected to carry out thermogravimetry and differential scanning calorimetry (TG–DSC) thermal analysis experiments on long-flame coal. The mass change curve (TG) and enthalpy change curve (DSC) of the coal oxidation process were determined. The characteristic temperatures and stages of the whole process of CSC were also divided by TG and DSC curves, respectively. The influence of IILs on the mass and enthalpy changes were analyzed. Then, the inhibition effect of different IILs on the whole process and each stage of CSC were calculated based on the thermal release, and the inhibition strength of anion and cation was discriminated. From the TG curve, the characteristic temperatures (except T₂) and stages of the treated coal moved toward the high-temperature region of the CSC process compared with the raw coal, the whole mass loss behavior lags behind the raw coal significantly, and the mass loss in the combustion stage is smaller than that of the raw coal. From the DSC curve, the characteristic temperatures (except TD₄) of the treated coal are higher than that of the raw coal, and the thermal release at each stage is lower. Although IILs have a slight facilitating on the accelerated oxidation stage of CSC. However, in general, IILs not only inhibit the occurrence and development of CSC mass loss behavior, but also cause the thermal behavior to end earlier and thermal release reduced. The inhibition effect of the three IILs on spontaneous combustion of long-flame coal is as follows: [EMIm][BF₄] > [BMIm][NO₃] > [BMIm][BF₄], with inhibition effects of 26.5%, 19.4%, and 4.8%, respectively. The inhibition effect on CSC of cation [EMIm]⁺ is better than that of [BMIm]⁺, anion [NO₃]^– is better than that of [BF₄]^–, and the inhibition strength of cation was superior to the anion.

This study introduces an innovative evaluation framework synergizing the analytic hierarchy process (AHP), entropy method, and technique for order preference by similarity to ideal solution (TOPSIS) method to analyze the fire hazards associated with various types of polyurethane foam. By integrating subjective and objective assessments through the AHP-Entropy-TOPSIS method, it transcends the limitations of traditional evaluation techniques, enhancing both accuracy and reliability. Leveraging data from cone calorimeter tests, a detailed hierarchy of fire behavior indicators is established, prioritizing heat release rates and toxic gas emissions as key factors in assessing fire risk. The application of this multi-faceted evaluation framework to five distinct polyurethane materials reveals a clear ranking of fire hazards, highlighting the critical importance of selecting appropriate flame-retardant additives. According to the composite score index evaluated by AHP-Entropy-TOPSIS method, the study concludes that the materials fire hazards are ranked as follows: PU (0.6927) exhibits the highest fire hazard, followed by PU/14APP/1B₄F (0.6044), PU/14APP/1PMA (0.5634), PU/15APP (0.4010), and PU/15BIO (0.3421) presenting the lowest fire hazard among the materials evaluated. This research contributes invaluable insights into fire hazard assessment, guiding material scientists and engineers toward safer polyurethane formulations and advancing the field of fire safety engineering.

Water scarcity is a major issue in cities situated at the Caspian regions of Kazakhstan. To overcome this issue, two compression heat pump-assisted solar thermal desalination configurations are proposed in this research. A numerical model using the TRNSYS simulation package was developed to predict the energy performance of the proposed systems and was validated with experimental results available in the open literature. The influence of ambient parameters and water depth in the basin of a solar still and insulation thickness was analyzed. The performance of proposed configurations is compared with conventional solar still. The errors noticed at 2 and 10 cm depths are 23.6% and 12.1%, respectively. The simulation results confirmed that the heat pump-assisted regenerative solar still configuration has a 91.1%, 73.0%, 61.6% and 82.6% improved productivity during winter, spring, summer and autumn climates, respectively. The results confirmed that significant improvement in freshwater production was observed with heat regeneration compared to the configuration without heat regeneration. The maximum freshwater production with heat regeneration reached 18.0 kg m⁻² day⁻¹ in summer and 9.0 kg m⁻² day⁻¹ in winter. The optimal water depth in the basin is observed to be in the range between 0.5 and 2.0 cm, while the insulation thickness is between 5.0 and 7.0 cm. The results confirmed that the proposed configuration satisfies the water requirements in Kazakhstan.