Journal of Thermal Analysis and Calorimetry最新文献

In this study, banana slices were dried in convective (CD) and modified temperature-controlled microwave drying (MTCM) methods and at 40, 50, 60, and 70 ºC to produce banana chips. The kinetics, energy analysis, and physicochemical properties of the drying processes were investigated. Drying rates varied between 0.0039 and 0.10 g moisture g dry matter minute⁻¹ for drying processes. Effective diffusion values were determined between 8.22 × 10^–8–1.13 × 10^–5 m²s⁻¹ for drying processes. Rehydration capacities were determined between 49.10 and 65.88% for dry methods. Hardness values were determined between 38.00 and 66.30 N for drying processes. Specific moisture absorption rate values were determined to vary between 0.0015 and 0.0099 kgkWh⁻¹. The energy efficiency values were determined to vary between 0.96 and 6.48% for processes, and the latent heat evaporating values ranged between 0.64 and 2.05 kWh. The most suitable (p < 0.05) color values for CD and MTCM were determined at 70 ºC. In this study, the MTCM 70 ºC method is recommended for drying kinetics and physical quality properties. In future studies, a more comprehensive analysis can be conducted by taking into account its bioactive properties.

In practical fluid mechanics, in terms of tube flow description, there is a lack of analytical descriptions and solutions of frictional adiabatic and isentropic flow. This paper explores the connections between the modeling these two flow types and reveals that frictional isentropic flow can be achieved if the heat generated by friction is removed from the flow. This is, in fact, a polytropic flow, which is made isentropic by heat extraction. The study also presents a new description and solution of adiabatic flow, which is not isentropic due to friction, but no heat loss is considered in this work. Adiabatic frictional flow is implemented by extending the application of the adiabatic exponent (k). The adiabatic exponent (k) is naturally used to describe the isentropic or adiabatic state changes of ideal gases. During adiabatic state changes, the entropy of the ideal gas remains unchanged if the state change occurs without internal friction, without internal thermal expansion and without external energy absorption or loss. This means it is no longer an isentropic change of state if there is internal friction in the fluid. The adiabatic change of state without external heat input is therefore not necessarily isentropic. In common terms, a distinction is not always made between adiabatic and isentropic state changes. This paper expands on the use of the adiabatic exponent to describe frictional flows. Further, the paper outlines the possibility of using the exponent k to describe polytropic flows, which, of course, are by no means isentropic, but can be made mathematically so if one can compensate for internal heat generation by external heat extraction.

The use of Calcium silicate hydrate (C–S–H) seeds is a promising solution to accelerate the hydration kinetics of Portland cement mixtures blended containing supplementary cementitious materials (SCM) with a low initial reactivity. However, the interaction mechanisms between C–S–H seeds and alternative SCM, such as Rice husk ash (RHA), are still not fully understood. In this paper, pastes with three levels of Portland cement replacement (10, 20, and 30% by volume of cement) by a high-carbon content RHA were analyzed, with and without the addition of 3% C–S–H seeds. The hydration process and the mechanical performance of the pastes were evaluated through isothermal calorimetry for seven days, thermogravimetric analysis, and compressive strength after 1, 7, and 28 days. The results showed that the C–S–H seeds increased Portlandite consumption during the first hours of the hydration process and enhanced compressive strength after one day of curing. These finds suggested that the use of C–S–H seeds could eliminate the delay in the hydration process and strength development during the initial hours caused by the high-carbon content and low reactivity of RHA.

Coal spontaneous combustion (CSC) is a persistent problem in the field of coal mine safety and is highly detrimental. Clarifying the parallel reactions involved in the process of coal oxidation and spontaneous combustion could provide a new perspective on CSC. The coal–oxygen composite reaction processes of three bituminous coals were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). By establishing a parallel reaction model through multimodal Gaussian fitting, we conclude that the process of coal oxidation and spontaneous combustion involves water evaporation, oxygen adsorption, thermal decomposition, gas phase combustion and solid-phase combustion. These five parallel reactions collectively control the mass and heat changes of coal. The results demonstrate that the ratio of heat intensity to mass is more sensitive to temperature changes in a lower metamorphic coal, which is more likely to undergo gas phase combustion. In the reaction stage dominated by the oxygen adsorption reaction, the apparent activation energies of coal samples, from low to high metamorphic grade, are 60.8, 46.6 and 42.4 kJ mol⁻¹, respectively. Consequently, a higher metamorphic coal is more prone to undergoing the oxygen adsorption reaction.

Graphical abstract

Cotton is one of the most important crops in the world and widely applied in many aspects. However, the fire safety of cotton should be paid attention to for its characteristics of porosity, low ignition point and fast combustion speed. Thermogravimetry-Fourier transform infrared spectroscopy-gas chromatography-mass spectrometry (TG-FTIR-GC/MS) is selected to explore pyrolysis characteristics of cotton. The DTG curves at different heating rates show a single peak with high and narrow shape, indicating that pyrolysis process mainly occurs in a narrow temperature range. The mean value of activation energy is 190.22 kJ mol⁻¹, 190.37 kJ mol⁻¹, 196.96 kJ mol⁻¹ by Kissinger–Akahira–Sunose (KAS), Flynn–Wall–Ozawa (FWO) and Vyazovkin methods, respectively. The F2 reaction model is responsible for the pyrolysis process, and the mechanism function expression is G(α) = − 1[1 − (1 − α)⁻¹] by Coats-Redfern (CR) method. The optimized DTG curve by the shuffled complex evolution (SCE) method is consistent with experimental data. The main intermediate function groups detected by FTIR are C=O at 1750 cm⁻¹ and 2303 cm⁻¹, C–O at 2183 cm⁻¹, O–H at 3574 cm⁻¹, C–H at 2919 cm⁻¹, and the corresponding products are ketones, aldehydes and acids, CO₂, acids, gas H₂O and ketones, aldehydes and hydrocarbon. Seven kinds of gas products including 1H-imidazole-2-methanol, 1-acetoxy-p-menth-3-one, Z-11-pentadecena, 1,6-anhydro-β-D-glucopyranose, Nê-nitro-L-arginine, 7-hexadecyn-1-ol, 3-cyclopentene-1-acetaldehyde were detected in the GC/MS experiment.

For the safe storage of abandoned liquefied fuel tanks, studying the critical temperature threshold for propane tank explosions under transient high-temperature loading is crucial. Transient high temperatures may cause the combustion of residual combustible gases inside abandoned liquefied gas tanks, leading to casualties and property damage. In this paper, numerical simulation methods are employed to investigate the critical temperature exposure time, temperature propagation process and explosion characteristic parameters of propane tanks (propane volume fraction is 4%) under different transient high-temperature loads. The results suggest that propane ignition is influenced by two factors: thermal decomposition and heat conduction. When the high-temperature intensity is fixed, as the exposure time increases, the ignition starting point of propane inside the tank gradually moves toward the upper corners of the tank's sides. At external wall temperatures of 800 K, 1000 K, 1200 K and 1400 K, as the temperature intensity increases, heat propagates more rapidly through the tank's shell. This shortens the explosion delay time and increases the explosion hazard.

A 2D numerical analysis was executed using ANSYS Fluent 16.0 to optimize the dimensions of pentagonal corrugations (corrugation pitch p and angle α) in the absorber plate of a solar air collector of an indirect solar dryer. Initially, α and corrugation height (e) were kept constant and varied the p from 50 to 175 mm, and optimized p was found. Hence, there are 36 sets of results (part-A). This optimized p was used in the second set of simulations where α is varied from 10° to 37.5° with an increment of 2.5°. It has 72 sets of results (part-B). The performance parameters such as Nusselt number (Nu), friction factor (f), Nu ratio, f ratio and thermohydraulic performance parameter (T_hp) were determined for both sets. Nu ratio was from 1.81 to 3.126, which implied that the heat transfer was enriched up to 3.126 times. The maximum T_hp was 1.748 at p = 150 mm. Hence, p = 150 mm is proposed from part-A simulations. In the part-B simulations, the maximum of T_hp was noticed at α = 35° and 37.5°. Considering the material requirement, dimensions of p = 150 mm and α = 37.5° are proposed.

Thermal analysis and calorimetry techniques with sealed sample cells are frequently employed to investigate the thermal stability of hazardous materials. However, the influence of sample mass on thermal decomposition is often ignored. To investigate the effect of sample mass on autocatalytic decomposition substances under sealed condition, 2,4-DNT was chosen for test and analysis. The techniques including differential scanning calorimetry (DSC), rapid screening calorimetry(RSC), high-performance liquid chromatography-mass spectrometry (HPLC–MS), and gas chromatography-mass spectrometry (GC–MS) were utilized for in-depth research on the decomposition of 2,4-DNT. The results revealed that an increase in sample mass led to an significant elevation in gaseous products such as CO₂ and CO with a negative heat of formation (ΔH_f). Then the system pressure and decomposition heat of 2,4-DNT increase significantly, thereby enhancing the thermal decomposition process. After that, it has been determined that o–nitrotoluene, m–nitroaniline, and o–nitrobenzoic acid can catalyze the decomposition of 2,4-DNT. Finally, it is advisable to increase the sample mass as much as possible when testing and analyzing such nitro compounds which would help ensure that the predicted results are closer to the actual conditions of production, transport, storage.

The investigation of velocity slip combined with the dissipative heat corresponds to the non-Newtonian Williamson hybrid nanofluids utilizing the “Cattaneo-Christov heat flux model” is crucial in advanced applications in several sectors. The proposed analysis focuses on the hybrid nanofluid comprised of magnesium oxide (MgO) and zirconium dioxide (ZrO₂) in water which boosts the thermal conductivity along with the performance of the fluid. The magnetized Williamson fluid is a particular type of non-Newtonian fluid that exhibits essential applications to biomedical engineering. The insertion of magnetization along with porosity suggests considering the dissipative heat impact associated with Joule and Darcy which energies the heat transport phenomena. The limitation of classical Fourier laws is addressed by the consideration of the Cattaneo–Christov heat flux framework along with the thermal radiation. The designed flow model with dimensional terms is transformed into a corresponding non-dimensional form by implementing similarity functions. Further, these transmuted equations are solved numerically via the shooting-based Runge–Kutta technique. The parametric analysis of the flow phenomena is obtained and arranged graphically. The validation with earlier investigation displays a valid association in particular scenarios. The main outcomes reveal that the resistivity characteristics produced by the interplay between permeability and magnetization regulate fluid velocity, especially when combined with the non-Newtonian Williamson parameter. Furthermore, in both nanofluid and hybrid nanofluid scenarios, the fluid temperature is greatly raised by the effects of thermal radiation and the Eckert number.