Journal of Thermal Analysis and Calorimetry最新文献

This study examines the effects of varying permeability and sinusoidal wall temperature fluctuations on the temporal heat transfer flow driven by natural convection inside a rectangular enclosure filled with a glass bead porous medium under local thermal nonequilibrium conditions for both the working fluid and the porous medium. The fluid’s thermal conductivity is assumed to be variable, and a Darcy–Brinkman–Forchheimer model is used to describe the fluid flow. The Galerkin-type finite element method simulates the constitutive equations governing the flow and heat transfer. The simulation explores the influence of different model parameters on the flow and thermal fields. The results indicate that at a steady state ((tau = 1.0)), when glass bead diameter Dp increased from 0.01 to 1.0, the values of (overline{{{text{Nu}}_{{text{f}}} }}) and (overline{{{text{Nu}}_{{text{s}}} }}) decreased by 48.8% and 26%, respectively. Besides, the value of the Nusselt number for the fluid increased by 280.61%, whereas the Nusselt number for the solid increased by 266.55% with the increase of the wave frequency n from 1 to 4. Furthermore, these physical quantities increased by 629.71% and 91.405% when the wave amplitude B rose from 0.1 to 1.

Calcium aluminate phases have a particular effect on the early heat release during setting initiation and have a substantial influence on the further workability of ordinary Portland cement. The nature of the calcium aluminate hydration products and its kinetics strongly depends on sulfate content and humidity. The effect of mineralisers on melt formation and viscosity is well described for calcium silicate systems, but information is still lacking for calcium aluminates. Therefore, the synergistic effect on the crystal structure and hydration mechanism of the tricalcium aluminate phase of the addition of mineralizers, i.e. Li₂O, CuO, SO₃ to the raw meal is here investigated. Co-doped calcium aluminate structures were formed during high-temperature treatment. Thermal analysis (TG–DTA and heating microscopy) was used to describe the ongoing high-temperature reaction. Resulting phase composition was dependent on the concentration of the mineralizer. While phase pure system was prepared with low mineralizer concentrations, with increasing mineralizer content the secondary phases were formed. Raman spectroscopy and XPS analysis were used to investigate the cation substitution and to help describe the cations bonding in co-doped calcium aluminate system. Prepared powders have been hydrated in a controlled manner at different temperatures (288, 298, 308 K). The resulting calorimetric data have been used to investigate the hydration kinetics and determine the rate constant of hydration reaction. First-order reaction (FOR) model was here applied for the activation energy and frequency factor calculations. The metastable and stable calcium aluminate hydrates were formed according to initial phase composition. In phase pure systems with low S content, the formation of stable and metastable hydrates was depended on the reaction temperature. Conversely, in systems with secondary phases and higher S content, the hydration mechanism resembled that which appears in calcium sulfoaluminates.

This paper presents a thermodynamic and sustainability analysis for an experimentally developed solar water heater-with water treatment. The parabolic trough collector (PTC) is employed to capture thermal energy from the sun, which is subsequently utilized to increase the temperature of water. “Experimental and numerical” investigations are divided into two cases. Case 1: PTC with a glass cover and case 2: PTC without glass cover. Using an experimental analysis, data are collected, such as solar insolation and water outlet temperature. The collected data are utilized to analyse the thermodynamic performance of the proposed system. The first law of thermodynamics helps to quantify the system’s performance, called energy analysis, whereas the second law of thermodynamics provides qualitative performance, called exergy analysis. The maximum energy and exergy efficiency achieved by the proposed system are 69.5% and 6.15%, respectively. Simultaneously, an exergy-based sustainability analysis is proposed, which shows how effectively the fuel exergy is utilized with the proposed system. The maximum sustainability index for case 1 is 1.07, and for case 2, it is 1.08. At the end of the experimental investigation, a slight decrease in total dissolved solid (TDS) was detected, indicating that if we enhance the performance of the PTC system, by changing the reflector material and installing evacuated tubes, the quality of the water may improve.

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The relative static permittivity is a pivotal property in electrolyte solutions, playing a crucial role in thermodynamic calculations. This study employs the “Ion − Ion + Ion-Water” approach to calculate individual ionic activity coefficients within various electrolyte solutions at 298.15 K, including aqueous sodium chloride solutions at different temperatures. Two types of relative static permittivity are employed for these calculations: experimental values and modeled values. Notably, the “Ion − Ion + Ion − IWater” approach demonstrates robust performance in determining activity coefficients, regardless of the type of relative static permittivity used. Although minor discrepancies arise between calculations employing these two approaches, this research also delves into the impacts of varying relative static permittivity on activity coefficient determination.

This novel investigation emphasizes the implications of bio-based areca nut husk (ANH)-derived nano-additive on energy, exergy, exergoeconomic, and sustainability aspects of compression ignition engine. X-ray-photoelectron-spectroscopy analysis exhibits the inherent content of oxygen, and nitrogen in ANH at different binding energy levels directing towards its possible use as nanoadditive in diesel at ppm level. From the Brunauer–Emmett–Teller results, it is revealed that ANH nanoparticle is porous in nature having an average pore size of 4.89 nm and a surface area of 3.047 m²g⁻¹. For engine experiments, ANH nano-additives are incorporated at three different proportions at ppm level, and the experiments are carried out at varying loads. The rheological results of nanoadditive mixed diesel exhibit that pumping can be done at a very broad range for diesel with 15 ppm ANH (Diesel-15 ppm) which will endure continuous flow to the engine. The highest energy, exergy efficiency, and sustainability index are observed for Diesel-15 ppm.

Paraffin wax containing n-alkanes has received significant attention in the field of thermal energy storage. The crystallization process is regarded as the main thermal discharging method, which has a profound influence on the thermal performances of paraffin wax. Herein, the phase diagrams of binary systems n-heneicosane + n-pentacosane (C21-C25) and n-pentacosane + n-octacosane (C25-C28) were measured. The results showed that the ordered form was replaced by the rotator form and ultimately transited into a liquid with increasing temperature. Jeziorny and Mo models were used to describe the non-isothermal crystallization process of C25, C21-C25 and C25-28. The effective crystallization activation energy ((Delta {E}_{text{m}})) for the non-isothermal crystallization process of n-alkanes was analyzed using the differential isoconversional method of Friedman. The addition of C21 and C28 was found to have a positive effect on the nucleation; while, a negative effect on the growth process, representing negative net effect on crystallization rate.

The aim of the work is to study the variation in the isobaric heat capacity measurement due to changes in the amount of sample and the calibration standard using a Setaram (mu)DSC3 evo microcalorimeter batch cells to provide a guideline toward the selection of the sample amount to minimize heat capacity measurement error in (mu)DSC. Moreover, overall variation, variation due to the sample amount, and variation due to the calibration standard (reference) amount in heat capacity measurement were estimated for different amounts of the sample or/and the calibration standard material. In the present work, heat capacity measurements were taken for [C₄mim][Tf₂N] (1-butyl-3-methylimidazolium bis[(trifluoromethyl)sulfonyl]imide) ionic liquid as a sample material and 1-butanol as a calibration standard. A novel non-statistical approach, mathematical gnostics (MG), was used for data analysis of measured heat capacities data. Moreover, the artificial neural network (ANN) model was developed to predict the deviation in the heat capacity measurement with 99.83% accuracy and 0.9939 R² score. The Python package PyCpep based on the trained ANN model was developed to predict the deviation in the heat capacity measurement.

The study of fire under high pressure is of great significance for the designing safety protection systems of submarines and underground space stations under high-pressure environment. To investigate the influence of high-pressure on mass burning rate and flame characteristics of square pool fires, three sizes square pools with the length of 2 cm, 4 cm, and 6 cm were carried under high pressure ranged from 1 to 3 atm, and mass burning rate and morphological characteristics of the flame were analyzed. Results showed that the mass burning rates gradually increased as pressure increased, which could be explained by different conduction thermal feedback affected by pressure. The mass burning rates of 4 cm- and 6 cm-length square pool fires were mainly dominated by conduction and convection heat feedback and were proportional to ({P}^{text{n}}), and the exponents were 0.25 and 0.32. But the change of 2 cm-length square pool fire was barely affected by the pressure. As the pressure increasing, the flame oscillation frequency was increased, and the shapes were transformed into relatively unstable because of the enhancement of buoyancy. The color of flame was found to be bright yellow totally owing to the incandescence of soot particles. Moreover, the flame height of 2 cm-length square pool fire increased with pressure increasing and could be expressed as ({h}_{text{f}}/dot{m}propto {P}^{0.23}), while the flame height of other pool fires decreased, which could be demonstrated as ({h}_{text{f}}/{dot{m}}^{2/5}propto {P}^{-0.27}) and ({h}_{text{f}}/{dot{m}}^{2/5}propto {P}^{-0.35}), respectively. Finally, Froude number and Strouhal number were used to characterize the flame pulsation frequency under high pressure. The method presented in this study can provide key scientific data and models to assess fire risk under high pressure.

The present study investigates the influence of iron (Fe) doping on the martensitic transformation and magnetic properties of Ni_50−xMn₃₇Sn₁₃Fe_x(x = 0.5, 1, 1.5) magnetic shape memory alloys in ribbon form. The ribbons were prepared using arc-melting followed by melt-spinning processes and were characterized using X-ray diffraction, scanning electron microscopy, differential scanning calorimetry, and vibrating sample magnetometry. Our findings demonstrate that the addition of Fe shifts the martensitic transformation to lower temperatures and increases the Curie point of the austenitic phase, (T_{c}^{text A}), leading to an enhanced magnetism in the austenitic phase. Moreover, a significant increase in the magnetization jump ((Delta M)) is observed, from ( 3.3;{text{emu g}}^{-1} ) for (x=1) to (17 , {text{emu g}}^{-1} ) for (x=1.5) under a (50 , text {Oe}) applied magnetic field. The structural transformations are also found to be sensitive to the external applied magnetic field. The isothermal magnetization curves exhibit the exchange bias effect, which confirms the coexistence of antiferromagnetic and ferromagnetic coupling in the samples. Furthermore, the exchange bias effect increases with the Fe content.

Lithium-ion batteries are widely used in various industries, particularly in the transportation sectors, owing to their high-power capacity. Despite these advantages, ensuring their safety remains a serious challenge, as thermal runaway and subsequent thermal propagation events pose substantial risks. Various studies have been conducted on the thermal runaway of battery cells. However, research on battery shape and operating conditions is lacking. In this study, the effects of battery shape and operating conditions on the thermal runaway of lithium titanate oxide battery cells are numerically investigated. An equivalent circuit model and NREL’s four-equation model are employed for the electrochemical reactions and thermal runaway. Prismatic cells demonstrated better heat dissipation compared to cylindrical cells, resulting in a delayed onset of thermal runaway but with a higher thermal runaway temperature. Under non-operating conditions, the thermal runaway occurred 40 s later in prismatic cells, with an 83.5 K higher maximum temperature. Conversely, cylindrical cells experienced faster heat accumulation in the core, leading to an earlier onset of thermal runaway by 295 s compared to prismatic cells under operating conditions. Under operating conditions, the onset of thermal runaway was significantly accelerated. Cylindrical cells reached the thermal runaway temperature at 165 s, which is 345 s earlier than under non-operating conditions, with a peak temperature rate of 33.9 K s⁻¹, up from 17.5 K s⁻¹. Similarly, prismatic cells reached a peak temperature rate of 33 K s⁻¹ compared to 18.1 K s⁻¹ under non-operating conditions. These findings underscore the critical role of battery shape and operating conditions in determining the thermal runaway characteristics.